Strange error for member function declaration

Question

Below is something that did happen to me and I couldn't get what's wrong. My coworker and me screwed our heads around this. It was in a cross-platform library using the cross-platform toolkit wxWidgets on Windows

#include <wx/wx.h> 

class Graph {
public:
  // ...
  // main1.cpp:4:10: error: expected identifier before '(' token
  double GetYValue(double x);
};

We were trying hard to find any weird glyph placed instead of an ASCII e or something, but didn't find any such issue. What was going on!?

Answer 1

WinGDI.h ln 640: #define GetYValue(cmyk) ((BYTE)((cmyk)>> 8))

Gotta love windows.h

This is why I recommend AGAINST using camel case for most things.

Answer 2

I don't use wxWidgets myself, but in http://gambit.sourcearchive.com/documentation/0.2006.01.20/plotctrl_8cpp-source.html I find strange code fragment

#ifdef GetYValue   // Visual Studio 7 defines this
    #undef GetYValue
#endif

Look at the wxWidgets headers. Probably are there a code fragment like this or you should do something like this?

Answer 3

My first guess would be that <wx/wx.h> has a macro named GetYValue (and probably another named GetXValue) that are supposed to take some sort of combined X/Y value and "unwrap" them into their individual components, on the general order of:

#define GetXValue(xy) ((xy)>>16)
#define GetYValue(xy) ((xy)&x0ff)

With that expanded, your code would look something like:

double ((xy)>>16)(double x);

...at which point the compiler has a hissy fit -- except, of course, that it probably gave up parsing sooner than that, since the double x appears to be trying pass two tokens as parameters to a macro that only expects 1.

Edit: I see I was guessing fairly close, but guessed wrong about what sort of "Y" was involved here -- the others would apparently be GetCValue, GetMValue, etc., instead of GetXValue. Oh well...