#include <stdio.h>

// start Nicks Hilfsmethoden

char *BCX_TmpStr(size_t Bites) {
    static int StrCnt;
    static char *StrFunc[64];
    StrCnt = (StrCnt + 1) & 63;
    free(StrFunc[StrCnt]);
    return StrFunc[StrCnt] = (char*) calloc(Bites + 256, 1);
}

char *replace(char *src, char *pat, char *rep) {
    size_t patsz, repsz, tmpsz, delta;
    char *strtmp, *p, *q, *r;
    if (!src)
        src = "";
    if (!pat || !*pat) {
        strtmp = BCX_TmpStr(strlen(src));
        if (!strtmp)
            return NULL;
        return strcpy(strtmp, src);
    }
    if (rep == NULL)
        rep = "";
    repsz = strlen(rep);
    patsz = strlen(pat);
    for (tmpsz = 0, p = src; q = strstr(p, pat); p = q + patsz)
        tmpsz += (size_t) (q - p) + repsz;
    tmpsz += strlen(p);
    strtmp = BCX_TmpStr(tmpsz);
    if (!strtmp)
        return NULL;
    for (r = strtmp, p = src; q = strstr(p, pat); p = q + patsz) {
        delta = (size_t) (q - p);
        strncpy(r, p, delta);
        r += delta;
        strcpy(r, rep);
        r += repsz;
    }
    strcpy(r, p);
    return strtmp;
}

// end Nicks Hilfsmethoden

int main(int argc, char *argv[]) {

    char* x = "wtf,halhalo,halo";

    char a[4096];
    strcpy(a, x);
    printf("%s\n", x);

    strcpy(a, (char*) replace(a, ",", "."));

    x = a;

    printf("%s\n", x);
    return 0; //  End of main program
}