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  1. #include <errno.h>
  2. #include <assert.h>
  3. #include <inttypes.h>
  4. #include <locale.h>
  5. #include <stdio.h>
  6. #include <stdlib.h>
  7. #include <string.h>
  8.  
  9. int safe_atou(const char *s, unsigned *ret_u) {
  10.         char *x = NULL;
  11.         unsigned long l;
  12.  
  13.         assert(s);
  14.         assert(ret_u);
  15.  
  16.         /* strtoul() is happy to parse negative values, and silently
  17.          * converts them to unsigned values without generating an
  18.          * error. We want a clean error, hence let's look for the "-"
  19.          * prefix on our own, and generate an error. But let's do so
  20.          * only after strtoul() validated that the string is clean
  21.          * otherwise, so that we return EINVAL preferably over
  22.          * ERANGE. */
  23.  
  24.  
  25.         errno = 0;
  26.         l = strtoul(s, &x, 0);
  27.         if (errno > 0)
  28.                 return -errno;
  29.         if (!x || x == s || *x)
  30.                 return -EINVAL;
  31.         if (s[0] == '-')
  32.                 return -ERANGE;
  33.         if ((unsigned long) (unsigned) l != l)
  34.                 return -ERANGE;
  35.  
  36.         *ret_u = (unsigned) l;
  37.         return 0;
  38. }
  39.  
  40. int main(void) {
  41.     unsigned res = 1337;
  42.     const char *tests[] = {"0day", "day0", "42", "-0", "-1", "0", "1337", "0p3nn3t", 0};
  43.     const char **test = tests;
  44.     while (*test) {
  45.         int err = safe_atou(*test, &res);
  46.         printf("\ninput: %.6s, err: %d, val: %i", *test, err, res);
  47.         test++;
  48.     }
  49.  
  50. }
  51.  
  52.  
Success #stdin #stdout 0s 9432KB
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stdin
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Standard input is empty
stdout
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input: 0day, err: -22, val: 1337
input: day0, err: -22, val: 1337
input: 42, err: 0, val: 42
input: -0, err: -34, val: 42
input: -1, err: -34, val: 42
input: 0, err: 0, val: 0
input: 1337, err: 0, val: 1337
input: 0p3nn3, err: -22, val: 1337
https://ideone.com/SEriLl
language:
C (gcc 8.3)
created:
6 years ago
visibility:
public

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