#define _GNU_SOURCE
#include <string.h>

char* strsep(char** str, const char* sep) {
    char *s = *str, *end;
    if (!s)
        return NULL;
    end = s + strcspn(s, sep);
    if (*end)
        *end++ = 0;
    else
        end = 0;
    *str = end;
    return s;
}