URLDownloadToFile 总是返回 S_OK

Question

我是 C++ 新手，尝试编写一个更新函数。

使用 URLDownloadToFile 下载没有问题，但如果我将 url 更改为无效的，它仍然返回 S_OK ...我如何检查下载是否成功？

#include <WinInet.h>
#include <iomanip> 

int download_file (const TCHAR urldownload[],const TCHAR target[] )
{
    DownloadProgress progress;
    IBindStatusCallback* callback = (IBindStatusCallback*)&progress;

    SCP(40, NULL); cout << target;

    HRESULT status = URLDownloadToFile(NULL, urldownload, target, 0, static_cast<IBindStatusCallback*>(&progress));
    Sleep(200);
    DeleteUrlCacheEntry(urldownload);

    wcout << status;

    if (status == S_OK) cout << "yes";
    else(cout << "Download failed");

    Sleep(10000); return 1;
}


class DownloadProgress : public IBindStatusCallback {
public:
HRESULT __stdcall QueryInterface(const IID &, void **) {
    return E_NOINTERFACE;
}
ULONG STDMETHODCALLTYPE AddRef(void) {
    return 1;
}
ULONG STDMETHODCALLTYPE Release(void) {
    return 1;
}
HRESULT STDMETHODCALLTYPE OnStartBinding(DWORD dwReserved, IBinding *pib) {
    return E_NOTIMPL;
}
virtual HRESULT STDMETHODCALLTYPE GetPriority(LONG *pnPriority) {
    return E_NOTIMPL;
}
virtual HRESULT STDMETHODCALLTYPE OnLowResource(DWORD reserved) {
    return S_OK;
}
virtual HRESULT STDMETHODCALLTYPE OnStopBinding(HRESULT hresult, LPCWSTR szError) {
    return E_NOTIMPL;
}
virtual HRESULT STDMETHODCALLTYPE GetBindInfo(DWORD *grfBINDF, BINDINFO *pbindinfo) {
    return E_NOTIMPL;
}
virtual HRESULT STDMETHODCALLTYPE OnDataAvailable(DWORD grfBSCF, DWORD dwSize, FORMATETC *pformatetc, STGMEDIUM *pstgmed) {
    return E_NOTIMPL;
}
virtual HRESULT STDMETHODCALLTYPE OnObjectAvailable(REFIID riid, IUnknown *punk) {
    return E_NOTIMPL;
}

virtual HRESULT __stdcall OnProgress(ULONG ulProgress, ULONG ulProgressMax, ULONG ulStatusCode, LPCWSTR szStatusText)
{
    //wcout << ulProgress << L" of " << ulProgressMax << endl; Sleep(200);
    if (ulProgress != 0 && ulProgressMax != 0)
    {
        double output = (double(ulProgress) / ulProgressMax)*100;
        cout << "\r" << "Downloading: " << fixed << setprecision(2) << output << " %  " ; Sleep(20);
    }
    return S_OK;
}
};

Answer 1

MSDN article has the answer给你：

URLDownloadToFile 会返回S_OK，即使无法创建文件并取消下载。如果szFileName参数中包含文件路径，调用URLDownloadToFile前确保目标目录存在。为了更好地控制下载及其进度，推荐使用IBindStatusCallback 界面。

您需要提供一个状态回调来接收异步操作的状态。您的代码 sn-p 已经有了基础。 OnProgress 和 OnStopBinding 应该会给你下载失败的结果。