#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#if defined(__APPLE__)
#  define COMMON_DIGEST_FOR_OPENSSL
#  include <CommonCrypto/CommonDigest.h>
#  define SHA1 CC_SHA1
#else
#  include <openssl/md5.h>
#endif

char *str2md5(const char *str, int length) {
   int n;
   MD5_CTX c;
   unsigned char digest[16];
   char *out = (char*)malloc(33);

   MD5_Init(&c);

   while (length > 0) {
        if (length > 512) {
            MD5_Update(&c, str, 512);
        } else {
            MD5_Update(&c, str, length);
        }
        length -= 512;
        str += 512;
     }

     MD5_Final(digest, &c);

     for (n = 0; n < 16; ++n) {
     snprintf(&(out[n*2]), 16*2, "%02x", (unsigned int)digest[n]);
     }

    return out;
 }

   int main(int argc, char **argv) {
       char *output = str2md5("hello", strlen("hello"));
       printf("%sn", output);
       free(output);
        return 0;
    }