这是什么MSVC++编译错误意味着

Question

我有这个编译错误，我不明白什么是错的。我的Microsoft Visual Studio项目是一个Win32项目（非控制台）：

1>MSVCRT.lib(crtexew.obj) : error LNK2001: unresolved external symbol _WinMain@16 
1>C:\Users\Soribo\Desktop\C++ Programming\Visual C++ Programming\KeyboardHook\Release\KeyboardHook.exe : fatal error LNK1120: 1 unresolved externals 

编辑：制作的#include “stdafx.h中” 作为1号线之后的编译错误是：

1>MSVCRT.lib(crtexew.obj) : error LNK2001: unresolved external symbol _WinMain@16 
1>C:\Users\Soribo\Desktop\C++ Programming\Visual C++ Programming\KeyboardHook\Release\KeyboardHook.exe : fatal error LNK1120: 1 unresolved externals 

编辑：嗯，我已经定义WinMain函数有没有我？见下面的代码：

/* 
    Application: 
*/ 

#include <windows.h> 
#include <cstdlib> 
#include "stdafx.h" 

using namespace std; 

static HHOOK  keyboardHook; 
static HINSTANCE gInstance; 


// Functions List // 
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam); 
LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam); 
HHook ActivateKeyboardHook(HookProc hookProc, HINSTANCE hInstance); 
bool DeactivateKeyboardHook(HHook keyboardHook); 


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

    //Step 1: Registering the Window Class 
    wc.cbSize  = sizeof(WNDCLASSEX); 
    wc.style   = 0; 
    wc.lpfnWndProc = WndProc; 
    wc.cbClsExtra = 0; 
    wc.cbWndExtra = 0; 
    wc.hInstance  = gInstance; 
    wc.hIcon   = LoadIcon(NULL, IDI_APPLICATION); 
    wc.hCursor  = LoadCursor(NULL, IDC_ARROW); 
    wc.hbrBackground = (HBRUSH)(DKGRAY_BRUSH); 
    wc.lpszMenuName = NULL; 
    wc.lpszClassName = L"Custom Class"; 
    wc.hIconSm  = LoadIcon(NULL, IDI_APPLICATION); 

    // if registration of main class fails 
    if(!RegisterClassEx(&wc)) 
    { 
     MessageBox(NULL, L"Window Registration Failed!", L"Error!", 
      MB_ICONEXCLAMATION | MB_OK); 
     return 0; 
    } 

    // Step 2: Creating the Window 
    hwnd = CreateWindowEx(
     WS_EX_CLIENTEDGE, 
     L"Custom Class", 
     L"App Name", 
     WS_CAPTION|WS_MINIMIZEBOX|WS_VISIBLE|WS_OVERLAPPED|WS_SYSMENU, 
     CW_USEDEFAULT, CW_USEDEFAULT, 600, 500, 
     NULL, NULL, gInstance, NULL); 

    if(hwnd == NULL) 
    { 
     MessageBox(NULL, L"Window Creation Failed!", L"Error!", 
      MB_ICONEXCLAMATION | MB_OK); 
     return 0; 
    } 

    ShowWindow(hwnd, nCmdShow); 
    UpdateWindow(hwnd); 

    // Step 3: The Message Loop 
    while(GetMessage(&Msg, NULL, 0, 0) > 0) 
    { 
     TranslateMessage(&Msg); 
     DispatchMessage(&Msg); 
    } 
    return Msg.wParam; 
} 

LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam) 
{ 
    /*if (code < 0) 
    { 
     return CallNextHookEx(NULL, code, wParam, lParam); 
    }*/ 

    switch (wParam) 
    { 
     case WM_KEYDOWN: 
     { 
      MessageBox(NULL, L"Notify", L"Key Down", MB_OK);   
     } 
     break; 
     case WM_KEYUP: 
     { 
      MessageBox(NULL, L"Notify", L"Key Up", MB_OK);       
     } 
     break; 
     case WM_SYSKEYDOWN: 
     { 
      MessageBox(NULL, L"Notify", L"Sys Key Down", MB_OK);       
     } 
     break; 
     case WM_SYSKEYUP: 
     { 
      MessageBox(NULL, L"Notify", L"Sys Key Up", MB_OK);       
     } 
     break; 
     default: 
     { 
     } 
     break; 
    } 

    return CallNextHookEx(NULL, nCode, wParam, lParam); 
} 

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) 
{ 

    switch(msg) 
    { 
     case WM_CREATE: 
     {     
      keyboardHook = ActivateKeyboardHook(&LowLevelKeyboardProc, gInstance); 
     }  
     break; 
     case WM_COMMAND: 
     { 
      switch(LOWORD(wParam)) 
      { 

        default: 
        break; 
      } 
     } 
     break; 
     case WM_CLOSE: 
     { 
      DeactivateKeyboardHook(keyboardHook); 
      DestroyWindow(hwnd); 
     } 
     break; 
     case WM_DESTROY: 
      PostQuitMessage(0); 
     break; 
     default: 
     break; 
    } 

    return DefWindowProc(hwnd, msg, wParam, lParam); 
} 

HHOOK ActivateKeyboardHook(HookProc hookProc, HINSTANCE hInstance) 
{ 
    return SetWindowsHookEx(WH_KEYBOARD_LL, hookProc, hInstance, 0); 
} 

bool DeactivateKeyboardHook(HHook keyboardHook) 
{ 
    return UnhookWindowsHookEx(keyboardHook); 
} 

Answer 1

这不是编译错误，即链接器错误，这意味着你的程序没有定义WinMain函数，它是程序的入口点。

确保程序具有这样的功能：

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow); 

看到这个MSDN文档：

• WinMain: The Application Entry Point

---

#include <windows.h> 
#include <cstdlib> 
#include "stdafx.h" 

如果您已经CHOS en预编译的头文件，那么上面是错误的，stdafx.h应该包含在文件的开头。因此，更改顺序为：

#include "stdafx.h" //this should be first line of the program! 
#include <windows.h> 
#include <cstdlib> 

而且我觉得你并不需要包括<windows.h>作为最有可能stdafx.h已经包含它。一探究竟。

现在为什么要先包含它？由于预编译头，顾名思义，是一个预编译头。编译器不会每次都编译它。相反，它会编译一次所有的内容。如果您没有首先包含它，编译器将不知道是否编译之前包含的文件，因为这些文件可能已包含在stdafx.h中，因此已经编译。请参见本主题：

• include stdafx.h in header or source file?（在计算器）
• Use Precompiled Header File（在MSDN）

Answer 2

这不是一个编译错误，它是一个链接错误。基本上，您使用的是某个地方声明的函数，但从未在任何翻译单元中定义。