Pointers and references (convert char to LPCWSTR)

Question

Here I'm resolving an error which occurs in VS2013, while working with Glut-library. As I see - it is a simple problem with pointers and references. So, the output for the 11th line is:

## error C2664: 'AUX_RGBImageRec *auxDIBImageLoadW(LPCWSTR)' : cannot convert argument 1 from 'char [13]' to 'LPCWSTR'

Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

Where is the mistake? It must be a (*) sign missed in the 11th line.

void TextureInit()
{
 char strFile[]="Particle.bmp";
 AUX_RGBImageRec *pImage;
 /* Выравнивание в *.bmp по байту */
 glPixelStorei(GL_UNPACK_ALIGNMENT,1);
 /* Создание идентификатора для текстуры */
 glGenTextures(1,&TexId[0]);
 /* Загрузка изображения в память */

 pImage = auxDIBImageLoad(strFile);

 /* Начало описания свойств текстуры */
 glBindTexture(GL_TEXTURE_2D,TexId[0]);
 /* Создание уровней детализации и инициализация текстуры
  */
 gluBuild2DMipmaps(GL_TEXTURE_2D,GL_RGB,pImage->sizeX,
                   pImage->sizeY,GL_RGB,GL_UNSIGNED_BYTE,
                   pImage->data);

 /* Задание параметров текстуры */
 /* Повтор изображения по параметрическим осям s и t */
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
 /* Не использовать интерполяцию при выборе точки на
 * текстуре
  */
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 /* Совмещать текстуру и материал объекта */
 glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
 glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
}

Answer 1

I assume you do not intend to use the Unicode libraries. In this case, remove the macro definition of _UNICODE and UNICODE in the project properties, and use _MBCS instead. This, however, makes more likely that the characters can go wrong on Windows machines that use a different locale.

Generally speaking, one should not directly use char or wchar_t to interface with the Windows API. For maximum compatibility, you should wrap them in the _T macro. Instead of writing

char strFile[]="Particle.bmp";

write

TCHAR strFile[]=_T("Particle.bmp");

Consult Microsoft documentation for more details.

Answer 2

This isn't a pointer/reference problem, it's a string encoding problem. auxDIBImageLoadW takes anLPCWSTR - a UTF-16 string. You're trying to pass it an ASCII string.

To fix this, declare strFile as wchar_t strFile[] = L"Particle.bmp";.

Answer 3

In Unicode builds (which have been the default since VS2005), auxDIBImageLoad() is expanded to auxDIBImageLoadW() (the ending W stands for Wide characters, i.e wchar_ts), which is the Unicode UTF-16 version of the API.

The strFile argument that you passed to auxDIBImageLoadW() is instead a char-string (not a wchar_t string), defined as:

char strFile[]="Particle.bmp";

So you have a mismatch in the string parameter.

An option is to just define strFile as a wchar_t string (note also the L prefix to define the string literal):

wchar_t strFile[] = L"Particle.bmp";

Or, if for some reason you must have a char string, you can convert it at the call site, using the ATL helper macro CA2W (which converts from Aansi - i.e. char-string - to Wide Unicode UTF-16 wchar_t string):

#include <atlconv.h> // for CA2W

// char strFile[]...
pImage = auxDIBImageLoad(CA2W(strFile));

(The CA2W is a convenient RAII wrapper around the ::MultiByteToWideChar() Win32 API.)

Answer 4

Noone of the methods could resolve. But funally I came to another part, which I've moved to another topic: [https://stackoverflow.com/questions/23064256/opening-a-bmp-with-auxdibimageload-within-glut-library][1]