在c語言中，有時候我們需要從url中獲取傳過來的json數據，這時候我們可以使用一些常見的庫來實現這個功能。

#include#include#include#includestruct 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);
chunk.size = 0;
/* 初始化curl */
curl_global_init(CURL_GLOBAL_ALL);
/* 初始化一個curl比手動賦值快得多 */
curl_handle = curl_easy_init();
/* 設置url */
curl_easy_setopt(curl_handle, CURLOPT_URL, "https://jsonplaceholder.typicode.com/todos/1");
/* 設置http請求頭 */
struct curl_slist *headers = NULL;
headers = curl_slist_append(headers, "Content-Type: application/json");
curl_easy_setopt(curl_handle, CURLOPT_HTTPHEADER, headers);
/* 設置回調函數 */
curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
/* 將回調函數數據交給curl */
curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, (void *)&chunk);
/* 執行curl請求 */
res = curl_easy_perform(curl_handle);
/* 檢查curl請求是否成功 */
if (res != CURLE_OK) {
fprintf(stderr, "curl_easy_perform() failed: %s\n",
curl_easy_strerror(res));
} else {
printf("%s\n", chunk.memory);
}
/* 清理curl資源 */
curl_easy_cleanup(curl_handle);
/* 清理http請求頭資源 */
curl_slist_free_all(headers);
/* 釋放回調函數數據 */
free(chunk.memory);
/* 清理全局curl資源 */
curl_global_cleanup();
return 0;
}

上面的代碼中，我們先使用curl_global_init()初始化curl，然后初始化一個curl_easy_init()，設置url和http請求頭，接著設置一個回調函數，最后執行curl請求并檢查請求是否成功。我們可以在回調函數中查看是否獲取到json數據。