Having a sufficiently large static limit is probably good enough for all situations.
If you really need to get the entire error message, you can use the GNU version of strerror_r, or you can use the standard version
and poll it with successively larger buffers until you get what you need. For example,
you may use something like the code below.
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Call strerror_r and get the full error message. Allocate memory for the
* entire string with malloc. Return string. Caller must free string.
* If malloc fails, return NULL.
*/
char *all_strerror(int n)
{
char *s;
size_t size;
size = 1024;
s = malloc(size);
if (s == NULL)
return NULL;
while (strerror_r(n, s, size) == -1 && errno == ERANGE) {
size *= 2;
s = realloc(s, size);
if (s == NULL)
return NULL;
}
return s;
}
int main(int argc, char **argv)
{
for (int i = 1; i < argc; ++i) {
int n = atoi(argv[i]);
char *s = all_strerror(n);
printf("[%d]: %s\n", n, s);
free(s);
}
return 0;
}