DECLARE_HANDLE 宏，#,## 预处理指令

在WINNT.H中有这样一段代码:

#define DECLARE_HANDLE(name) struct name##__ { int unused; }; typedef struct name##__ *name

#define sabc(val) #val

#define glue(a,b) a##b



#define MY_DECLARE_HANDLE(name) struct name##__ { int unused; }; typedef struct name##__ *name



struct HTYPE2__ {int unused;}; typedef struct HTYPE2__ * HTYPE2;



MY_DECLARE_HANDLE(HTYPE);

void CTestGetModuleHandleDlg::OnBtnSendmsg() 

{	

	//MessageBox(sabc(中国));			//相当于 MessageBox("中国");

	/*

	int c=20,ab=0;

	glue(a,b) = ++c;	//相当于 ab = ++c;

	CString str;

	str.Format("%d",ab);

	MessageBox(str);

	*/

	

	HTYPE__ type;

	type.unused = 10;

	HTYPE pType = &type;

	CString str;



	HTYPE2 pT = pType;	//error C2440: 'initializing' : cannot convert from 'struct HTYPE2__ *' to 'struct HTYPE__ *'

	str.Format("%d,%d",type.unused,pType->unused);

	MessageBox(str);

}

 

 

Function macro definitions accept two special operators (# and ##) in the replacement sequence:
If the operator # is used before a parameter is used in the replacement sequence, that parameter is replaced by a string literal (as if it were enclosed between double quotes)

1	#define str(x) #x cout << str(test);

This would be translated into:

cout << "test";

The operator ## concatenates two arguments leaving no blank spaces between them:

1	#define glue(a,b) a ## b glue(c,out) << "test";

This would also be translated into:

cout << "test";

 

现在明白了，之所以定义这个宏去声明 结构体与结构体指针，就是为了让句柄之间转化赋值时能在编绎时检测到不匹配的赋值。

从使用者的角度上看，也非常简练。不得不佩服微软的人，确实是个好点子。