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c++ - 来自 MSVCRTD.lib 的 LNK2019 未解析的外部符号

问题描述

我是 C++ 新手，仍在努力学习它。我有一些从这里复制过来的代码。

问题是我非常仔细地按照说明进行操作，但即使我做的事情很艰难，仍然会出错，这正是他们告诉我要做的，它不起作用。

// HelloWindowsDesktop.cpp
// compile with: /D_UNICODE /DUNICODE /DWIN32 /D_WINDOWS /c

#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <tchar.h>

// Global variables

// The main window class name.
static TCHAR szWindowClass[] = _T("DesktopApp");

// The string that appears in the application's title bar.
static TCHAR szTitle[] = _T("Windows Desktop Guided Tour Application");

HINSTANCE hInst;

// Forward declarations of functions included in this code module:
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int CALLBACK WinMain(
    _In_ HINSTANCE hInstance,
    _In_ HINSTANCE hPrevInstance,
    _In_ LPSTR     lpCmdLine,
    _In_ int       nCmdShow
)
{
    WNDCLASSEX wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc = WndProc;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance;
    wcex.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = szWindowClass;
    wcex.hIconSm = LoadIcon(wcex.hInstance, IDI_APPLICATION);

    if (!RegisterClassEx(&wcex))
    {
        MessageBox(NULL,
            _T("Call to RegisterClassEx failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    }

    // Store instance handle in our global variable
    hInst = hInstance;

    // The parameters to CreateWindow explained:
    // szWindowClass: the name of the application
    // szTitle: the text that appears in the title bar
    // WS_OVERLAPPEDWINDOW: the type of window to create
    // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
    // 500, 100: initial size (width, length)
    // NULL: the parent of this window
    // NULL: this application does not have a menu bar
    // hInstance: the first parameter from WinMain
    // NULL: not used in this application
    HWND hWnd = CreateWindow(
        szWindowClass,
        szTitle,
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        500, 100,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if (!hWnd)
    {
        MessageBox(NULL,
            _T("Call to CreateWindow failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    }

    // The parameters to ShowWindow explained:
    // hWnd: the value returned from CreateWindow
    // nCmdShow: the fourth parameter from WinMain
    ShowWindow(hWnd,
        nCmdShow);
    UpdateWindow(hWnd);

    // Main message loop:
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}

//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    HDC hdc;
    TCHAR greeting[] = _T("Hello, Windows desktop!");

    switch (message)
    {
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);

        // Here your application is laid out.
        // For this introduction, we just print out "Hello, Windows desktop!"
        // in the top left corner.
        TextOut(hdc,
            5, 5,
            greeting, _tcslen(greeting));
        // End application-specific layout section.

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

    return 0;
}

这些是错误：

第一个错误：

错误 LNK2019 未解析的外部符号 _main 在函数“int >__cdecl invoke_main(void)”(?invoke_main@@YAHXZ) Learn1 >C:\Users\user\source\repos\Learn1\Learn1\MSVCRTD.lib(exe_main.obj) 中引用1

第二个错误：

错误 LNK1120 1 无法解析的外部 Learn1 >C:\Users\user\source\repos\Learn1\Debug\Learn1.exe 1

我怀疑第二个错误出现在第一个错误之后。因此，如果第一个解决了，第二个也将解决。

标签： c++windowsvisual-c++

解决方案

/SUBSYSTEM:CONSOLE) 用于基于控制台的应用程序。您应该main在代码中定义函数。

/SUBSYSTEM:WINDOWS) 用于 GUI 应用程序。你应该定义 WinMain功能

您已选择子系统作为 CONSOLE，并且应该是 WINDOWS，因为您有 WinMain 和消息处理程序。

您可以在项目属性下更改它

Project>Properties>Linker>System>Subsystem

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