Get ParamKey From URL Query String, this is derived from https://github.com/Taymindis/fcgi-function

get_param_key.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>


int strpos(const char *haystack, const char *needle)
{
   char *p = strstr(haystack, needle);
   if (p)
      return p - haystack;
   return -1;   // Not found = -1.
}

void* csif_getParam(const char *key, const char* query_str) {
   int len, pos;
   char *qs = query_str;
   if (key && *key && qs && *qs) {
      len = strlen(key);
      do {
         if ((pos = strpos(qs, key)) < 0) return NULL;

         if (pos == 0 || qs[pos - 1] == '&') {
            qs = (char*)qs + pos + len;
            if (*qs++ == '=') {
               char *src = qs,
                     *ret;
               size_t sz = 0;
               while (*qs && *qs++ != '&')sz++;

               ret = malloc(sz + 1);
               memset(ret, 0, sz + 1);
               return memcpy(ret, src, sz);
            } else while (*qs && *qs++ != '&');
         } else while (*qs && *qs++ != '&');
      } while (*qs);
   }
   return NULL;
}

int main ()
{
   const char str1[] = "keyword=GHI&userId2=20&userId=100&userId3=S@102130";
   const char str2[] = "my_id";

   char* found = csif_getParam("keyword", str1);

   char* found2 = csif_getParam("userId2", str1);
   char* found3 = csif_getParam("userId", str1);
   if (found) {
      printf("%s\n", found);
      free(found);

      found = csif_getParam("userId3", str1);
      if (found) {
         printf("%s\n", found);
         free(found);
      }
   }
   if (found2) {
      printf("%s\n", found2);
      free(found2);
   }

   if (found3) {
      printf("%s\n", found3);

      free(found3);
   }

   return (0);
}