curl返回值写入内存的场景

直接上代码：

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

 struct MemoryStruct {
   char *memory;
   size_t size;
 };

 static size_t
 WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
 {
   size_t realsize = size * nmemb;
   struct MemoryStruct *mem = (struct MemoryStruct *)userp;

   mem->memory = (char*)realloc(mem->memory, mem->size + realsize + );
   if(mem->memory == NULL) {
     /* out of memory! */
     printf("not enough memory (realloc returned NULL)\n");
     return ;
   }

   memcpy(&(mem->memory[mem->size]), contents, realsize);
   mem->size += realsize;
   mem->memory[mem->size] = ;

   return realsize;
 }
 int main(void)
 {
   CURL *curl;
   CURLcode res;
   struct MemoryStruct chunk;
   static const char *postthis="Field=1&Field=2&Field=3";

   chunk.memory = (char*)malloc();  /* will be grown as needed by realloc above */
   chunk.size = ;    /* no data at this point */

   curl_global_init(CURL_GLOBAL_ALL);
   curl = curl_easy_init();
   if(curl) {

     curl_easy_setopt(curl, CURLOPT_URL, "http://www.example.org/");

     /* send all data to this function  */
     curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);

     /* we pass our 'chunk' struct to the callback function */
     curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);

     /* some servers don't like requests that are made without a user-agent
        field, so we provide one */
     curl_easy_setopt(curl, CURLOPT_USERAGENT, "libcurl-agent/1.0");

     curl_easy_setopt(curl, CURLOPT_POSTFIELDS, postthis);

     /* if we don't provide POSTFIELDSIZE, libcurl will strlen() by
        itself */
     curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, (long)strlen(postthis));

     /* Perform the request, res will get the return code */
     res = curl_easy_perform(curl);
     /* Check for errors */
     if(res != CURLE_OK) {
       fprintf(stderr, "curl_easy_perform() failed: %s\n",
               curl_easy_strerror(res));
     }
     else {
       /*
        * Now, our chunk.memory points to a memory block that is chunk.size
        * bytes big and contains the remote file.
        *
        * Do something nice with it!
        */
       printf("%s\n",chunk.memory);
     }

     /* always cleanup */
     curl_easy_cleanup(curl);

     free(chunk.memory);

     /* we're done with libcurl, so clean it up */
     curl_global_cleanup();
   }
   return ;
 }