test.c

char* segment(char *g, int m, int n) {
    char *r = (char*) malloc((n - m + 1) * sizeof(char));
    char *temp = g;

    temp += m;
    
    while (m != n) {
      r[m] = temp[m];
      m++;
    }
    
    r[m] = '\0';
    return r;
}

//segment("testtest", 0, 4) -> "test"