libcurl库的使用(通过libcurl库下载url图像)

1. 从http://curl.haxx.se/download.html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 <iostream>
#include <curl/curl.h>

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 = "http://f.hiphotos.baidu.com/image/pic/item/d043ad4bd11373f0671f5d95a60f4bfbfbed0493.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;
}

参考文献：

1. http://stackoverflow.com/questions/10112959/download-an-image-from-server-curl-however-taking-suggestions-c

2. http://stackoverflow.com/questions/1636333/download-file-using-libcurl-in-c-c

3. https://www.hackthissite.org/articles/read/1078

4. http://curl.askapache.com/c/example.html

GitHub：https://github.com/fengbingchun/Libcurl_Test