【C言語】atoi/atof/strtol/strtod関数と自作関数で文字列を数値に変換【数値を文字列に変換する自作関数も紹介】

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C言語のatoi/atof/strtol/strtod関数と自作関数で文字列を数値に変換する方法を教えて！

こういった悩みにお答えします．

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C言語で文字列を数値に変換する方法と数値を文字列に変換する方法を紹介します．

本記事を読むと文字列と数値の相互変換をきちんと理解できます．

atoi/atof関数で文字列を数値に変換

atoi/atof関数で文字列を数値に変換する方法を紹介します．

また，これらの関連関数も説明します．

atoi関数で文字列を符号あり整数に変換

int atoi(const char *nptr);
long atol(const char *nptr);
long long atoll(const char *nptr);

int atoi(const char *nptr);

long atol(const char *nptr);

long long atoll(const char *nptr);

atoi/atol/atoll関数で文字列を符号あり整数に変換する方法と，atoi関数の派生関数のatol/atoll関数を紹介します．

atoi/atol/atoll関数の利用例は以下のコードです．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  char s1[] = "123";
  char s2[] = "-4567";

  printf("atoi(%s) = %d\n", s1, atoi(s1));
  printf("atoi(%s) = %d\n", s2, atoi(s2));

  printf("atol(%s) = %ld\n", s1, atol(s1));
  printf("atol(%s) = %ld\n", s2, atol(s2));

  printf("atoll(%s) = %lld\n", s1, atoll(s1));
  printf("atoll(%s) = %lld\n", s2, atoll(s2));

  return 0;
}

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

int main(void)

{

char s1[] = "123";

char s2[] = "-4567";

printf("atoi(%s) = %d\n", s1, atoi(s1));

printf("atoi(%s) = %d\n", s2, atoi(s2));

printf("atol(%s) = %ld\n", s1, atol(s1));

printf("atol(%s) = %ld\n", s2, atol(s2));

printf("atoll(%s) = %lld\n", s1, atoll(s1));

printf("atoll(%s) = %lld\n", s2, atoll(s2));

return 0;

}

実行結果は以下になります．

printf関数のフォーマット指定子の%d，%ld，%lldを利用しているので，符号あり整数として正しく出力されています．

$ gcc atoi.c 
$ a.out 
atoi(123) = 123
atoi(-4567) = -4567
atol(123) = 123
atol(-4567) = -4567
atoll(123) = 123
atoll(-4567) = -4567

$ gcc atoi.c

$ a.out

atoi(123) = 123

atoi(-4567) = -4567

atol(123) = 123

atol(-4567) = -4567

atoll(123) = 123

atoll(-4567) = -4567

atof関数で文字列を浮動小数点数に変換

double atof(const char *nptr);

1	double atof(const char *nptr);

atof関数は，文字列をdouble型の数値に変換します．

atof関数の利用例は以下のコードです．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  char s1[] = "123.45";
  char s2[] = "-4567.89";

  printf("atof(%s) = %lf\n", s1, atof(s1));
  printf("atof(%s) = %lf\n", s2, atof(s2));

  return 0;
}

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

int main(void)

{

char s1[] = "123.45";

char s2[] = "-4567.89";

printf("atof(%s) = %lf\n", s1, atof(s1));

printf("atof(%s) = %lf\n", s2, atof(s2));

return 0;

}

実行結果は以下になります．

printf関数のフォーマット指定子の%lfを利用しているので，浮動小数点数として正しく出力されています．

$ gcc atof.c 
$ a.out 
atof(123.45) = 123.450000
atof(-4567.89) = -4567.890000

$ gcc atof.c

$ a.out

atof(123.45) = 123.450000

atof(-4567.89) = -4567.890000

atoi/atof関数の問題点

atoi/atof関数の問題点として，エラーチェックがないことが挙げられます．

数値以外の不正な文字が文字列に入っているコードは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  char s1[] = "y123z";
  char s2[] = "0";

  printf("atoi(%s) = %d\n", s1, atoi(s1));
  printf("atoi(%s) = %d\n", s2, atoi(s2));

  printf("atol(%s) = %ld\n", s1, atol(s1));
  printf("atol(%s) = %ld\n", s2, atol(s2));

  printf("atoll(%s) = %lld\n", s1, atoll(s1));
  printf("atoll(%s) = %lld\n", s2, atoll(s2));

  return 0;
}

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

int main(void)

{

char s1[] = "y123z";

char s2[] = "0";

printf("atoi(%s) = %d\n", s1, atoi(s1));

printf("atoi(%s) = %d\n", s2, atoi(s2));

printf("atol(%s) = %ld\n", s1, atol(s1));

printf("atol(%s) = %ld\n", s2, atol(s2));

printf("atoll(%s) = %lld\n", s1, atoll(s1));

printf("atoll(%s) = %lld\n", s2, atoll(s2));

return 0;

}

実行結果は以下になります．

文字列"y123z"と"0"を数値に変換した結果が，両方とも0になってしまっています．これだと正しく変換できたかどうかわかりませんね．

$ gcc atoi_error.c
$ a.out
atoi(y123z) = 0
atoi(0) = 0
atol(y123z) = 0
atol(0) = 0
atoll(y123z) = 0
atoll(0) = 0

$ gcc atoi_error.c

$ a.out

atoi(y123z) = 0

atoi(0) = 0

atol(y123z) = 0

atol(0) = 0

atoll(y123z) = 0

atoll(0) = 0

strtol/strtod関数で文字列を数値に変換

エラーチェック付きで文字列を数値に変換するstrtol/strtod関数を紹介します．

また，これらの関連関数も説明します．

strtol関数で文字列を符号あり整数に変換

long strtol(const char *nptr, char **endptr, int base);
long long strtoll(const char *nptr, char **endptr, int base);

1 2	long strtol(const char nptr, char endptr, int base); long long strtoll(const char nptr, char **endptr, int base);

strtol/strtoll関数は，エラーチェック付きで文字列を符号あり整数に変換します．

atoi/atol/atoll関数と同様に，第1引数に変換する文字列nptrを指定します．

第2引数のendptrがNULLでない場合は，最初に現れた不正な文字がstrtol関数により*endptrに保存されます．

文字列に有効な数字がなければ，strtol関数はnptrの元の値を*endptr に代入し0を返します．

特に，*nptr が '\0'以外で返された**endptr が'\0の場合，文字列全体が有効という意味になります．

第3引数のbaseに基数を設定することで，10進数だけでなく2～36進数を変換できます．

もしbaseが0の場合は，変換する先頭の文字列で何進数か判断します．

1文字目が0で2文字目が1から7の場合は8進数，1文字目が0で2文字目がxかXの場合は16進数として変換します．

返り値は，変換された数値になります．

数値がオーバーフローまたはアンダーフローした場合，大域変数errnoにERANGEまたはEINVALが設定されます．

strtol/strtoll関数の利用例は以下のコードです．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

void do_strtol(char *s, int base)
{
  char *endptr;
  long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtol(s, &endptr, base);

  if (errno != 0) {
    perror("strtol()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %ld\n\n", __func__, val);
}

void do_strtoll(char *s, int base)
{
  char *endptr;
  long long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtoll(s, &endptr, base);

  if (errno != 0) {
    perror("strtoll()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %lld\n\n", __func__, val);
}

int main(void)
{
  char s1[] = "123";
  char s2[] = "123z";
  char s3[] = "y123";
  char s4[] = "y123z";
  char s5[] = "yz";
  char s6[] = "99999999999999999999999999999999999999999999999999999999";

  do_strtol(s1, 10);
  do_strtol(s2, 10);
  do_strtol(s3, 10);
  do_strtol(s4, 10);
  do_strtol(s5, 10);
  do_strtol(s6, 10);

  do_strtoll(s1, 10);
  do_strtoll(s2, 10);
  do_strtoll(s3, 10);
  do_strtoll(s4, 10);
  do_strtoll(s5, 10);
  do_strtoll(s6, 10);

  return 0;
}

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <errno.h>

void do_strtol(char *s, int base)

{

char *endptr;

long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtol(s, &endptr, base);

if (errno != 0) {

perror("strtol()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %ld\n\n", __func__, val);

}

void do_strtoll(char *s, int base)

{

char *endptr;

long long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtoll(s, &endptr, base);

if (errno != 0) {

perror("strtoll()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %lld\n\n", __func__, val);

}

int main(void)

{

char s1[] = "123";

char s2[] = "123z";

char s3[] = "y123";

char s4[] = "y123z";

char s5[] = "yz";

char s6[] = "99999999999999999999999999999999999999999999999999999999";

do_strtol(s1, 10);

do_strtol(s2, 10);

do_strtol(s3, 10);

do_strtol(s4, 10);

do_strtol(s5, 10);

do_strtol(s6, 10);

do_strtoll(s1, 10);

do_strtoll(s2, 10);

do_strtoll(s3, 10);

do_strtoll(s4, 10);

do_strtoll(s5, 10);

do_strtoll(s6, 10);

return 0;

}

実行結果は以下になります．

文字列が"123"の場合だけ成功し，符号あり整数123に変換できています（3～4行目，21～22行目）．

他の文字列の場合は，以下の理由でエラーになっています．

数値の後に無効な文字列がある場合（6～7行目，24～25行目）
無効な文字列の場合（9～10行目，12～13行目，15～16行目，27～28行目，30～31行目，33～34行目）
オーバーフローが発生する場合（18～19行目，36～37行目）

