c - Does free() set errno? -

if buf malloc() allocated char buffer, free(buf) set/reset errno?

let's want write buffer file, , free it, don't need more.

let's error policy code return -1 on error.

is proper way write out buffer , error check without leaking memory?

fputs(buf, somefile); free(buf); if (errno) return -1; 

or need consider free possibly setting errno, in...

fputs(buf, somefile); if (errno){      free(buf);     return -1; } free(buf); 

or, horror of horrors,

do {    fputs(buf, somefile);   int save_errno = errno;   free(buf);   errno = save_errno;   if (errno) return -1; } while(0);   

where use of block allows local save_errno exist in various places should need reused.

all of seem depend on whether free() sets errno.

the linux man page free() man page malloc(), etc. mentions malloc() setting errno, not free().

the gnu c library manual page freeing dynamic memory not mention whether free() sets errno.

so wrote short program force write error see if free() reset errno, , not. i'm wondering if should rely upon result , fact free() essential "of course doesn't set errno."

# see if free() resets errno on bad write #include <errno.h> #include <stdio.h> #include <stdlib.h> #include <string.h>  int main(int argc, char **argv) {   char * buf = malloc(256);   snprintf(buf,256,"%s\n", "hello, world!");    file *badfile;    badfile = fopen("/dev/null","r");    fputs(buf, badfile);   free(buf);   printf("%d\n", errno);   printf("%s\n", strerror(errno)); } 

posix doesn't define free set errno (although posix doesn't forbid it, implementation might - refer @arjunshankar's answer more details). that's not relevant concern.

the way you're checking errors incorrect. should check return value of fputs, , check if it's smaller 0. if is, can check errno find out caused failure, that's optional (and should done before calling further functions).

so, should trick :

int result = fputs(buf, somefile); /* optionally read errno here if result < 0 (before free call) */ free(buf); return (result < 0) ? -1 : 0;