What is the meaning of this C++ macro? -

i can't figure out macro means:

#define declare_handle(n) typedef struct n##__{int i;}*n  declare_handle(hwnd); 

i have learned c program that:

"##" means connect parameter.

so macro equals:

typedef struct hwnd__{int i;}*hwnd 

is right?

if right, meaning of sentence?

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code game bombermaaan (for windows , linux),
link http://sourceforge.net/p/bombermaaan/code/head/tree/trunk/src/bombermaaan/winreplace.h,
line no 90.

the main purpose of construct prevent misuse of handles. if handles void * or int or long long or other basic type, there nothing prevent using 1 instead of another. pointer struct hwnd__ , pointer struct hbitmap__ isn't same thing, if have following code:

hwnd hwnd; hbitmap hbmp;  hbmp = getbitmap(...); hwnd = hbmp;    // gives compiler error.  

it's classic technique ensure unique types api supplier don't want provide true declaration for. although i'm not entirely sure why need proper struct declaration, away with:

#define declare_handle(n) struct n ## __; struct n ## __ *n; 

that ensure dereferece hwnd won't possible, since compiler object "use of incomplete type".