$ gcc strtol.c
$ a.out
do_strtol(): s = 123
do_strtol() is successful and val = 123

do_strtol(): s = 123z
Error: invalid digits characters after number: "z"

do_strtol(): s = y123
Error: cannot find valid digits.

do_strtol(): s = y123z
Error: cannot find valid digits.

do_strtol(): s = yz
Error: cannot find valid digits.

do_strtol(): s = 99999999999999999999999999999999999999999999999999999999
strtol(): Numerical result out of range

do_strtoll(): s = 123
do_strtoll() is successful and val = 123

do_strtoll(): s = 123z
Error: invalid digits characters after number: "z"

do_strtoll(): s = y123
Error: cannot find valid digits.

do_strtoll(): s = y123z
Error: cannot find valid digits.

do_strtoll(): s = yz
Error: cannot find valid digits.

do_strtoll(): s = 99999999999999999999999999999999999999999999999999999999
strtoll(): Numerical result out of range

$ gcc strtol.c

$ a.out

do_strtol(): s = 123

do_strtol() is successful and val = 123

do_strtol(): s = 123z

Error: invalid digits characters after number: "z"

do_strtol(): s = y123

Error: cannot find valid digits.

do_strtol(): s = y123z

Error: cannot find valid digits.

do_strtol(): s = yz

Error: cannot find valid digits.

do_strtol(): s = 99999999999999999999999999999999999999999999999999999999

strtol(): Numerical result out of range

do_strtoll(): s = 123

do_strtoll() is successful and val = 123

do_strtoll(): s = 123z

Error: invalid digits characters after number: "z"

do_strtoll(): s = y123

Error: cannot find valid digits.

do_strtoll(): s = y123z

Error: cannot find valid digits.

do_strtoll(): s = yz

Error: cannot find valid digits.

do_strtoll(): s = 99999999999999999999999999999999999999999999999999999999

strtoll(): Numerical result out of range

strtoul関数で文字列を符号なし整数に変換

unsigned long strtoul(const char *nptr, char **endptr, int base);
unsigned long long strtoull(const char *nptr, char **endptr, int base);

1 2	unsigned long strtoul(const char nptr, char endptr, int base); unsigned long long strtoull(const char nptr, char **endptr, int base);

strtoul/strtoull関数は，文字列を符号なし整数に変換します．

strtoul/strtoull関数は，いわゆるstrtol/strtoll関数の符号なしです．

strtoul/strtoull関数の利用例は以下のコードです．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

void do_strtoul(char *s, int base)
{
  char *endptr;
  long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtoul(s, &endptr, base);

  if (errno != 0) {
    perror("strtoul()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %ld\n\n", __func__, val);
}

void do_strtoull(char *s, int base)
{
  char *endptr;
  long long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtoull(s, &endptr, base);

  if (errno != 0) {
    perror("strtoull()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %lld\n\n", __func__, val);
}

int main(void)
{
  char s1[] = "123";
  char s2[] = "123z";
  char s3[] = "y123";
  char s4[] = "y123z";
  char s5[] = "yz";
  char s6[] = "99999999999999999999999999999999999999999999999999999999";

  do_strtoul(s1, 10);
  do_strtoul(s2, 10);
  do_strtoul(s3, 10);
  do_strtoul(s4, 10);
  do_strtoul(s5, 10);
  do_strtoul(s6, 10);

  do_strtoull(s1, 10);
  do_strtoull(s2, 10);
  do_strtoull(s3, 10);
  do_strtoull(s4, 10);
  do_strtoull(s5, 10);
  do_strtoull(s6, 10);

  return 0;
}

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <errno.h>

void do_strtoul(char *s, int base)

{

char *endptr;

long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtoul(s, &endptr, base);

if (errno != 0) {

perror("strtoul()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %ld\n\n", __func__, val);

}

void do_strtoull(char *s, int base)

{

char *endptr;

long long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtoull(s, &endptr, base);

if (errno != 0) {

perror("strtoull()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %lld\n\n", __func__, val);

}

int main(void)

{

char s1[] = "123";

char s2[] = "123z";

char s3[] = "y123";

char s4[] = "y123z";

char s5[] = "yz";

char s6[] = "99999999999999999999999999999999999999999999999999999999";

do_strtoul(s1, 10);

do_strtoul(s2, 10);

do_strtoul(s3, 10);

do_strtoul(s4, 10);

do_strtoul(s5, 10);

do_strtoul(s6, 10);

do_strtoull(s1, 10);

do_strtoull(s2, 10);

do_strtoull(s3, 10);

do_strtoull(s4, 10);

do_strtoull(s5, 10);

do_strtoull(s6, 10);

return 0;

}

実行結果は以下になります．

strtol/strtoll関数と同様です．

$ gcc strtoul.c 
$ a.out 
do_strtoul(): s = 123
do_strtoul() is successful and val = 123

do_strtoul(): s = 123z
Error: invalid digits characters after number: "z"

do_strtoul(): s = y123
Error: cannot find valid digits.

do_strtoul(): s = y123z
Error: cannot find valid digits.

do_strtoul(): s = yz
Error: cannot find valid digits.

do_strtoul(): s = 99999999999999999999999999999999999999999999999999999999
strtoul(): Numerical result out of range

do_strtoull(): s = 123
do_strtoull() is successful and val = 123

do_strtoull(): s = 123z
Error: invalid digits characters after number: "z"

do_strtoull(): s = y123
Error: cannot find valid digits.

do_strtoull(): s = y123z
Error: cannot find valid digits.

do_strtoull(): s = yz
Error: cannot find valid digits.

do_strtoull(): s = 99999999999999999999999999999999999999999999999999999999
strtoull(): Numerical result out of range

$ gcc strtoul.c

$ a.out

do_strtoul(): s = 123

do_strtoul() is successful and val = 123

do_strtoul(): s = 123z

Error: invalid digits characters after number: "z"

do_strtoul(): s = y123

Error: cannot find valid digits.

do_strtoul(): s = y123z

Error: cannot find valid digits.

do_strtoul(): s = yz

Error: cannot find valid digits.

do_strtoul(): s = 99999999999999999999999999999999999999999999999999999999

strtoul(): Numerical result out of range

do_strtoull(): s = 123

do_strtoull() is successful and val = 123

do_strtoull(): s = 123z

Error: invalid digits characters after number: "z"

do_strtoull(): s = y123

Error: cannot find valid digits.

do_strtoull(): s = y123z

Error: cannot find valid digits.

do_strtoull(): s = yz

Error: cannot find valid digits.

do_strtoull(): s = 99999999999999999999999999999999999999999999999999999999

strtoull(): Numerical result out of range

strtod関数で文字列を浮動小数点数に変換

double strtod(const char *nptr, char **endptr);
float strtof(const char *nptr, char **endptr);
long double strtold(const char *nptr, char **endptr);

double strtod(const char *nptr, char **endptr);

float strtof(const char *nptr, char **endptr);

long double strtold(const char *nptr, char **endptr);

strtod/strtof/strtold関数では，文字列を浮動小数点数に変換する関数です．

strtol/strtoll関数とは異なり，第3引数のbaseはありません．

他はほぼ同様です．

strtod/strtof/strtold関数の利用例は以下のコードです．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

void do_strtod(char *s)
{
  char *endptr;
  double val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtod(s, &endptr);

  if (errno != 0) {
    perror("strtod()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %lf\n\n", __func__, val);
}

void do_strtof(char *s)
{
  char *endptr;
  float val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtof(s, &endptr);

  if (errno != 0) {
    perror("strtof()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %f\n\n", __func__, val);
}

void do_strtold(char *s)
{
  char *endptr;
  long double val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtold(s, &endptr);

  if (errno != 0) {
    perror("strtold()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %Lf\n\n", __func__, val);
}

int main(void)
{
  char s1[] = "123.45";
  char s2[] = "123.45z";
  char s3[] = "y123.45";
  char s4[] = "y123.45z";
  char s5[] = "yz";
  char s6[] = "1.189731e+4933";

  do_strtod(s1);
  do_strtod(s2);
  do_strtod(s3);
  do_strtod(s4);
  do_strtod(s5);
  do_strtod(s6);

  do_strtof(s1);
  do_strtof(s2);
  do_strtof(s3);
  do_strtof(s4);
  do_strtof(s5);
  do_strtof(s6);

  do_strtold(s1);
  do_strtold(s2);
  do_strtold(s3);
  do_strtold(s4);
  do_strtold(s5);
  do_strtold(s6);

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <errno.h>

void do_strtod(char *s)

{

char *endptr;

double val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtod(s, &endptr);

if (errno != 0) {

perror("strtod()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %lf\n\n", __func__, val);

}

void do_strtof(char *s)

{

char *endptr;

float val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtof(s, &endptr);

if (errno != 0) {

perror("strtof()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %f\n\n", __func__, val);

}

void do_strtold(char *s)

{

char *endptr;

long double val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtold(s, &endptr);

if (errno != 0) {

perror("strtold()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %Lf\n\n", __func__, val);

}

int main(void)

