curl返回值写入内存的场景

#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 + 1);
if(mem->memory == NULL) {
/* out of memory! */
printf("not enough memory (realloc returned NULL)\n");
return 0;
}

memcpy(&(mem->memory[mem->size]), contents, realsize);
mem->size += realsize;
mem->memory[mem->size] = 0;

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(1);  /* will be grown as needed by realloc above */
chunk.size = 0;    /* 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 0;
}