使用libcurl下载文件小例

#include "curl.h"  
#ifdef _DEBUG  
#pragma comment(lib, "../Debug/libcurld")  
#else  
#pragma comment(lib, "../Release/libcurl")  
#endif  

<pre name="code" class="cpp">// UseLibCurl.cpp : 定义控制台应用程序的入口点。  
//  
  
#include "stdafx.h"  
#include <Windows.h>  
#include <CommCtrl.h>  
#include "resource.h"  
#include "curl.h"  
#ifdef _DEBUG  
#pragma comment(lib, "../Debug/libcurld")  
#else  
#pragma comment(lib, "../Release/libcurl")  
#endif  
  
  
//这个用来保存对话框的窗口句柄，因为后面要向这个窗口发消息，必须知道其窗口句柄  
HWND    g_hDlgWnd = NULL;  
//提供给CURL下载进度回调的函数，用于保存下载的数据到文件  
static size_t   DownloadCallback(void* pBuffer, size_t nSize, size_t nMemByte, void* pParam);  
//提供给CURL下载进度回调的函数，用于计算下载进度通知界面  
static int ProgressCallback(void *clientp, double dltotal, double dlnow, double ultotal, double ulnow);  
//这是对话框的消息循环，在控制台程序里面创建GUI，仅仅是为了更好地展现下载回调这个功能  
INT_PTR CALLBACK DialogProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);  
//这个是下载的线程函数，为了不把对话框主界面卡死，肯定是要自己开线程来下载的了  
DWORD WINAPI DownloadThread(LPVOID lpParam);  
  
int _tmain(int argc, _TCHAR* argv[])  
{  
    //弹出对话框，知道对话框关闭才会执行退出  
    DialogBox(NULL, MAKEINTRESOURCE(IDD_DIALOG1), NULL, DialogProc );  
    return 0;  
}  
  
static size_t DownloadCallback(void* pBuffer, size_t nSize, size_t nMemByte, void* pParam)  
{  
    //把下载到的数据以追加的方式写入文件(一定要有a，否则前面写入的内容就会被覆盖了)  
    FILE* fp = NULL;  
    fopen_s(&fp, "c:\\test.apk", "ab+");  
    size_t nWrite = fwrite(pBuffer, nSize, nMemByte, fp);  
    fclose(fp);  
    return nWrite;  
}  
  
static int ProgressCallback(void *clientp, double dltotal, double dlnow, double ultotal, double ulnow)  
{  
    if ( dltotal > -0.1 && dltotal < 0.1 )  
        return 0;  
    int nPos = (int) ( (dlnow/dltotal)*100 );  
    //通知进度条更新下载进度  
    ::PostMessage(g_hDlgWnd, WM_USER + 110, nPos, 0);  
    //::Sleep(10);  
    return 0;  
}  
  
INT_PTR CALLBACK DialogProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)  
{  
    switch( uMsg )  
    {  
    case WM_INITDIALOG:  
        {  
            g_hDlgWnd = hWnd;  
            HWND hProgress = GetDlgItem(hWnd, IDC_PROGRESS1);  
            SendMessage(hProgress, PBM_SETRANGE32, (WPARAM) 0, (LPARAM) 100);  
            //对话框初始化时创建下载线程  
            HANDLE hThread = CreateThread(NULL, 0, DownloadThread, 0, 0, NULL);  
            CloseHandle(hThread);  
            ::SetWindowText(hWnd, L"使用CURL下载文件示例：");  
            return TRUE;  
        }  
    case WM_COMMAND:  
        {  
            WORD  msg = HIWORD(wParam);  
            WORD  id  = LOWORD(wParam);  
            if ( id == IDOK || id == IDCANCEL )  
                EndDialog(hWnd, id);  
            break;  
        }  
    case WM_ERASEBKGND:  
        return TRUE;  
    case WM_CTLCOLORSTATIC:  
        return (INT_PTR)(HBRUSH)::GetStockObject(WHITE_BRUSH);  
    case WM_USER + 110:  
        {//接收到设置进度的消息  
            HWND    hProgress   = GetDlgItem(hWnd, IDC_PROGRESS1);  
            HWND    hStatus     = GetDlgItem(hWnd, IDC_STATUS);  
            if ( hProgress )  
                SendMessage(hProgress, PBM_SETPOS, wParam, 0L);  
            if ( hStatus )  
            {  
                WCHAR szBuffer[100] = {0};  
                if ( wParam<100 )  
                    swprintf(szBuffer, L"正在下载文件，进度：%d%%", wParam);  
                else  
                    swprintf(szBuffer, L"文件下载完毕！");  
                ::SetWindowText(hStatus, szBuffer);  
            }  
            return 0;  
        }  
    default:  
        break;  
    }  
    return DefWindowProc(hWnd, uMsg, wParam, lParam);  
}  
  
DWORD WINAPI DownloadThread(LPVOID lpParam)  
{  
    //初始化curl，这个是必须的  
    CURL* curl = curl_easy_init();  
    curl_easy_setopt(curl, CURLOPT_URL, "http://android.shoujids.com/software/download?id=154103");  
    //设置接收数据的回调  
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, DownloadCallback);  
    //curl_easy_setopt(curl, CURLOPT_INFILESIZE, lFileSize);  
    //curl_easy_setopt(curl, CURLOPT_HEADER, 1);  
    //curl_easy_setopt(curl, CURLOPT_NOBODY, 1);  
    //curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);  
    // 设置重定向的最大次数  
    curl_easy_setopt(curl, CURLOPT_MAXREDIRS, 5);  
    // 设置301、302跳转跟随location  
    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1);  
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);  
    //设置进度回调函数  
    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, ProgressCallback);  
    //curl_easy_getinfo(curl,  CURLINFO_CONTENT_LENGTH_DOWNLOAD, &lFileSize);  
    //curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, g_hDlgWnd);  
    //开始执行请求  
    CURLcode retcCode = curl_easy_perform(curl);  
    //查看是否有出错信息  
    const char* pError = curl_easy_strerror(retcCode);  
    //清理curl，和前面的初始化匹配  
    curl_easy_cleanup(curl);  
    return 0;  
}