{

char s1[] = "123.45";

char s2[] = "123.45z";

char s3[] = "y123.45";

char s4[] = "y123.45z";

char s5[] = "yz";

char s6[] = "1.189731e+4933";

do_strtod(s1);

do_strtod(s2);

do_strtod(s3);

do_strtod(s4);

do_strtod(s5);

do_strtod(s6);

do_strtof(s1);

do_strtof(s2);

do_strtof(s3);

do_strtof(s4);

do_strtof(s5);

do_strtof(s6);

do_strtold(s1);

do_strtold(s2);

do_strtold(s3);

do_strtold(s4);

do_strtold(s5);

do_strtold(s6);

return 0;

}

実行結果は以下になります．

strtol/strtoll関数とほぼ同様です．

$ gcc strtod.c
$ a.out
do_strtod(): s = 123.45
do_strtod() is successful and val = 123.450000

do_strtod(): s = 123.45z
Error: invalid digits characters after number: "z"

do_strtod(): s = y123.45
Error: cannot find valid digits.

do_strtod(): s = y123.45z
Error: cannot find valid digits.

do_strtod(): s = yz
Error: cannot find valid digits.

do_strtod(): s = 1.189731e+4933
strtod(): Numerical result out of range

do_strtof(): s = 123.45
do_strtof() is successful and val = 123.449997

do_strtof(): s = 123.45z
Error: invalid digits characters after number: "z"

do_strtof(): s = y123.45
Error: cannot find valid digits.

do_strtof(): s = y123.45z
Error: cannot find valid digits.

do_strtof(): s = yz
Error: cannot find valid digits.

do_strtof(): s = 1.189731e+4933
strtof(): Numerical result out of range

do_strtold(): s = 123.45
do_strtold() is successful and val = 123.450000

do_strtold(): s = 123.45z
Error: invalid digits characters after number: "z"

do_strtold(): s = y123.45
Error: cannot find valid digits.

do_strtold(): s = y123.45z
Error: cannot find valid digits.

do_strtold(): s = yz
Error: cannot find valid digits.

do_strtold(): s = 1.189731e+4933
strtold(): Numerical result out of range

$ gcc strtod.c

$ a.out

do_strtod(): s = 123.45

do_strtod() is successful and val = 123.450000

do_strtod(): s = 123.45z

Error: invalid digits characters after number: "z"

do_strtod(): s = y123.45

Error: cannot find valid digits.

do_strtod(): s = y123.45z

Error: cannot find valid digits.

do_strtod(): s = yz

Error: cannot find valid digits.

do_strtod(): s = 1.189731e+4933

strtod(): Numerical result out of range

do_strtof(): s = 123.45

do_strtof() is successful and val = 123.449997

do_strtof(): s = 123.45z

Error: invalid digits characters after number: "z"

do_strtof(): s = y123.45

Error: cannot find valid digits.

do_strtof(): s = y123.45z

Error: cannot find valid digits.

do_strtof(): s = yz

Error: cannot find valid digits.

do_strtof(): s = 1.189731e+4933

strtof(): Numerical result out of range

do_strtold(): s = 123.45

do_strtold() is successful and val = 123.450000

do_strtold(): s = 123.45z

Error: invalid digits characters after number: "z"

do_strtold(): s = y123.45

Error: cannot find valid digits.

do_strtold(): s = y123.45z

Error: cannot find valid digits.

do_strtold(): s = yz

Error: cannot find valid digits.

do_strtold(): s = 1.189731e+4933

strtold(): Numerical result out of range

自作関数で文字列を数値に変換

自作関数で文字列を数値に変換する方法を紹介します．

myatoi関数で文字列を符号あり整数に変換

myatoi関数で文字列を符号あり整数に変換するコードは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <stdbool.h>

unsigned int myatoui(const char *nptr)
{
  unsigned int result = 0, value;
  char *ep = (char *) nptr + strlen((char *) nptr);

  if (nptr[0] == '+') {
    nptr++;
  }

  while (*nptr && (value = isdigit(*nptr) ? *nptr - '0' : UINT_MAX)) {
    if (value == UINT_MAX) {
      return 0;
    }

    result = result * 10 + value;
    nptr++;
  }

  if (ep != nptr) {
    return UINT_MAX;
  }

  return result;
}

int myatoi(const char *nptr)
{
  if (*nptr == '-') {
    return -myatoui(nptr + 1);
  }

  return myatoui(nptr);
}

unsigned long myatoul(const char *nptr)
{
  unsigned long result = 0, value;
  char *ep = (char *) nptr + strlen((char *) nptr);

  if (nptr[0] == '+') {
    nptr++;
  }

  while (*nptr && (value = isdigit(*nptr) ? *nptr - '0' : ULONG_MAX)) {
    if (value == ULONG_MAX) {
      return 0;
    }

    result = result * 10 + value;
    nptr++;
  }

  if (ep != nptr) {
    return ULONG_MAX;
  }

  return result;
}

long myatol(const char *nptr)
{
  if (*nptr == '-') {
    return -myatoul(nptr + 1);
  }

  return myatoul(nptr);
}

unsigned long long myatoull(const char *nptr)
{
  unsigned long long result = 0, value;
  char *ep = (char *) nptr + strlen((char *) nptr);

  if (nptr[0] == '+') {
    nptr++;
  }

  while (*nptr && (value = isdigit(*nptr) ? *nptr - '0' : ULLONG_MAX)) {
    if (value == ULLONG_MAX) {
      return 0;
    }

    result = result * 10 + value;
    nptr++;
  }

  if (ep != nptr) {
    return ULLONG_MAX;
  }

  return result;
}

long long myatoll(const char *nptr)
{
  if (*nptr == '-') {
    return -myatoull(nptr + 1);
  }

  return myatoull(nptr);
}

int main(void)
{
  char s1[] = "123";
  char s2[] = "-4567";

  printf("myatoi(%s) = %d\n", s1, myatoi(s1));
  printf("myatoi(%s) = %d\n", s2, myatoi(s2));

  printf("myatol(%s) = %ld\n", s1, myatol(s1));
  printf("myatol(%s) = %ld\n", s2, myatol(s2));

  printf("myatoll(%s) = %lld\n", s1, myatoll(s1));
  printf("myatoll(%s) = %lld\n", s2, myatoll(s2));

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <string.h>

#include <ctype.h>

#include <limits.h>

#include <stdbool.h>

unsigned int myatoui(const char *nptr)

{

unsigned int result = 0, value;

char *ep = (char *) nptr + strlen((char *) nptr);

if (nptr[0] == '+') {

nptr++;

}

while (*nptr && (value = isdigit(*nptr) ? *nptr - '0' : UINT_MAX)) {

if (value == UINT_MAX) {

return 0;

}

result = result * 10 + value;

nptr++;

}

if (ep != nptr) {

return UINT_MAX;

}

return result;

}

int myatoi(const char *nptr)

{

if (*nptr == '-') {

return -myatoui(nptr + 1);

}

return myatoui(nptr);

}

unsigned long myatoul(const char *nptr)

{

unsigned long result = 0, value;

char *ep = (char *) nptr + strlen((char *) nptr);

if (nptr[0] == '+') {

nptr++;

}

while (*nptr && (value = isdigit(*nptr) ? *nptr - '0' : ULONG_MAX)) {

if (value == ULONG_MAX) {

return 0;

}

result = result * 10 + value;

nptr++;

}

if (ep != nptr) {

return ULONG_MAX;

}

return result;

}

long myatol(const char *nptr)

{

if (*nptr == '-') {

return -myatoul(nptr + 1);

}

return myatoul(nptr);

}

unsigned long long myatoull(const char *nptr)

{

unsigned long long result = 0, value;

char *ep = (char *) nptr + strlen((char *) nptr);

if (nptr[0] == '+') {

nptr++;

}

while (*nptr && (value = isdigit(*nptr) ? *nptr - '0' : ULLONG_MAX)) {

if (value == ULLONG_MAX) {

return 0;

}

result = result * 10 + value;

nptr++;

}

if (ep != nptr) {

return ULLONG_MAX;

}

return result;

}

long long myatoll(const char *nptr)

{

if (*nptr == '-') {

return -myatoull(nptr + 1);

}

return myatoull(nptr);

}

int main(void)

{

char s1[] = "123";

char s2[] = "-4567";

printf("myatoi(%s) = %d\n", s1, myatoi(s1));

printf("myatoi(%s) = %d\n", s2, myatoi(s2));

printf("myatol(%s) = %ld\n", s1, myatol(s1));

printf("myatol(%s) = %ld\n", s2, myatol(s2));

printf("myatoll(%s) = %lld\n", s1, myatoll(s1));

printf("myatoll(%s) = %lld\n", s2, myatoll(s2));

return 0;

}

実行結果は以下になります．

$ gcc myatoi.c
$ a.out 
myatoi(123) = 123
myatoi(-4567) = -4567
myatol(123) = 123
myatol(-4567) = -4567
myatoll(123) = 123
myatoll(-4567) = -4567

