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  1. #include <errno.h>  /* errno, EINVAL, ERANGE */
  2. #include <limits.h> /* INT_MIN, INT_MAX */
  3. #include <stdio.h>  /* printf(), fprintf(), stderr */
  4. #include <stdlib.h> /* strtol() */
  5. #include <string.h> /* strerror() */
  6.  
  7. /* Convert a string to an int. */
  8. int
  9. str_to_int_strtol(const char *s)
  10. {
  11. 	char *s_rem;
  12. 	long l;
  13. 	int errno_save = errno;
  14.  
  15. 	errno = 0;
  16. 	l = strtol(s, &s_rem, 10);
  17. 	if (errno == 0) {
  18. 		/* Number out of range. */
  19. 		if (l < INT_MIN || l > INT_MAX)
  20. 			errno = ERANGE;
  21.  
  22. 		/* Argument isn't completely made up of decimal digits. */
  23. 		else if (*s_rem != '\0')
  24. 			errno = EINVAL;
  25. 	}
  26. 	if (errno) {
  27. 		fprintf(stderr, "strtol() error: operand \"%s\": %s\n", s,
  28. 		    strerror(errno));
  29. 		return 0;
  30. 	}
  31.  
  32. 	errno = errno_save;
  33. 	return (int)l;
  34. }
  35.  
  36. /* Convert a string to an int (less robust). */
  37. int
  38. str_to_int_atoi(const char *s)
  39. {
  40. 	int n;
  41. 	int errno_save = errno;
  42.  
  43. 	errno = 0;
  44. 	n = atoi(s);
  45.  
  46. 	if (errno != 0) {
  47. 		fprintf(stderr, "atoi() error: operand \"%s\": %s\n", s,
  48. 		    strerror(errno));
  49. 		return 0;
  50. 	}
  51.  
  52. 	errno = errno_save;
  53. 	return n;
  54. }
  55.  
  56. int
  57. main(void)
  58. {
  59. 	const char *s = "123hello";
  60. 	int n;
  61.  
  62.     fprintf(stderr, "[====atoi()====]\n");
  63. 	n = str_to_int_atoi(s);
  64. 	printf("        n: %d\nerrno set: %s\n\n", n, errno != 0 ? "Yes" : "No");
  65.  
  66. 	errno = 0;
  67.  
  68.     fprintf(stderr, "[===strtol()===]\n");
  69. 	n = str_to_int_strtol(s);
  70. 	printf("        n: %d\nerrno set: %s\n\n", n, errno != 0 ? "Yes" : "No");
  71.  
  72. 	return 0;
  73. }
Success #stdin #stdout #stderr 0s 2008KB
comments (?)
stdin
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Standard input is empty
stdout
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        n: 123
errno set: No

        n: 0
errno set: Yes
stderr
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[====atoi()====]
[===strtol()===]
strtol() error: operand "123hello": Invalid argument
https://ideone.com/aarpnh
language:
C (gcc 8.3)
created:
10 years ago
visibility:
public

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