cannot convert cont char* to LPCWSTR

Question

I am stuck with an error in QT compiler however it works fine with VS2010. the error states that I have seen other posts related to the same error but non has resolved my problem in QT. I have tried _T,L or TEXT but still not working

bq. error: C2664: 'HANDLE LoadImageW(HINSTANCE,LPCWSTR,UINT,int,int,UINT)' : cannot convert argument 2 from 'const char *' to 'LPCWSTR' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

my code is as below

Bitmap::Bitmap(std::string const& file_name) {
bitmap_ = static_cast<HBITMAP>(::LoadImage(0, file_name.c_str(), IMAGE_BITMAP,0,0,LR_LOADFROMFILE|LR_CREATEDIBSECTION));
}

please share if you have any idea to resolve this

Answer 1

Qt does not include a compiler. On Windows you're probably either compiling with mingw or Visual C++. Either way, the issue is that you're calling a function that expects a wide character string but you're trying to hand it an 8-bit character string.

For compatibility reasons, Win32 uses a different set of API functions if you have _UNICODE defined. In your case, you do have _UNICODE defined. You can continue using the 8-bit std::string but simply change the method from LoadImage() to LoadImageA(). Or if you don't mind changing your Bitmap class, you could switch from std::string to std::wstring to take advantage of Windows' Unicode features.

But perhaps the larger question is why use Win32 to load bitmaps and std::string if you're using Qt? Qt's QImage class and QString class provide a full-featured, cross-platform strings and image loaders. Like any comprehensive framework, Qt works best if you only use external features on an as-needed basis.

Answer 2

I'm not sure if this method is the best, but I've used them on my projects and it works fine, see:

char *source = "Hello world";
WCHAR target[size];
MultiByteToWideChar(CP_ACP, 0, source, -1, target, size);
LPCWSTR final = target;

MessageBox(0, final, TEXT("title"), 0); //Sample usage