$ gcc myatoi.c

$ a.out

myatoi(123) = 123

myatoi(-4567) = -4567

myatol(123) = 123

myatol(-4567) = -4567

myatoll(123) = 123

myatoll(-4567) = -4567

myatof関数で文字列を浮動小数点数に変換

myatof関数で文字列を浮動小数点数に変換するコードは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdbool.h>
#include <ctype.h>
#include <limits.h>

long lpow(long x, long y)
{
  long ret = 1;
  int i;

  for (i = 0; i < y; i++) {
    ret *= x;
  }

  return ret;
}

double myatof(const char *nptr)
{
  bool valid = false;
  double value = 0.0;
  double sign = 1.0;
  double psign;
  double small;
  double p;

  if (*nptr == '+') {
    nptr++;
  } else if (*nptr == '-') {
    sign = -1.0;
    nptr++;
  }

  if (isdigit((unsigned char) *nptr)) {
    valid = true;

    do {
      value = value * 10.0 + (*nptr - '0');
      nptr++;
    } while (isdigit((unsigned char) *nptr));
  }

  if (*nptr == '.') {
    valid = false;
    nptr++;

    if (isdigit((unsigned char) *nptr)) {
      small = 0.1;
      valid = true;

      do {
        value += small * (*nptr - '0');
        small *= 0.1;
        nptr++;
      } while (isdigit((unsigned char) *nptr));
    }
  }

  if (valid && (*nptr == 'e' || *nptr == 'E')) {
    nptr++;
    valid = false;
    psign = +1.0;

    if (*nptr == '+') {
      nptr++;
    } else if (*nptr == '-') {
      psign = -1.0;
      nptr++;
    }

    if (isdigit((unsigned char) *nptr)) {
      valid = true;
      p = 0.0;

      do {
        p = p * 10.0 + (*nptr - '0');
        nptr++;
      } while (isdigit((unsigned char) *nptr));

      value *= lpow(10.0, psign * p);
    }
  }

  return sign * value;
}

int main(void)
{
  char s1[] = "123.45";
  char s2[] = "-4567.89";

  printf("myatof(%s) = %lf\n", s1, myatof(s1));
  printf("myatof(%s) = %lf\n", s2, myatof(s2));

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdbool.h>

#include <ctype.h>

#include <limits.h>

long lpow(long x, long y)

{

long ret = 1;

int i;

for (i = 0; i < y; i++) {

ret *= x;

}

return ret;

}

double myatof(const char *nptr)

{

bool valid = false;

double value = 0.0;

double sign = 1.0;

double psign;

double small;

double p;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

sign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

do {

value = value * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (*nptr == '.') {

valid = false;

nptr++;

if (isdigit((unsigned char) *nptr)) {

small = 0.1;

valid = true;

do {

value += small * (*nptr - '0');

small *= 0.1;

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (valid && (*nptr == 'e' || *nptr == 'E')) {

nptr++;

valid = false;

psign = +1.0;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

psign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

p = 0.0;

do {

p = p * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

value *= lpow(10.0, psign * p);

}

return sign * value;

}

int main(void)

{

char s1[] = "123.45";

char s2[] = "-4567.89";

printf("myatof(%s) = %lf\n", s1, myatof(s1));

printf("myatof(%s) = %lf\n", s2, myatof(s2));

return 0;

}

実行結果は以下になります．

$ gcc myatof.c
$ a.out 
myatof(123.45) = 123.450000
myatof(-4567.89) = -4567.890000

$ gcc myatof.c

$ a.out

myatof(123.45) = 123.450000

myatof(-4567.89) = -4567.890000

mystrtol関数で文字列を符号あり整数に変換

mystrol/mystrtoll関数で文字列を符号あり整数に変換するコードは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <ctype.h>
#include <limits.h>
#include <errno.h>

long mystrtol(const char *nptr, char **endp, int base)
{
  unsigned long result = 0, value;
  char *ep = (char *) nptr + strlen((char *) nptr);
  int sign = 1;

  if (base != 0 && !(base >= 2 && base <= 36)) {
    errno = EINVAL;
    return 0;
  }

  if (*nptr == '-') {
    sign = -1;
  }

  if (nptr[0] == '+') {
    nptr++;
  }

  if (!base) {
    base = 10;

    if (*nptr == '0') {
      base = 8;
      nptr++;

      if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {
        nptr++;
        base = 16;
      }
    }
  } else if (base == 16) {
    if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {
      nptr += 2;
    }
  }

  while (isxdigit(*nptr)
         && (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)
         < (unsigned long) base) {
    if (sign == 1 && result > (LONG_MAX - value) / base) {
      errno = ERANGE;
      return LONG_MAX;
    } else if (sign == -1
               && result > ((unsigned long) LONG_MAX + 1 - value) / base) {
      errno = ERANGE;
      return LONG_MIN;
    }

    result = result * base + value;
    nptr++;
  }

  if (endp) {
    *endp = (char *) nptr;
  }

  if (ep != nptr) {
    return LONG_MAX;
  }

  return result;
}

void do_mystrtol(char *s, int base)
{
  char *endptr;
  long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = mystrtol(s, &endptr, base);

  if (errno != 0) {
    perror("mystrtol()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %ld\n\n", __func__, val);
}

long long mystrtoll(const char *nptr, char **endp, int base)
{
  unsigned long long result = 0, value;
  char *ep = (char *) nptr + strlen((char *) nptr);
  int sign = 1;

  if (base != 0 && !(base >= 2 && base <= 36)) {
    errno = EINVAL;
    return 0;
  }

  if (*nptr == '-') {
    sign = -1;
  }

  if (nptr[0] == '+') {
    nptr++;
  }

  if (!base) {
    base = 10;

    if (*nptr == '0') {
      base = 8;
      nptr++;

      if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {
        nptr++;
        base = 16;
      }
    }
  } else if (base == 16) {
    if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {
      nptr += 2;
    }
  }

  while (isxdigit(*nptr)
         && (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)
         < (unsigned long long) base) {
    if (sign == 1 && result > (LLONG_MAX - value) / base) {
      errno = ERANGE;
      return LLONG_MAX;
    } else if (sign == -1
               && result > ((unsigned long) LLONG_MAX + 1 - value) / base) {
      errno = ERANGE;
      return LLONG_MIN;
    }

    result = result * base + value;
    nptr++;
  }

  if (endp) {
    *endp = (char *) nptr;
  }

  if (ep != nptr) {
    return LLONG_MAX;
  }

  return result;
}

void do_mystrtoll(char *s, int base)
{
  char *endptr;
  long long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = mystrtoll(s, &endptr, base);

  if (errno != 0) {
    perror("mystrtoll()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %lld\n\n", __func__, val);
}

int main(void)
{
  char s1[] = "123";
  char s2[] = "123z";
  char s3[] = "y123";
  char s4[] = "y123z";
  char s5[] = "yz";
  char s6[] = "99999999999999999999999999999999999999999999999999999999";

  do_mystrtol(s1, 10);
  do_mystrtol(s2, 10);
  do_mystrtol(s3, 10);
  do_mystrtol(s4, 10);
  do_mystrtol(s5, 10);
  do_mystrtol(s6, 10);

  do_mystrtoll(s1, 10);
  do_mystrtoll(s2, 10);
  do_mystrtoll(s3, 10);
  do_mystrtoll(s4, 10);
  do_mystrtoll(s5, 10);
  do_mystrtoll(s6, 10);

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <stdbool.h>

#include <ctype.h>

#include <limits.h>

#include <errno.h>

long mystrtol(const char *nptr, char **endp, int base)

{

unsigned long result = 0, value;

char *ep = (char *) nptr + strlen((char *) nptr);

int sign = 1;

if (base != 0 && !(base >= 2 && base <= 36)) {

errno = EINVAL;

return 0;

}

if (*nptr == '-') {

sign = -1;

}

if (nptr[0] == '+') {

nptr++;

}

if (!base) {

base = 10;

if (*nptr == '0') {

base = 8;

nptr++;

if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {

nptr++;

base = 16;

}

} else if (base == 16) {

if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {

nptr += 2;

}

while (isxdigit(*nptr)

&& (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)

< (unsigned long) base) {

if (sign == 1 && result > (LONG_MAX - value) / base) {

errno = ERANGE;

return LONG_MAX;

} else if (sign == -1

&& result > ((unsigned long) LONG_MAX + 1 - value) / base) {

errno = ERANGE;

return LONG_MIN;

}

result = result * base + value;

nptr++;

}

if (endp) {

*endp = (char *) nptr;

}

if (ep != nptr) {

return LONG_MAX;

}

return result;

}

void do_mystrtol(char *s, int base)

{

char *endptr;

long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = mystrtol(s, &endptr, base);

if (errno != 0) {

perror("mystrtol()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %ld\n\n", __func__, val);

}

long long mystrtoll(const char *nptr, char **endp, int base)

{

unsigned long long result = 0, value;

char *ep = (char *) nptr + strlen((char *) nptr);

int sign = 1;

if (base != 0 && !(base >= 2 && base <= 36)) {

errno = EINVAL;

return 0;

}

if (*nptr == '-') {

sign = -1;

}

if (nptr[0] == '+') {

nptr++;

}

if (!base) {

base = 10;

if (*nptr == '0') {

base = 8;

nptr++;

if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {

nptr++;

base = 16;

}

} else if (base == 16) {

if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {

nptr += 2;

}

while (isxdigit(*nptr)

&& (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)

< (unsigned long long) base) {

if (sign == 1 && result > (LLONG_MAX - value) / base) {

errno = ERANGE;

return LLONG_MAX;

