libcurl库的使用(通过libcurl库下载url图像)

1. 从这里下载libcurl源码，解压缩；

2. 通过CMake(cmake-gui)生成vs2013 x64位 CURL.sln；

3. 打开CURL.sln，编译会生成libcurl.dll动态库；

4. 在CURL.sln基础上，添加一个testlibcurl控制台工程；

5. testlibcurl.cpp：

#include "stdafx.h"
#include
#include

size_t callbackfunction(void *ptr, size_t size, size_t nmemb, void* userdata)
{
? ? FILE* stream = (FILE*)userdata;
? ? if (!stream) {
? ? ? ? printf("!!! No stream\n");
? ? ? ? return 0;
? ? }

? ? size_t written = fwrite((FILE*)ptr, size, nmemb, stream);
? ? return written;
}

bool download_jpeg(char* url)
{
? ? FILE* fp = fopen("out.jpg", "wb");
? ? if (!fp) {
? ? ? ? printf("!!! Failed to create file on the disk\n");
? ? ? ? return false;
? ? }

? ? CURL* curlCtx = curl_easy_init();
? ? curl_easy_setopt(curlCtx, CURLOPT_URL, url);
? ? curl_easy_setopt(curlCtx, CURLOPT_WRITEDATA, fp);
? ? curl_easy_setopt(curlCtx, CURLOPT_WRITEFUNCTION, callbackfunction);
? ? curl_easy_setopt(curlCtx, CURLOPT_FOLLOWLOCATION, 1);

? ? CURLcode rc = curl_easy_perform(curlCtx);
? ? if (rc) {
? ? ? ? printf("!!! Failed to download: %s\n", url);
? ? ? ? return false;
? ? }

? ? long res_code = 0;
? ? curl_easy_getinfo(curlCtx, CURLINFO_RESPONSE_CODE, &res_code);
? ? if (!((res_code == 200 || res_code == 201) && rc != CURLE_ABORTED_BY_CALLBACK)) {
? ? ? ? printf("!!! Response code: %d\n", res_code);
? ? ? ? return false;
? ? }

? ? curl_easy_cleanup(curlCtx);
? ? fclose(fp);

? ? return true;
}

size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream)
{
? ? size_t written = fwrite(ptr, size, nmemb, stream);
? ? return written;
}

bool download_jpeg2(char* url)
{
? ? CURL *curl;
? ? FILE *fp;
? ? CURLcode res;
? ? char* outfilename = "out2.jpg";

? ? curl = curl_easy_init();
? ? if (curl) {
? ? ? ? fp = fopen(outfilename, "wb");
? ? ? ? curl_easy_setopt(curl, CURLOPT_URL, url);
? ? ? ? curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
? ? ? ? curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
? ? ? ? res = curl_easy_perform(curl);
? ? ? ? /* always cleanup */
? ? ? ? curl_easy_cleanup(curl);
? ? ? ? fclose(fp);
? ? }
? ? else {
? ? ? ? printf("!!!curl init failed\n");
? ? ? ? return false;
? ? }

? ? return true;
}

int main(int argc, char* argv[])
{
? ? char* url = "https://www.cppentry.com/upload_files/article/54/1_g14ha__.jpg";

#if 1
? ? if (!download_jpeg(url)) {
? ? ? ? printf("!! Failed to download file: %s\n", url);
? ? ? ? return -1;
? ? }
#else
? ? if (!download_jpeg2(url)) {
? ? ? ? printf("!! Failed to download file: %s\n", url);
? ? ? ? return -1;
? ? }
#endif

? ? std::cout << "ok!" << std::endl;
?return 0;
}