在C++中，可以有以下两种办法

使用COM接口IThumbnailCache

文档链接：IThumbnailCache (thumbcache.h) - Win32 apps | Microsoft Learn

示例代码如下：

VOID GetFileThumbnail(PCWSTR path)
{HRESULT hr = CoInitialize(nullptr);IShellItem* item = nullptr;hr = SHCreateItemFromParsingName(path, nullptr, IID_PPV_ARGS(&item));IThumbnailCache* cache = nullptr;hr = CoCreateInstance(CLSID_LocalThumbnailCache,nullptr,CLSCTX_INPROC,IID_PPV_ARGS(&cache));WTS_CACHEFLAGS flags = WTS_LOWQUALITY;ISharedBitmap* shared_bitmap;hr = cache->GetThumbnail(item,12*16,WTS_EXTRACT,&shared_bitmap,nullptr,nullptr);HBITMAP hbitmap = NULL;hr = shared_bitmap->GetSharedBitmap(&hbitmap);shared_bitmap->Release();cache->Release();CoUninitialize();//使用hbitmap，使用完成后调用DeleteObjectDeleteObject(hbitmap);}

前面我一直使用的这种方式，但是最近系统升级后，会报 Generic Error in GDI+ 

后面我升级成了下面这种方式

使用IShellItemImageFactory接口

文档链接：IShellItemImageFactory (shobjidl_core.h) - Win32 apps | Microsoft Learn

官方示例代码：Windows-classic-samples/Samples/Win7Samples/winui/shell/appplatform/UsingImageFactory/ImageFactorySample.cpp at main · microsoft/Windows-classic-samples · GitHub

HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);HBITMAP hbmp = NULL;if (SUCCEEDED(hr)){IShellItemImageFactory* pImageFactory;hr = SHCreateItemFromParsingName(path, NULL, IID_PPV_ARGS(&pImageFactory));if (SUCCEEDED(hr)){SIZE size = { 256, 256 };  //图像大小hr = pImageFactory->GetImage(size, SIIGBF_THUMBNAILONLY, &hbmp);pImageFactory->Release();}CoUninitialize();//使用hbmp,使用完成后调用DeleteObjectDeleteObject(hbmp);}

在C#中使用，可以直接nuget引用  WindowsAPICodePack-Shell  包

PM> NuGet\Install-Package WindowsAPICodePack-Shell -Version 1.1.1

然后用下面的代码就可以获取文件缩略图

ShellFile shellFile = ShellFile.FromFilePath(filepath);
Bitmap shellThumb = shellFile.Thumbnail.ExtraLargeBitmap;