} else if (sign == -1

&& result > ((unsigned long) LLONG_MAX + 1 - value) / base) {

errno = ERANGE;

return LLONG_MIN;

}

result = result * base + value;

nptr++;

}

if (endp) {

*endp = (char *) nptr;

}

if (ep != nptr) {

return LLONG_MAX;

}

return result;

}

void do_mystrtoll(char *s, int base)

{

char *endptr;

long long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = mystrtoll(s, &endptr, base);

if (errno != 0) {

perror("mystrtoll()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %lld\n\n", __func__, val);

}

int main(void)

{

char s1[] = "123";

char s2[] = "123z";

char s3[] = "y123";

char s4[] = "y123z";

char s5[] = "yz";

char s6[] = "99999999999999999999999999999999999999999999999999999999";

do_mystrtol(s1, 10);

do_mystrtol(s2, 10);

do_mystrtol(s3, 10);

do_mystrtol(s4, 10);

do_mystrtol(s5, 10);

do_mystrtol(s6, 10);

do_mystrtoll(s1, 10);

do_mystrtoll(s2, 10);

do_mystrtoll(s3, 10);

do_mystrtoll(s4, 10);

do_mystrtoll(s5, 10);

do_mystrtoll(s6, 10);

return 0;

}

実行結果は以下になります．

$ gcc mystrtol.c 
$ a.out 
do_mystrtol(): s = 123
do_mystrtol() is successful and val = 123

do_mystrtol(): s = 123z
Error: invalid digits characters after number: "z"

do_mystrtol(): s = y123
Error: cannot find valid digits.

do_mystrtol(): s = y123z
Error: cannot find valid digits.

do_mystrtol(): s = yz
Error: cannot find valid digits.

do_mystrtol(): s = 99999999999999999999999999999999999999999999999999999999
mystrtol(): Numerical result out of range

do_mystrtoll(): s = 123
do_mystrtoll() is successful and val = 123

do_mystrtoll(): s = 123z
Error: invalid digits characters after number: "z"

do_mystrtoll(): s = y123
Error: cannot find valid digits.

do_mystrtoll(): s = y123z
Error: cannot find valid digits.

do_mystrtoll(): s = yz
Error: cannot find valid digits.

do_mystrtoll(): s = 99999999999999999999999999999999999999999999999999999999
mystrtoll(): Numerical result out of range

$ gcc mystrtol.c

$ a.out

do_mystrtol(): s = 123

do_mystrtol() is successful and val = 123

do_mystrtol(): s = 123z

Error: invalid digits characters after number: "z"

do_mystrtol(): s = y123

Error: cannot find valid digits.

do_mystrtol(): s = y123z

Error: cannot find valid digits.

do_mystrtol(): s = yz

Error: cannot find valid digits.

do_mystrtol(): s = 99999999999999999999999999999999999999999999999999999999

mystrtol(): Numerical result out of range

do_mystrtoll(): s = 123

do_mystrtoll() is successful and val = 123

do_mystrtoll(): s = 123z

Error: invalid digits characters after number: "z"

do_mystrtoll(): s = y123

Error: cannot find valid digits.

do_mystrtoll(): s = y123z

Error: cannot find valid digits.

do_mystrtoll(): s = yz

Error: cannot find valid digits.

do_mystrtoll(): s = 99999999999999999999999999999999999999999999999999999999

mystrtoll(): Numerical result out of range

mystrtoul関数で文字列を符号なし整数に変換

mystroul/mystrtoull関数で文字列を符号なし整数に変換するコードは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <ctype.h>
#include <limits.h>
#include <errno.h>

unsigned long mystrtoul(const char *nptr, char **endp, int base)
{
  unsigned long result = 0, value;
  char *ep = (char *) nptr + strlen((char *) nptr);
  int sign = 1;

  if (base != 0 && !(base >= 2 && base <= 36)) {
    errno = EINVAL;
    return 0;
  }

  if (*nptr == '-') {
    sign = -1;
  }

  if (nptr[0] == '+') {
    nptr++;
  }

  if (!base) {
    base = 10;

    if (*nptr == '0') {
      base = 8;
      nptr++;

      if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {
        nptr++;
        base = 16;
      }
    }
  } else if (base == 16) {
    if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {
      nptr += 2;
    }
  }

  while (isxdigit(*nptr)
         && (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)
         < (unsigned long) base) {
    if ((sign == 1 && result > (ULONG_MAX - value) / base)
        || (sign == -1
            && result > ((unsigned long) LONG_MAX + 1 - value) / base)) {
      errno = ERANGE;
      return ULONG_MAX;
    }

    result = result * base + value;
    nptr++;
  }

  if (endp) {
    *endp = (char *) nptr;
  }

  if (ep != nptr) {
    return ULONG_MAX;
  }

  return result;
}

void do_mystrtoul(char *s, int base)
{
  char *endptr;
  long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = mystrtoul(s, &endptr, base);

  if (errno != 0) {
    perror("mystrtoul()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %ld\n\n", __func__, val);
}

unsigned long long mystrtoull(const char *nptr, char **endp, int base)
{
  unsigned long long result = 0, value;
  char *ep = (char *) nptr + strlen((char *) nptr);
  int sign = 1;

  if (base != 0 && !(base >= 2 && base <= 36)) {
    errno = EINVAL;
    return 0;
  }

  if (*nptr == '-') {
    sign = -1;
  }

  if (nptr[0] == '+') {
    nptr++;
  }

  if (!base) {
    base = 10;

    if (*nptr == '0') {
      base = 8;
      nptr++;

      if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {
        nptr++;
        base = 16;
      }
    }
  } else if (base == 16) {
    if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {
      nptr += 2;
    }
  }

  while (isxdigit(*nptr)
         && (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)
         < (unsigned long long) base) {
    if ((sign == 1 && result > (ULLONG_MAX - value) / base)
        || (sign == -1
            && result > ((unsigned long long) LLONG_MAX + 1 - value) / base)) {
      errno = ERANGE;
      return ULLONG_MAX;
    }

    result = result * base + value;
    nptr++;
  }

  if (endp) {
    *endp = (char *) nptr;
  }

  if (ep != nptr) {
    return ULLONG_MAX;
  }

  return result;
}

void do_mystrtoull(char *s, int base)
{
  char *endptr;
  long long val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = mystrtoull(s, &endptr, base);

  if (errno != 0) {
    perror("mystrtoull()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %lld\n\n", __func__, val);
}

int main(void)
{
  char s1[] = "123";
  char s2[] = "123z";
  char s3[] = "y123";
  char s4[] = "y123z";
  char s5[] = "yz";
  char s6[] = "99999999999999999999999999999999999999999999999999999999";

  do_mystrtoul(s1, 10);
  do_mystrtoul(s2, 10);
  do_mystrtoul(s3, 10);
  do_mystrtoul(s4, 10);
  do_mystrtoul(s5, 10);
  do_mystrtoul(s6, 10);

  do_mystrtoull(s1, 10);
  do_mystrtoull(s2, 10);
  do_mystrtoull(s3, 10);
  do_mystrtoull(s4, 10);
  do_mystrtoull(s5, 10);
  do_mystrtoull(s6, 10);

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <stdbool.h>

#include <ctype.h>

#include <limits.h>

#include <errno.h>

unsigned long mystrtoul(const char *nptr, char **endp, int base)

{

unsigned long result = 0, value;

char *ep = (char *) nptr + strlen((char *) nptr);

int sign = 1;

if (base != 0 && !(base >= 2 && base <= 36)) {

errno = EINVAL;

return 0;

}

if (*nptr == '-') {

sign = -1;

}

if (nptr[0] == '+') {

nptr++;

}

if (!base) {

base = 10;

if (*nptr == '0') {

base = 8;

nptr++;

if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {

nptr++;

base = 16;

}

} else if (base == 16) {

if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {

nptr += 2;

}

while (isxdigit(*nptr)

&& (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)

< (unsigned long) base) {

if ((sign == 1 && result > (ULONG_MAX - value) / base)

|| (sign == -1

&& result > ((unsigned long) LONG_MAX + 1 - value) / base)) {

errno = ERANGE;

return ULONG_MAX;

}

result = result * base + value;

nptr++;

}

if (endp) {

*endp = (char *) nptr;

}

if (ep != nptr) {

return ULONG_MAX;

}

return result;

}

void do_mystrtoul(char *s, int base)

{

char *endptr;

long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = mystrtoul(s, &endptr, base);

if (errno != 0) {

perror("mystrtoul()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %ld\n\n", __func__, val);

}

unsigned long long mystrtoull(const char *nptr, char **endp, int base)

{

unsigned long long result = 0, value;

char *ep = (char *) nptr + strlen((char *) nptr);

int sign = 1;

if (base != 0 && !(base >= 2 && base <= 36)) {

errno = EINVAL;

return 0;

}

if (*nptr == '-') {

sign = -1;

}

if (nptr[0] == '+') {

nptr++;

}

if (!base) {

base = 10;

if (*nptr == '0') {

base = 8;

nptr++;

if ((toupper(*nptr) == 'X') && isxdigit(nptr[1])) {

nptr++;

base = 16;

}

} else if (base == 16) {

if (nptr[0] == '0' && toupper(nptr[1]) == 'X') {

nptr += 2;

}

while (isxdigit(*nptr)

&& (value = isdigit(*nptr) ? *nptr - '0' : toupper(*nptr) - 'A' + 10)

