c++ 创建一个窗口将base64图像展示在窗口上不使用qt 详细方法 不写入文件 使用GDI+

要在C++中创建一个窗口并将base64图像展示在窗口上，需要进行以下步骤：

1. 首先，需要使用GDI+库来处理图像，所以需要在代码中包含以下头文件：

#include <gdiplus.h>
#pragma comment (lib,"Gdiplus.lib")

2. 接着，需要创建一个窗口，可以使用Windows API的CreateWindow函数。示例代码如下：

HWND hwnd = CreateWindow("STATIC", NULL, WS_VISIBLE | WS_POPUP, 0, 0, 500, 500, NULL, NULL, NULL, NULL);

3. 然后，需要将base64图像解码为位图。可以使用GDI+的Bitmap类来完成。示例代码如下：

Gdiplus::Bitmap* bitmap;
std::string base64_image; // 假设已经有一个base64编码的图像字符串

std::vector<BYTE> data;
data.insert(data.end(), base64_image.begin(), base64_image.end());
data.push_back('\0');

DWORD size = 0;
BYTE* buffer = NULL;

if (::CryptStringToBinaryA(data.data(), data.size(), CRYPT_STRING_BASE64, buffer, &size, NULL, NULL)) {
    buffer = new BYTE[size];
    if (::CryptStringToBinaryA(data.data(), data.size(), CRYPT_STRING_BASE64, buffer, &size, NULL, NULL)) {
        IStream* stream = SHCreateMemStream(buffer, size);
        bitmap = Gdiplus::Bitmap::FromStream(stream);
        stream->Release();
    }
    delete[] buffer;
}

4. 最后，需要将位图绘制到窗口上。可以使用GDI+的Graphics类和HDC句柄来完成。示例代码如下：

PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);

Gdiplus::Graphics graphics(hdc);
graphics.DrawImage(bitmap, 0, 0, 500, 500);

EndPaint(hwnd, &ps);

完整代码示例：

#include <windows.h>
#include <gdiplus.h>
#include <vector>
#include <string>
#include <wincrypt.h>
#include <shlwapi.h>

#pragma comment (lib,"Gdiplus.lib")
#pragma comment (lib,"Crypt32.lib")
#pragma comment (lib,"Shlwapi.lib")

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    switch (msg) {
    case WM_PAINT: {
        Gdiplus::Bitmap* bitmap;
        std::string base64_image; // 假设已经有一个base64编码的图像字符串

        std::vector<BYTE> data;
        data.insert(data.end(), base64_image.begin(), base64_image.end());
        data.push_back('\0');

        DWORD size = 0;
        BYTE* buffer = NULL;

        if (::CryptStringToBinaryA(data.data(), data.size(), CRYPT_STRING_BASE64, buffer, &size, NULL, NULL)) {
            buffer = new BYTE[size];
            if (::CryptStringToBinaryA(data.data(), data.size(), CRYPT_STRING_BASE64, buffer, &size, NULL, NULL)) {
                IStream* stream = SHCreateMemStream(buffer, size);
                bitmap = Gdiplus::Bitmap::FromStream(stream);
                stream->Release();
            }
            delete[] buffer;
        }

        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        Gdiplus::Graphics graphics(hdc);
        graphics.DrawImage(bitmap, 0, 0, 500, 500);

        EndPaint(hwnd, &ps);
        break;
    }
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;

    // 初始化 GDI+
    Gdiplus::GdiplusStartupInput gdiplusStartupInput;
    ULONG_PTR gdiplusToken;
    Gdiplus::GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

    // 注册窗口类
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = 0;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = "MyWindowClass";
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

    if (!RegisterClassEx(&wc)) {
        MessageBox(NULL, "窗口注册失败！", "错误", MB_ICONERROR | MB_OK);
        return 0;
    }

    // 创建窗口
    hwnd = CreateWindowEx(WS_EX_CLIENTEDGE, "MyWindowClass", "窗口标题", WS_VISIBLE | WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 500, 500, NULL, NULL, hInstance, NULL);

    if (hwnd == NULL) {
        MessageBox(NULL, "窗口创建失败！", "错误", MB_ICONERROR | MB_OK);
        return 0;
    }

    // 消息循环
    while (GetMessage(&Msg, NULL, 0, 0) > 0) {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }

    // 关闭 GDI+
    Gdiplus::GdiplusShutdown(gdiplusToken);

    return Msg.wParam;
}