Question

I have this compile error that I dont understand what is wrong. My Microsoft Visual Studio project is a Win32 Project (not console):

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

EDIT: After making #include “stdafx.h” as the 1st line the compile error is:

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

EDIT: hmm, I have defined WinMain function haven’t I? see below code:

/*
  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

That is not compilation error, that is linker error, and it means your program doesn’t define WinMain function, which is entry point of the program.

Make sure your program has this function:

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

See this MSDN documentation:

• WinMain: The Application Entry Point

---

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

If you’ve chosen precompiled header file, then the above is wrong, stdafx.h should be included at the beginning of the file. So change the order as:

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

And I think you don’t need to include <windows.h> as most likely stdafx.h have included it already. Check it out.

Now why should it be included first? Because precompiled header, as the name suggests, is a precompiled header. The compiler doesn’t compile it everytime. Instead, it compiles all the content in it once. If you don’t include it first, the compiler will not know that whether to compile the files included before it or not, because it may be that those files are already included in stdafx.h and so has already be compiled. See this topic:

• include stdafx.h in header or source file? (at stackoverflow)
• Use Precompiled Header File (at MSDN)