< (unsigned long long) base) {

if ((sign == 1 && result > (ULLONG_MAX - value) / base)

|| (sign == -1

&& result > ((unsigned long long) LLONG_MAX + 1 - value) / base)) {

errno = ERANGE;

return ULLONG_MAX;

}

result = result * base + value;

nptr++;

}

if (endp) {

*endp = (char *) nptr;

}

if (ep != nptr) {

return ULLONG_MAX;

}

return result;

}

void do_mystrtoull(char *s, int base)

{

char *endptr;

long long val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = mystrtoull(s, &endptr, base);

if (errno != 0) {

perror("mystrtoull()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %lld\n\n", __func__, val);

}

int main(void)

{

char s1[] = "123";

char s2[] = "123z";

char s3[] = "y123";

char s4[] = "y123z";

char s5[] = "yz";

char s6[] = "99999999999999999999999999999999999999999999999999999999";

do_mystrtoul(s1, 10);

do_mystrtoul(s2, 10);

do_mystrtoul(s3, 10);

do_mystrtoul(s4, 10);

do_mystrtoul(s5, 10);

do_mystrtoul(s6, 10);

do_mystrtoull(s1, 10);

do_mystrtoull(s2, 10);

do_mystrtoull(s3, 10);

do_mystrtoull(s4, 10);

do_mystrtoull(s5, 10);

do_mystrtoull(s6, 10);

return 0;

}

実行結果は以下になります．

$ gcc mystrtoul.c 
$ a.out 
do_mystrtoul(): s = 123
do_mystrtoul() is successful and val = 123

do_mystrtoul(): s = 123z
Error: invalid digits characters after number: "z"

do_mystrtoul(): s = y123
Error: cannot find valid digits.

do_mystrtoul(): s = y123z
Error: cannot find valid digits.

do_mystrtoul(): s = yz
Error: cannot find valid digits.

do_mystrtoul(): s = 99999999999999999999999999999999999999999999999999999999
mystrtoul(): Numerical result out of range

do_mystrtoull(): s = 123
do_mystrtoull() is successful and val = 123

do_mystrtoull(): s = 123z
Error: invalid digits characters after number: "z"

do_mystrtoull(): s = y123
Error: cannot find valid digits.

do_mystrtoull(): s = y123z
Error: cannot find valid digits.

do_mystrtoull(): s = yz
Error: cannot find valid digits.

do_mystrtoull(): s = 99999999999999999999999999999999999999999999999999999999
mystrtoull(): Numerical result out of range

$ gcc mystrtoul.c

$ a.out

do_mystrtoul(): s = 123

do_mystrtoul() is successful and val = 123

do_mystrtoul(): s = 123z

Error: invalid digits characters after number: "z"

do_mystrtoul(): s = y123

Error: cannot find valid digits.

do_mystrtoul(): s = y123z

Error: cannot find valid digits.

do_mystrtoul(): s = yz

Error: cannot find valid digits.

do_mystrtoul(): s = 99999999999999999999999999999999999999999999999999999999

mystrtoul(): Numerical result out of range

do_mystrtoull(): s = 123

do_mystrtoull() is successful and val = 123

do_mystrtoull(): s = 123z

Error: invalid digits characters after number: "z"

do_mystrtoull(): s = y123

Error: cannot find valid digits.

do_mystrtoull(): s = y123z

Error: cannot find valid digits.

do_mystrtoull(): s = yz

Error: cannot find valid digits.

do_mystrtoull(): s = 99999999999999999999999999999999999999999999999999999999

mystrtoull(): Numerical result out of range

mystrtod関数で文字列を浮動小数点数に変換

mystrtod/mystrtof/mystrtold関数で文字列を浮動小数点数に変換するコードは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <ctype.h>
#include <errno.h>

long lpow(long x, long y)
{
  long ret = 1;
  int i;

  for (i = 0; i < y; i++) {
    ret *= x;
  }

  return ret;
}

double mystrtod(const char *nptr, char **endptr)
{
  const char *org = nptr;
  bool valid = false;
  double value = 0.0;
  double sign = 1.0;
  double psign;
  double small;
  double p;

  if (*nptr == '+') {
    nptr++;
  } else if (*nptr == '-') {
    sign = -1.0;
    nptr++;
  }

  if (isdigit((unsigned char) *nptr)) {
    valid = true;

    do {
      value = value * 10.0 + (*nptr - '0');
      nptr++;
    } while (isdigit((unsigned char) *nptr));
  }

  if (*nptr == '.') {
    valid = false;
    nptr++;

    if (isdigit((unsigned char) *nptr)) {
      small = 0.1;
      valid = true;

      do {
        value += small * (*nptr - '0');
        small *= 0.1;
        nptr++;
      } while (isdigit((unsigned char) *nptr));
    }
  }

  if (valid && (*nptr == 'e' || *nptr == 'E')) {
    nptr++;
    valid = false;
    psign = +1.0;

    if (*nptr == '+') {
      nptr++;
    } else if (*nptr == '-') {
      psign = -1.0;
      nptr++;
    }

    if (isdigit((unsigned char) *nptr)) {
      valid = true;
      p = 0.0;

      do {
        p = p * 10.0 + (*nptr - '0');
        nptr++;
      } while (isdigit((unsigned char) *nptr));

      value *= lpow(10.0, psign * p);
    }
  }

  if (valid) {
    *endptr = (char *) nptr;
  } else {
    *endptr = (char *) org;
  }

  return sign * value;
}

void do_strtod(char *s)
{
  char *endptr;
  double val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = mystrtod(s, &endptr);

  if (errno != 0) {
    perror("strtod()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %lf\n\n", __func__, val);
}

float mystrtof(const char *nptr, char **endptr)
{
  const char *org = nptr;
  bool valid = false;
  float value = 0.0;
  float sign = 1.0;
  float psign;
  float small;
  float p;

  if (*nptr == '+') {
    nptr++;
  } else if (*nptr == '-') {
    sign = -1.0;
    nptr++;
  }

  if (isdigit((unsigned char) *nptr)) {
    valid = true;

    do {
      value = value * 10.0 + (*nptr - '0');
      nptr++;
    } while (isdigit((unsigned char) *nptr));
  }

  if (*nptr == '.') {
    valid = false;
    nptr++;

    if (isdigit((unsigned char) *nptr)) {
      small = 0.1;
      valid = true;

      do {
        value += small * (*nptr - '0');
        small *= 0.1;
        nptr++;
      } while (isdigit((unsigned char) *nptr));
    }
  }

  if (valid && (*nptr == 'e' || *nptr == 'E')) {
    nptr++;
    valid = false;
    psign = +1.0;

    if (*nptr == '+') {
      nptr++;
    } else if (*nptr == '-') {
      psign = -1.0;
      nptr++;
    }

    if (isdigit((unsigned char) *nptr)) {
      valid = true;
      p = 0.0;

      do {
        p = p * 10.0 + (*nptr - '0');
        nptr++;
      } while (isdigit((unsigned char) *nptr));

      value *= lpow(10.0, psign * p);
    }
  }

  if (valid) {
    *endptr = (char *) nptr;
  } else {
    *endptr = (char *) org;
  }

  return sign * value;
}

void do_strtof(char *s)
{
  char *endptr;
  float val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtof(s, &endptr);

  if (errno != 0) {
    perror("strtof()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %f\n\n", __func__, val);
}

long double mystrtold(const char *nptr, char **endptr)
{
  const char *org = nptr;
  bool valid = false;
  long double value = 0.0;
  long double sign = 1.0;
  long double psign;
  long double small;
  long double p;

  if (*nptr == '+') {
    nptr++;
  } else if (*nptr == '-') {
    sign = -1.0;
    nptr++;
  }

  if (isdigit((unsigned char) *nptr)) {
    valid = true;

    do {
      value = value * 10.0 + (*nptr - '0');
      nptr++;
    } while (isdigit((unsigned char) *nptr));
  }

  if (*nptr == '.') {
    valid = false;
    nptr++;

    if (isdigit((unsigned char) *nptr)) {
      small = 0.1;
      valid = true;

      do {
        value += small * (*nptr - '0');
        small *= 0.1;
        nptr++;
      } while (isdigit((unsigned char) *nptr));
    }
  }

  if (valid && (*nptr == 'e' || *nptr == 'E')) {
    nptr++;
    valid = false;
    psign = +1.0;

    if (*nptr == '+') {
      nptr++;
    } else if (*nptr == '-') {
      psign = -1.0;
      nptr++;
    }

    if (isdigit((unsigned char) *nptr)) {
      valid = true;
      p = 0.0;

      do {
        p = p * 10.0 + (*nptr - '0');
        nptr++;
      } while (isdigit((unsigned char) *nptr));

      value *= lpow(10.0, psign * p);
    }
  }

  if (valid) {
    *endptr = (char *) nptr;
  } else {
    *endptr = (char *) org;
  }

  return sign * value;
}

void do_strtold(char *s)
{
  char *endptr;
  long double val;

  errno = 0;

  printf("%s(): s = %s\n", __func__, s);
  val = strtold(s, &endptr);

  if (errno != 0) {
    perror("strtold()");
    printf("\n");
    return;
  }

  if (endptr == s) {
    fprintf(stderr, "Error: cannot find valid digits.\n\n");
    return;
  }

  if (*endptr != '\0') {
    fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",
            endptr);
    return;
  }

  printf("%s() is successful and val = %Lf\n\n", __func__, val);
}

int main(void)
{
  char s1[] = "123.45";
  char s2[] = "123.45z";
  char s3[] = "y123.45";
  char s4[] = "y123.45z";
  char s5[] = "yz";
  char s6[] = "1.189731e+4933";

  do_strtod(s1);
  do_strtod(s2);
  do_strtod(s3);
  do_strtod(s4);
  do_strtod(s5);
  do_strtod(s6);

  do_strtof(s1);
  do_strtof(s2);
  do_strtof(s3);
  do_strtof(s4);
  do_strtof(s5);
  do_strtof(s6);

  do_strtold(s1);
  do_strtold(s2);
  do_strtold(s3);
  do_strtold(s4);
  do_strtold(s5);
  do_strtold(s6);

