c - What is the correct behavior of strtol? -

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i'm creating wrapper function around strtol() int16_t, , ran across problem: how handle input such 0x? is, valid digit 0, followed non-digit x, or invalid because nothing follows 0x?

tl;dr results: windows rejects 0x described in latter case, debian sees digit 0, followed non-digit character x, explained in former case.

implementations tested1

  • windows
    • visual c++ 2015 (henceforth msvc)
    • mingw-w64 gcc (5.2.0)
  • debian

for further comparison purposes, included sscanf() format specification of " %li", supposed act strtol() base==0. surprisingly, ended 2 different results.

code:

#include <errno.h> #include <stdio.h> #include <stdlib.h> #include <string.h>  int main(void) {     const char *foo = "        0x";     char *remainder;     long n;     int base = 0;      n = strtol(foo, &remainder, base);     printf("strtol(): ");     if (*remainder == 'x')         printf("ok\n");     else {         printf("nomatch\n");         printf("  remaining -- %s\n", remainder);         printf("  errno: %s (%d)\n", strerror(errno), errno);     }      errno = 0;      base = sscanf(foo, " %li", &n);     printf("sscanf(): ");     if (base == 1)         printf("ok\n");     else {         printf("nomatch\n");         printf("  returned: %s\n", base==0 ? "0" : "eof");         printf("  errno: %s (%d)\n", strerror(errno), errno);     } }

debian results:

strtol(): ok sscanf(): ok

windows results:

strtol(): nomatch   remaining --         0x   errno: no error (0) sscanf(): nomatch   returned: 0   errno: no error (0)

there no error in case, yet results differed. initializing base 16 instead of 0 made no difference @ all, nor did removal of leading blanks in test string.

i expected result got on debian: 0 parsed valid value (whether base 0 or 16), , remainder set point x after seeing there no valid hexadecimal values following x (had there been any, 0x skipped whether base 0 or 16).

so i'm confused correct behavior in situation. either of these behaviors in violation of c standard? interpretation of relevant sections of standard debian correct, i'm not certain.

1 cygwin exhibited windows behavior in case of strtol() , debian behavior in case of sscanf() interested. since behavior of %li supposed match strtol() base==0, considered bug , ignored results.

the specification 7.22.1.4 of c11:

  1. if value of base zero, expected form of subject sequence of integer constant described in 6.4.4.1,

  2. the subject sequence defined longest initial subsequence of input string, starting first non-white-space character, of expected form

as described in 6.4.4.1, 0 integer constant, 0x not. therefore, subject sequence 0 input case.

so correct behaviour return 0, , endptr should left pointing x.


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