简化重载的类函数

Question

I am having in my class gTexture two functions declared:

public:
                               gTexture():mActiveTexture(0){...}
   virtual void                DrawTexture();
   virtual void                DrawTexture(unsigned short int TextureNumber);
           int                 mActiveTexture;

where

void gTexture::DrawTexture()
    {
    gTexture::DrawTexture(mActiveTexture);
    }

I'd like to have this in one function something like

virtual void                DrawTexture(unsigned short int TextureNumber=mActiveTexture);

This does no compile as mActiveTexture is an invalid use of non static data member. Is there any way to just have one function, which would make it easier to handle with my derived objects? Thanks.

Answer 1

I can see two ways. Both are workaround-ish, but could be useful.

One is to make the parameterless function non-virtual; it will simply always call the second one with mActiveTexture .

The other way is to use domain knowledge (specifically the fact that 0 is not a valid OpenGL texture name) and do this:

virtual void DrawTexture(unsigned short int TextureNumber = 0) {
  if (TextureNumber == 0) TextureNumber = mActiveTexture;
  // ... rest of the code
}

Answer 2

You could have a default argument value that is not valid (eg -1). Then your function can check if that value is the default and if it is, use mActiveTexture, otherwise it will use the argument.

Answer 3

No, you can't use members as defaults. Defaults are used at compile time.

You could however use a special value for the default, like -1 and then check in DrawTexture if the input values is -1 and if so set it to mActiveTexture.