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdlib.h>

#include <stdbool.h>

#include <ctype.h>

#include <errno.h>

long lpow(long x, long y)

{

long ret = 1;

int i;

for (i = 0; i < y; i++) {

ret *= x;

}

return ret;

}

double mystrtod(const char *nptr, char **endptr)

{

const char *org = nptr;

bool valid = false;

double value = 0.0;

double sign = 1.0;

double psign;

double small;

double p;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

sign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

do {

value = value * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (*nptr == '.') {

valid = false;

nptr++;

if (isdigit((unsigned char) *nptr)) {

small = 0.1;

valid = true;

do {

value += small * (*nptr - '0');

small *= 0.1;

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (valid && (*nptr == 'e' || *nptr == 'E')) {

nptr++;

valid = false;

psign = +1.0;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

psign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

p = 0.0;

do {

p = p * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

value *= lpow(10.0, psign * p);

}

if (valid) {

*endptr = (char *) nptr;

} else {

*endptr = (char *) org;

}

return sign * value;

}

void do_strtod(char *s)

{

char *endptr;

double val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = mystrtod(s, &endptr);

if (errno != 0) {

perror("strtod()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %lf\n\n", __func__, val);

}

float mystrtof(const char *nptr, char **endptr)

{

const char *org = nptr;

bool valid = false;

float value = 0.0;

float sign = 1.0;

float psign;

float small;

float p;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

sign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

do {

value = value * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (*nptr == '.') {

valid = false;

nptr++;

if (isdigit((unsigned char) *nptr)) {

small = 0.1;

valid = true;

do {

value += small * (*nptr - '0');

small *= 0.1;

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (valid && (*nptr == 'e' || *nptr == 'E')) {

nptr++;

valid = false;

psign = +1.0;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

psign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

p = 0.0;

do {

p = p * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

value *= lpow(10.0, psign * p);

}

if (valid) {

*endptr = (char *) nptr;

} else {

*endptr = (char *) org;

}

return sign * value;

}

void do_strtof(char *s)

{

char *endptr;

float val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtof(s, &endptr);

if (errno != 0) {

perror("strtof()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %f\n\n", __func__, val);

}

long double mystrtold(const char *nptr, char **endptr)

{

const char *org = nptr;

bool valid = false;

long double value = 0.0;

long double sign = 1.0;

long double psign;

long double small;

long double p;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

sign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

do {

value = value * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (*nptr == '.') {

valid = false;

nptr++;

if (isdigit((unsigned char) *nptr)) {

small = 0.1;

valid = true;

do {

value += small * (*nptr - '0');

small *= 0.1;

nptr++;

} while (isdigit((unsigned char) *nptr));

}

if (valid && (*nptr == 'e' || *nptr == 'E')) {

nptr++;

valid = false;

psign = +1.0;

if (*nptr == '+') {

nptr++;

} else if (*nptr == '-') {

psign = -1.0;

nptr++;

}

if (isdigit((unsigned char) *nptr)) {

valid = true;

p = 0.0;

do {

p = p * 10.0 + (*nptr - '0');

nptr++;

} while (isdigit((unsigned char) *nptr));

value *= lpow(10.0, psign * p);

}

if (valid) {

*endptr = (char *) nptr;

} else {

*endptr = (char *) org;

}

return sign * value;

}

void do_strtold(char *s)

{

char *endptr;

long double val;

errno = 0;

printf("%s(): s = %s\n", __func__, s);

val = strtold(s, &endptr);

if (errno != 0) {

perror("strtold()");

printf("\n");

return;

}

if (endptr == s) {

fprintf(stderr, "Error: cannot find valid digits.\n\n");

return;

}

if (*endptr != '\0') {

fprintf(stderr, "Error: invalid digits characters after number: \"%s\"\n\n",

endptr);

return;

}

printf("%s() is successful and val = %Lf\n\n", __func__, val);

}

int main(void)

{

char s1[] = "123.45";

char s2[] = "123.45z";

char s3[] = "y123.45";

char s4[] = "y123.45z";

char s5[] = "yz";

char s6[] = "1.189731e+4933";

do_strtod(s1);

do_strtod(s2);

do_strtod(s3);

do_strtod(s4);

do_strtod(s5);

do_strtod(s6);

do_strtof(s1);

do_strtof(s2);

do_strtof(s3);

do_strtof(s4);

do_strtof(s5);

do_strtof(s6);

do_strtold(s1);

do_strtold(s2);

do_strtold(s3);

do_strtold(s4);

do_strtold(s5);

do_strtold(s6);

return 0;

}

実行結果は以下になります．

$ gcc mystrtod.c
$ a.out
do_strtod(): s = 123.45
do_strtod() is successful and val = 123.450000

do_strtod(): s = 123.45z
Error: invalid digits characters after number: "z"

do_strtod(): s = y123.45
Error: cannot find valid digits.

do_strtod(): s = y123.45z
Error: cannot find valid digits.

do_strtod(): s = yz
Error: cannot find valid digits.

do_strtod(): s = 1.189731e+4933
strtod(): Numerical result out of range

do_strtof(): s = 123.45
do_strtof() is successful and val = 123.449997

do_strtof(): s = 123.45z
Error: invalid digits characters after number: "z"

do_strtof(): s = y123.45
Error: cannot find valid digits.

do_strtof(): s = y123.45z
Error: cannot find valid digits.

do_strtof(): s = yz
Error: cannot find valid digits.

do_strtof(): s = 1.189731e+4933
strtof(): Numerical result out of range

do_strtold(): s = 123.45
do_strtold() is successful and val = 123.450000

do_strtold(): s = 123.45z
Error: invalid digits characters after number: "z"

do_strtold(): s = y123.45
Error: cannot find valid digits.

do_strtold(): s = y123.45z
Error: cannot find valid digits.

do_strtold(): s = yz
Error: cannot find valid digits.

do_strtold(): s = 1.189731e+4933
strtold(): Numerical result out of range

$ gcc mystrtod.c

$ a.out

do_strtod(): s = 123.45

do_strtod() is successful and val = 123.450000

do_strtod(): s = 123.45z

Error: invalid digits characters after number: "z"

do_strtod(): s = y123.45

Error: cannot find valid digits.

do_strtod(): s = y123.45z

Error: cannot find valid digits.

do_strtod(): s = yz

Error: cannot find valid digits.

do_strtod(): s = 1.189731e+4933

strtod(): Numerical result out of range

do_strtof(): s = 123.45

do_strtof() is successful and val = 123.449997

do_strtof(): s = 123.45z

Error: invalid digits characters after number: "z"

do_strtof(): s = y123.45

Error: cannot find valid digits.

do_strtof(): s = y123.45z

Error: cannot find valid digits.

do_strtof(): s = yz

Error: cannot find valid digits.

do_strtof(): s = 1.189731e+4933

strtof(): Numerical result out of range

do_strtold(): s = 123.45

do_strtold() is successful and val = 123.450000

do_strtold(): s = 123.45z

Error: invalid digits characters after number: "z"

do_strtold(): s = y123.45

Error: cannot find valid digits.

do_strtold(): s = y123.45z

Error: cannot find valid digits.

do_strtold(): s = yz

Error: cannot find valid digits.

do_strtold(): s = 1.189731e+4933

strtold(): Numerical result out of range

自作関数で数値を文字列に変換

数値を文字列に変換する標準ライブラリ関数はありません．

なので，自作関数で数値を文字列に変換する方法を紹介します．

myitoa関数で整数を文字列に変換

myitoa関数で整数を文字列に変換するコードは以下になります．

符号ありと符号なしの両方やに対応しています．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>
#include <stdbool.h>
#include <ctype.h>

#define BUFSIZE 64

void myxtoa(unsigned long long val, char *str, int base, bool negative)
{
  char *p;
  char *firstdig;
  char temp;
  unsigned long long digval;

  if (base != 0 && !(base >= 2 && base <= 36)) {
    fprintf(stderr, "Error: invalid base %u\n", base);
    return;
  }

  p = str;

  if (negative) {
    *p++ = '-';
    val = (unsigned long long)(-(long long) val);
  }

  if (!base) {
    base = 10;

    if (*str == '0') {
      base = 8;
      str++;

      if ((toupper(*str) == 'X') && isxdigit(str[1])) {
        str++;
        base = 16;
      }
    }
  } else if (base == 16) {
    if (str[0] == '0' && toupper(str[1]) == 'X') {
      str += 2;
    }
  }

  firstdig = p;

  do {
    digval = (unsigned long long)(val % base);
    val /= base;

    if (digval > 9) {
      *p++ = (char)(digval - 10 + 'a');
    } else {
      *p++ = (char)(digval + '0');
    }
  } while (val > 0);

