scanf dynamic allocation

%m is a POSIX extension, which may be why it's not available in Pelles C.

There is an example in the man page for scanf/sscanf (page 3, from line 270-290) that states the following:

EXAMPLE

To use the dynamic allocation conversion specifier, specify m as a length modifier (thus %ms or %m[range]). The caller must free(3) the returned string, as in the following example:

char *p;
int n;

errno = 0;
n = scanf("%m[a-z]", &p);
if (n == 1) {
   printf("read: %s\n", p);
   free(p);
} else if (errno != 0) {
   perror("scanf");
} else {
   fprintf(stderr, "No matching characters\n");
}

As shown in the above example, it is necessary to call free(3) only if the scanf() call successfully read a string.

Source: SCANF(3) - Linux Programmer's Manual - GNU - 2013-01-30

I am not seeing %m in section 7.21.6.2 of the Draft C11 standard (the section on fscanf). I suggest that you avoid it and call malloc() as you would in C99.