XGetWindowAttributes and You

Right at the end of a project I've been working on, I run into a very weird issue. As per the title of this post, it's with XGetWindowAttributes and the XWindowAttributes struct.

Reference page:
XGetWindowAttributes

The main reason I'm looking to use this function is for XWindowAttributes.class, which will tell me if the window I have is InputOutput (visible) or InputOnly (not visible). If there's a simpler way to detect a window's visibility, I couldn't find it.

Anyway, in my coding I have this:

    XWindowAttributes attr;
    XGetWindowAttributes(display, hwnd, &attr);
    if(attr.class == InputOutput){
        [...]
    }else{
        [...]
    }

Looks fine, yes? Well, it won't compile.

error: expected unqualified-id before class
error: expected `)' before class

Some research on the error turns up next to nothing; just a bunch of people saying that switching header include orders fixes it. Didn't fix it for me.

So then I figure, perhaps the documentation is old, and "class" has been removed. Changing "class" to a random string returns a different error, so that's not it. So I looked at the newest documentation I could find - the source. Turns out that it WAS changed, and here it is (abbridged):

typedef struct {
    int x, y;                   /* location of window */
    [...]
    Window root;                /* root of screen containing window */
#if defined(__cplusplus) || defined(c_plusplus)
    int c_class;                /* C++ InputOutput, InputOnly*/
#else
    int class;                  /* InputOutput, InputOnly*/
#endif
    int bit_gravity;            /* one of bit gravity values */
    [...]
    Screen *screen;             /* back pointer to correct screen */
} XWindowAttributes;

As it turns out, my code is C++, and apparently there's a different member for C and C++ (whoever heard of doing that? I fail to see the reasoning - though I'm sure there is some).

Anyway, a simple change of variable name to c_class fixed the errors, and it compiles successfully. Mark another one up for non-deterministic error messages.