  *p-- = '\0';

  do {
    temp = *p;
    *p = *firstdig;
    *firstdig = temp;
    p--;
    firstdig++;
  } while (firstdig < p);
}

char *myitoa(int val, char *str, int base)
{
  if (base == 10 && val < 0) {
    myxtoa(val, str, base, true);
  } else {
    myxtoa(val, str, base, false);
  }

  return str;
}

char *myltoa(long val, char *str, int base)
{
  myxtoa(val, str, base, (base == 10 && val < 0));
  return str;
}

char *mylltoa(long long val, char *str, int base)
{
  myxtoa(val, str, base, (base == 10 && val < 0));
  return str;
}

int main(void)
{
  int i1 = 123;
  int i2 = -456;
  long l1 = 1234;
  long l2 = -5678;
  long long ll1 = 12345;
  long long ll2 = -67890;
  char s[BUFSIZE];

  myitoa(i1, s, 10);
  printf("i1 = %d, s = %s\n", i1, s);

  myitoa(i2, s, 10);
  printf("i2 = %d, s = %s\n", i2, s);

  myltoa(l1, s, 10);
  printf("l1 = %ld, s = %s\n", l1, s);

  myltoa(l2, s, 10);
  printf("l2 = %ld, s = %s\n", l2, s);

  mylltoa(l1, s, 10);
  printf("ll1 = %lld, s = %s\n", ll1, s);

  mylltoa(l2, s, 10);
  printf("ll2 = %lld, s = %s\n", ll2, s);

  return 0;
}

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* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#include <stdbool.h>

#include <ctype.h>

#define BUFSIZE 64

void myxtoa(unsigned long long val, char *str, int base, bool negative)

{

char *p;

char *firstdig;

char temp;

unsigned long long digval;

if (base != 0 && !(base >= 2 && base <= 36)) {

fprintf(stderr, "Error: invalid base %u\n", base);

return;

}

p = str;

if (negative) {

*p++ = '-';

val = (unsigned long long)(-(long long) val);

}

if (!base) {

base = 10;

if (*str == '0') {

base = 8;

str++;

if ((toupper(*str) == 'X') && isxdigit(str[1])) {

str++;

base = 16;

}

} else if (base == 16) {

if (str[0] == '0' && toupper(str[1]) == 'X') {

str += 2;

}

firstdig = p;

do {

digval = (unsigned long long)(val % base);

val /= base;

if (digval > 9) {

*p++ = (char)(digval - 10 + 'a');

} else {

*p++ = (char)(digval + '0');

}

} while (val > 0);

*p-- = '\0';

do {

temp = *p;

*p = *firstdig;

*firstdig = temp;

p--;

firstdig++;

} while (firstdig < p);

}

char *myitoa(int val, char *str, int base)

{

if (base == 10 && val < 0) {

myxtoa(val, str, base, true);

} else {

myxtoa(val, str, base, false);

}

return str;

}

char *myltoa(long val, char *str, int base)

{

myxtoa(val, str, base, (base == 10 && val < 0));

return str;

}

char *mylltoa(long long val, char *str, int base)

{

myxtoa(val, str, base, (base == 10 && val < 0));

return str;

}

int main(void)

{

int i1 = 123;

int i2 = -456;

long l1 = 1234;

long l2 = -5678;

long long ll1 = 12345;

long long ll2 = -67890;

char s[BUFSIZE];

myitoa(i1, s, 10);

printf("i1 = %d, s = %s\n", i1, s);

myitoa(i2, s, 10);

printf("i2 = %d, s = %s\n", i2, s);

myltoa(l1, s, 10);

printf("l1 = %ld, s = %s\n", l1, s);

myltoa(l2, s, 10);

printf("l2 = %ld, s = %s\n", l2, s);

mylltoa(l1, s, 10);

printf("ll1 = %lld, s = %s\n", ll1, s);

mylltoa(l2, s, 10);

printf("ll2 = %lld, s = %s\n", ll2, s);

return 0;

}

実行結果は以下になります．

$ gcc myitoa.c
$ a.out
i1 = 123, s = 123
i2 = -456, s = -456
l1 = 1234, s = 1234
l2 = -5678, s = -5678
ll1 = 12345, s = 1234
ll2 = -67890, s = -5678

$ gcc myitoa.c

$ a.out

i1 = 123, s = 123

i2 = -456, s = -456

l1 = 1234, s = 1234

l2 = -5678, s = -5678

ll1 = 12345, s = 1234

ll2 = -67890, s = -5678

myftoa関数で浮動小数点数を文字列に変換

myftoa関数で浮動小数点数を文字列に変換するコードは以下になります．

/*
 * Author: Hiroyuki Chishiro
 * License: 2-Clause BSD
 */
#include <stdio.h>

#define BUFSIZE 64

long lpow(long x, long y)
{
  long ret = 1;
  int i;

  for (i = 0; i < y; i++) {
    ret *= x;
  }

  return ret;
}

char *myftoa(double d, char *buf, int precision)
{
  char *ptr = buf;
  char *p = ptr;
  char *p1;
  char c;
  long int_part;
  double rounders;

  if (d < 0) {
    d = -d;
    *ptr++ = '-';
  }

  if (precision < 0) {
    precision = 1;
  }

  rounders = 0.5 / lpow(10.0, precision);

  if (precision) {
    d += rounders;
  }

  int_part = d;
  d -= int_part;

  if (!int_part) {
    *ptr++ = '0';
  } else {
    p = ptr;

    while (int_part) {
      *p++ = '0' + int_part % 10;
      int_part /= 10;
    }

    p1 = p;

    while (p > ptr) {
      c = *--p;
      *p = *ptr;
      *ptr++ = c;
    }

    ptr = p1;
  }

  if (precision) {
    *ptr++ = '.';

    while (precision--) {
      d *= 10.0;
      c = d;
      *ptr++ = '0' + c;
      d -= c;
    }
  }

  *ptr = '\0';

  return buf;
}

int main(void)
{
  double d1 = 123.45;
  double d2 = -4557.89;
  char s[BUFSIZE];

  myftoa(d1, s, 6);
  printf("d1 = %lf, s = %s\n", d1, s);

  myftoa(d2, s, 6);
  printf("d2 = %lf, s = %s\n", d2, s);

  return 0;
}

* Author: Hiroyuki Chishiro

* License: 2-Clause BSD

#include <stdio.h>

#define BUFSIZE 64

long lpow(long x, long y)

{

long ret = 1;

int i;

for (i = 0; i < y; i++) {

ret *= x;

}

return ret;

}

char *myftoa(double d, char *buf, int precision)

{

char *ptr = buf;

char *p = ptr;

char *p1;

char c;

long int_part;

double rounders;

if (d < 0) {

d = -d;

*ptr++ = '-';

}

if (precision < 0) {

precision = 1;

}

rounders = 0.5 / lpow(10.0, precision);

if (precision) {

d += rounders;

}

int_part = d;

d -= int_part;

if (!int_part) {

*ptr++ = '0';

} else {

p = ptr;

while (int_part) {

*p++ = '0' + int_part % 10;

int_part /= 10;

}

p1 = p;

while (p > ptr) {

c = *--p;

*p = *ptr;

*ptr++ = c;

}

ptr = p1;

}

if (precision) {

*ptr++ = '.';

while (precision--) {

d *= 10.0;

c = d;

*ptr++ = '0' + c;

d -= c;

}

*ptr = '\0';

return buf;

}

int main(void)

{

double d1 = 123.45;

double d2 = -4557.89;

char s[BUFSIZE];

myftoa(d1, s, 6);

printf("d1 = %lf, s = %s\n", d1, s);

myftoa(d2, s, 6);

printf("d2 = %lf, s = %s\n", d2, s);

return 0;

}

実行結果は以下になります．

$ gcc myftoa.c
$ a.out 
d1 = 123.450000, s = 123.450000
d2 = -4557.890000, s = -4557.890000

$ gcc myftoa.c

$ a.out

d1 = 123.450000, s = 123.450000

d2 = -4557.890000, s = -4557.890000

まとめ

C言語のatoi/atof関数で文字列を数値に変換する方法を紹介しました．

また，これらの関数はエラーチェックがないため，エラーチェックがあるstrtol/strtod関数，逆に数値を文字列に変換する自作関数も紹介しました．

C言語で文字列と数値の相互変換をしたいあなたにおすすめのコードですので，是非利用しましょう！

C言語を独学で習得することは難しいです．

私にC言語の無料相談をしたいあなたは，公式LINE「ChishiroのC言語」の友だち追加をお願い致します．

私のキャパシティもあり，一定数に達したら終了しますので，今すぐ追加しましょう！

: 元東大教員がおすすめするC言語を学べるオンラインプログラミングスクール5社

こういった悩みにお答えします．こういった私が解説していきます．私が大学の授業で初めてC言語を勉強した時は全然できませんでしたが，先生やTA，友人に相談しながら一生懸命C言語を勉強してできるようにな ...

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