If perror is not flexible enough, you may obtain a user-readable error description by calling strerror from <string.h>.

int main(int argc, char *argv[])
{
    FILE *fout;
    int last_error = 0;

    if ((fout = fopen(argv[1], "w")) == NULL) {
        last_error = errno;
         /* reset errno and continue */
         errno = 0;
    }

    /* do some processing and try opening the file differently, then */

if (last_error) {
    fprintf(stderr, "fopen: Could not open %s for writing: %s", 
            argv[1], strerror(last_error));
    fputs("Cross fingers and continue", stderr);
}

/* do some other processing */

return EXIT_SUCCESS;
}