libcurl库的使用(通过libcurl库下载url图像) 【转】

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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 <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 ");
        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 ");
        return false;
    }

    CURL* curlCtx = curl_easy_init();
    curl_easy_setopt(curlCtx, CURLOPT_URL, url);

　 curl_easy_perform(curlCtx);
    char* ctbuf = NULL;
    if ( curl_easy_getinfo(curlCtx, CURLINFO_CONTENT_TYPE, &ctbuf) == 0 && ctbuf )
    {// image/jpeg
         if (strcmp(ctbuf,"image/jpeg")==0)
              isJpeg = true;
    }
    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 ", 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 ", 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";

    bool isJpeg = false;

    curl = curl_easy_init();
    if (curl) {
       curl_easy_setopt(curl, CURLOPT_URL, url);
        res = curl_easy_perform(curl);
        char* ctbuf = NULL;
        if ( curl_easy_getinfo(curl, CURLINFO_CONTENT_TYPE, &ctbuf) == 0 && ctbuf )
        {// image/jpeg
            if (strcmp(ctbuf,"image/jpeg")==0)
                isJpeg = true;
        }

        fp = fopen(outfilename, "wb");　　　　
        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 ");
        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_jpeg3(url)) {
        printf("!! Failed to download file: %s ", url);
        return -1;
    }
#else
    if (!download_jpeg2(url)) {
        printf("!! Failed to download file: %s ", url);
        return -1;
    }
#endif

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

// 补充第3种方式： 先将数据写到字符串中，然后再写成图像文件

char* url = "http://t0.tianditu.com/img_c/wmts/wmts?Service=WMTS&Request=GetTile&Version=1.0.0&Style=Default&Format=tiles&serviceMode=KVP&layer=img&TileMatrixSet=c&TileMatrix=1&TileRow=0&TileCol=0";    
   

long writer2(void *data, long size, int nmemb, void* lpVoid)
{
    std::string* content = dynamic_cast<std::string*>((std::string*)lpVoid);  
    long sizes = size * nmemb;
    //string temp;
    //temp = std::string((char*)data,sizes);
    //content += temp;
    content->append((char*)data,sizes);  
    return sizes;
}

bool CGlbGlobe::download_jpeg3(char* url)
{
    CURL *curl;
    CURLcode res;    
    std::string content;

    bool isJpeg = false;
    curl = curl_easy_init();
    if (curl) {        
        curl_easy_setopt(curl, CURLOPT_URL, url);        
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writer2);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&content);        
        res = curl_easy_perform(curl);

        char* ctbuf = NULL;
        if ( curl_easy_getinfo(curl, CURLINFO_CONTENT_TYPE, &ctbuf) == 0 && ctbuf )
        {// image/jpeg
            if (strcmp(ctbuf,"image/jpeg")==0)
                isJpeg = true;
        }
        long retcode = 0;
        res = curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE , &retcode);
        if ( (res == CURLE_OK) && retcode == 200 )
        {
            double length = 0;
            res = curl_easy_getinfo(curl, CURLINFO_CONTENT_LENGTH_DOWNLOAD , &length);
            printf("%d",retcode);
            FILE * file = fopen("out2.jpg","wb");
            fseek(file,0,SEEK_SET);
            fwrite(content.c_str(),1,length,file);
            fclose(file);
        }

        /* always cleanup */
        curl_easy_cleanup(curl);        
    }
    else {
        printf("!!!curl init failed ");
        return false;
    }
    return true;
}