libcur设置接收数据的回调函数以及回调函数的使用

            curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, OnWriteData);

            curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&strResponse);

LibCurl设置读取数据的回调函数

//lpVoid 是CURLOPT_WRITEDATA设置的缓冲区指针,buffer是libcurl内部的数据缓冲区,注意

如果读取的网页或数据特别大,那么这个函数会多次调用,所以数据必须累加起来.如下结构调用了

  str->append(pData, size * nmemb);

size是数据类型的大小,如sizeof(char),

nmemb是数据的大小.这个和fwrite等写文件的参数类似

传入的lpVoid可以是字符串,char *,或者是文件句柄.在这儿回调里面处理数据.如下面downLoadPackage

size_t CHttpClient::OnWriteData(void* buffer, size_t size, size_t nmemb, void* lpVoid)

{

            std::string* str = dynamic_cast<std::string*>((std::string *)lpVoid);

            if (NULL == str || NULL == buffer)

            {

                        return -1;

            }

            char* pData = (char*)buffer;

            str->append(pData, size * nmemb);

            return nmemb;

}

size_t CHttpClient::downLoadPackage(void *buffer , size_t size, size_t nmemb, void *lpVoid )

{

            FILE *fp = (FILE*)lpVoid ;

            size_t written = fwrite(buffer , size, nmemb, fp);

            return written;

}