c++ winapi code blocks works and visual studio community not

Question

In code blocks, it works without any errors. But in Visual Studio, it says:

C++ argument of type is incompatible with parameter of type LPCWSTR

This is my code:

#if defined(UNICODE) && !defined(_UNICODE)
    #define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
    #define UNICODE
#endif
#include <windows.h>
    
    
int WINAPI WinMain(HINSTANCE hInst,HINSTANCE hPrev,LPSTR lpCmdLine, int iCmdShow){
    
    int s =  MessageBox(NULL,"Hi This is my First c++ GUI","Win32 API Say:",6);
    if(s == 10){
        MessageBox(NULL,"Hi This is my First c++ GUI","Win32 API Say:",6);
    }else if(s == 11){
        MessageBox(NULL,"Yes GO On","Win32 API Say:",MB_ICONINFORMATION);
    }else{
        MessageBox(NULL,"GoodBey !!","Win32 API Say:",MB_OK);
    }
    return 0;
}

Answer 1

You are using the TCHAR version of MessageBox(), which is actually a preprocessor macro that maps to either MessageBoxW() or MessageBoxA() depending on whether UNICODE is defined or not, respectively.

In case of CodeBlocks, it works if UNICODE is not defined, so MessageBox() maps to MessageBoxA(), which expects LPCSTR (const char *) strings as input. You are passing in char-based string literals, so all is good.

In case of Visual Studio, is fails if UNICODE is defined, so MessageBox() maps to MessageBoxW(), which expects LPCWSTR (const wchar_t *) strings as input. Since you are passing in char-based string literals, and char* is not implicitly convertible to wchar_t*, hence the error.

If you are going to continue using TCHAR functionality ¹, you should wrap your string literals in the TEXT() preprocessor macro to make them use the same character encoding that MessageBox() (or any other TCHAR based API) expects, based on compiler settings.

^{1: you really should not rely on TCHAR in modern code. It exists only for backwards compatibility with legacy code that predates Microsoft's push to get Win9x/ME apps migrated to Unicode on NT4+/Win2K/XP. TCHAR was invented to help such code migrate from ANSI char strings to Unicode wchar_t strings.}

Also, you should not be relying on "magic numbers", either. It makes the code harder to read and understand. Use pre-defined named constants instead. You are already doing that for MB_ICONINFORMATION and MB_OK in your 3rd and 4th calls to MessageBox(), but you are using numeric literals instead for the 1st and 2nd calls to MessageBox().

Try this instead:

#if defined(UNICODE) && !defined(_UNICODE)
    #define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
    #define UNICODE
#endif
#include <windows.h>
    
    
int WINAPI WinMain(HINSTANCE hInst,HINSTANCE hPrev,LPSTR lpCmdLine, int iCmdShow){
    
    int s =  MessageBox(NULL, TEXT("Hi This is my First c++ GUI"), TEXT("Win32 API Say:"), MB_CANCELTRYCONTINUE);
    if(s == IDTRYAGAIN){
        MessageBox(NULL, TEXT("Hi This is my First c++ GUI"), TEXT("Win32 API Say:"), MB_CANCELTRYCONTINUE);
    }else if(s == IDCONTINUE){
        MessageBox(NULL, TEXT("Yes GO On"), TEXT("Win32 API Say:"), MB_ICONINFORMATION);
    }else{
        MessageBox(NULL, TEXT("GoodBey !!"), TEXT("Win32 API Say:"), MB_OK);
    }
    return 0;
}

That said, you should not rely on TCHAR APIs at all, and instead just call MessageBoxA() or MessageBoxW() (or other narrow/wide APIs) directly as needed, eg:

#if defined(UNICODE) && !defined(_UNICODE)
    #define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
    #define UNICODE
#endif
#include <windows.h>
    
    
int WINAPI WinMain(HINSTANCE hInst,HINSTANCE hPrev,LPSTR lpCmdLine, int iCmdShow){
    
    int s =  MessageBoxA(NULL, "Hi This is my First c++ GUI", "Win32 API Say:", MB_CANCELTRYCONTINUE);
    if(s == IDTRYAGAIN){
        MessageBoxA(NULL, "Hi This is my First c++ GUI", "Win32 API Say:", MB_CANCELTRYCONTINUE);
    }else if(s == IDCONTINUE){
        MessageBoxA(NULL, "Yes GO On", "Win32 API Say:", MB_ICONINFORMATION);
    }else{
        MessageBoxA(NULL, "GoodBey !!", "Win32 API Say:", MB_OK);
    }
    return 0;
}

#if defined(UNICODE) && !defined(_UNICODE)
    #define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
    #define UNICODE
#endif
#include <windows.h>
    
    
int WINAPI WinMain(HINSTANCE hInst,HINSTANCE hPrev,LPSTR lpCmdLine, int iCmdShow){
    
    int s =  MessageBoxW(NULL, L"Hi This is my First c++ GUI", L"Win32 API Say:", MB_CANCELTRYCONTINUE);
    if(s == IDTRYAGAIN){
        MessageBoxW(NULL, L"Hi This is my First c++ GUI", L"Win32 API Say:", MB_CANCELTRYCONTINUE);
    }else if(s == IDCONTINUE){
        MessageBoxW(NULL, L"Yes GO On", L"Win32 API Say:", MB_ICONINFORMATION);
    }else{
        MessageBoxW(NULL, L"GoodBey !!", L"Win32 API Say:", MB_OK);
    }
    return 0;
}