Get a response into memory
This example is a variation of the former that instead of sending the received data to stdout (which often is not what you want), this example instead stores the incoming data in a memory buffer that is enlarged as the incoming data grows.
It accomplishes this by using a write callback to receive the data.
This example uses a fixed URL string with a set URL scheme, but you can of course change this to use any other supported protocol and then get a resource from that instead.
#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 = 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_handle;
CURLcode res;
struct MemoryStruct chunk;
chunk.memory = malloc(1); /* will be grown as needed by the realloc above */
chunk.size = 0; /* no data at this point */
/* init the curl session */
curl_handle = curl_easy_init();
/* specify URL to get */
curl_easy_setopt(curl_handle, CURLOPT_URL, "");
/* send all data to this function */
curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
/* we pass our 'chunk' struct to the callback function */
curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, (void *)&chunk);
/* some servers do not like requests that are made without a user-agent
field, so we provide one */
curl_easy_setopt(curl_handle, CURLOPT_USERAGENT, "libcurl-agent/1.0");
/* get it! */
res = curl_easy_perform(curl_handle);
/* check for errors */
if(res != CURLE_OK) {
fprintf(stderr, "curl_easy_perform() failed: %s\n",
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("%lu bytes retrieved\n", (long)chunk.size);
/* cleanup curl stuff */
/* we are done with libcurl, so clean it up */
return 0;
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