curl使用小记(三)——获取远端数据到内存缓冲区

#include <iostream>
#include <curl/curl.h>

using namespace std;

//内存块结构体
struct MemoryStruct
{
	char *memory;
	size_t size;

	MemoryStruct()
	{
		memory = (char *)malloc(1);
		size = 0;
	}

	~MemoryStruct()
	{
		free(memory);
		memory = NULL;
	}
};

//回调函数实现：一次请求可能多次调回调函数
size_t HttpPostWriteBack(void *contents, size_t size, size_t nmemb, void *userp)
{
	size_t realsize = size * nmemb;//一次回调返回的数据量
	struct MemoryStruct *mem = (struct MemoryStruct *)userp;

	char *ptr = (char *)realloc(mem->memory, mem->size + realsize);
	if (ptr == NULL)
	{
		printf("not enough memory (realloc returned NULL)\n");
		return 0;
	}

	mem->memory = ptr;
	memcpy(&(mem->memory[mem->size]), contents, realsize);
	mem->size += realsize;
	return realsize;//必须返回真实的数据
}

int main()
{
	const char *netlink = "http://cn.bing.com/th?id=OHR.GrandsCausses_EN-CN3335882379_800x480.jpg";
	const char *output = "D:/dst1.jpg";

	curl_global_init(CURL_GLOBAL_ALL);		//初始化全局资源

	CURL *curl = curl_easy_init();		//初始化句柄

	//需要的话，可以设置代理
	//curl_easy_setopt(curl, CURLOPT_PROXY, "127.0.0.1:7890");
	
	//访问网址
	curl_easy_setopt(curl, CURLOPT_URL, netlink);

	//设置用户代理
	curl_easy_setopt(curl, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.121 Safari/537.36");
	   
	//获取数据
	MemoryStruct chunk;	
	curl_easy_setopt(curl, CURLOPT_WRITEDATA, &chunk);
	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, HttpPostWriteBack);

	////实现下载进度
	//curl_easy_setopt(curl, CURLOPT_NOPROGRESS, false);
	//curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_callback);
	//curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, nullptr);

	//运行
	curl_easy_perform(curl);

	curl_easy_cleanup(curl);			//释放句柄

	curl_global_cleanup(); //释放全局资源

	//写出数据
	FILE *fp = nullptr;
	if (fopen_s(&fp, output, "wb") != 0)
	{
		curl_easy_cleanup(curl);
		return 0;
	}
	fwrite(chunk.memory, chunk.size, 1, fp);
	fclose(fp);

	return 1;
}