Deep discussion on the usage of MACRO

see the code directly:

/* macro.c by vinco at 2011-09-15
*   i386-Red Hat-gcc-4.1.2 
*   http://blog.youkuaiyun.com/xuyunzhang/
*   Copyright: All Reserved
*/

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define conn(x,y) 		x##y	//xy,    (x)##(y) is not correct !!!
#define toString(x) 	#x 		//"x",   #(x) is not correct !!!
#define SWAP_INT(x,y)	({(x)^=(y)^=(x)^=(y);}) //can x,y be point !!!

/* support both struct type and basic type, but not point */
#define SWAP_GENERAL(x,y,DATA_TYPE)	do{\
	DATA_TYPE tmp;\
	memcpy(&tmp, &x, sizeof(DATA_TYPE) );\
	memcpy(&x, &y, sizeof(DATA_TYPE) );\
	memcpy(&y, &tmp, sizeof(DATA_TYPE) );\
	}while(0)
	
/* support only point/address !!! */
#define SWAP_POINT(x,y,DATA_TYPE)	do{\
	DATA_TYPE tmp;\
	memcpy(&tmp, x, sizeof(DATA_TYPE) );\
	memcpy(x, y, sizeof(DATA_TYPE) );\
	memcpy(y, &tmp, sizeof(DATA_TYPE) );\
	}while(0)

typedef struct classmate
{
	int age;
	char name[30];
}ClassMate;

void FuncTest(void);

int main(void)
{
	/*-----------------------------------------------*/
	int num= conn(123,456);
	//int num = (123##456);

	char* pStr = toString(vinco zhang);
	//char* p = #vinco;

	printf("num = %d\n", num);
	printf("pStr = %s\n", pStr);

	putchar('\n');
	/*-----------------------------------------------*/
	int x =10,y=20;
	printf("x=%d, y=%d\n", x, y);
	SWAP_INT(x,y);
	//SWAP_GENERAL( x, y, int); // is ok too !!!
	printf("x=%d, y=%d\n", x, y);

	putchar('\n');
	/*-----------------------------------------------*/
	int *px =&x,*py=&y;
	printf("*px=%d, *py=%d\n", *px, *py);

	//SWAP_INT( px, py);     // error of course !!!
	//SWAP_INT( *px, *py); //not correct, but why ???
	
	//SWAP_GENERAL( *px, *py, int); // is ok too !!!
	SWAP_POINT( px, py, int);
	printf("*px=%d, *py=%d\n", *px, *py);
	
	putchar('\n');
	/*-----------------------------------------------*/
	ClassMate classmates[2] =
	{
		{124, "vinco" },
		{24, "zhang" }
	};
	printf("classmates[0].age = %d, classmates[0].name = %s\n", classmates[0].age, classmates[0].name );
	printf("classmates[1].age = %d, classmates[1].name = %s\n", classmates[1].age, classmates[1].name );
	SWAP_GENERAL(classmates[0], classmates[1], ClassMate); 
	//SWAP_POINT(&classmates[0], &classmates[1], ClassMate); //is ok too !!!
	printf("classmates[0].age = %d, classmates[0].name = %s\n", classmates[0].age, classmates[0].name );
	printf("classmates[1].age = %d, classmates[1].name = %s\n", classmates[1].age, classmates[1].name );

	putchar('\n');
	/*-----------------------------------------------*/
	ClassMate* pClassmates[2] =
	{
		&classmates[0],
		&classmates[1]
	};
	printf("pClassmates[0]->age = %d, pClassmates[0]->name = %s\n", pClassmates[0]->age, pClassmates[0]->name );
	printf("pClassmates[1].age = %d, pClassmates[1]->name = %s\n", pClassmates[1]->age, pClassmates[1]->name );
	//SWAP_GENERAL( *pClassmates[0], *pClassmates[1], ClassMate); //is ok too !!!
	SWAP_POINT( pClassmates[0], pClassmates[1], ClassMate);
	printf("pClassmates[0]->age = %d, pClassmates[0]->name = %s\n", pClassmates[0]->age, pClassmates[0]->name );
	printf("pClassmates[1]->age = %d, pClassmates[1]->name = %s\n", pClassmates[1]->age, pClassmates[1]->name );

	putchar('\n');
	/*-----------------------------------------------*/
	FuncTest();
	/*-----------------------------------------------*/
	return 0;
}


void FuncTest(void)
{
	printf( "The %s is %s\n", toString(__FUNCTION__), __FUNCTION__ );
	printf( "The %s is %s\n", toString(__FILE__), __FILE__ );
	printf( "The %s is %d\n", toString(__LINE__), __LINE__ );
	printf( "The %s is %s\n", toString(__DATE__), __DATE__ );
	printf( "The %s is %s\n", toString(__TIME__), __TIME__ );
} 

make and run  it:

[vinco@IPPBX-Server ctest]$ make macro
cc     macro.c   -o macro
[vinco@IPPBX-Server ctest]$ ./macro
num = 123456
pStr = vinco zhang

x=10, y=20
x=20, y=10

*px=20, *py=10
*px=10, *py=20

classmates[0].age = 124, classmates[0].name = vinco
classmates[1].age = 24, classmates[1].name = zhang
classmates[0].age = 24, classmates[0].name = zhang
classmates[1].age = 124, classmates[1].name = vinco

pClassmates[0]->age = 24, pClassmates[0]->name = zhang
pClassmates[1].age = 124, pClassmates[1]->name = vinco
pClassmates[0]->age = 124, pClassmates[0]->name = vinco
pClassmates[1]->age = 24, pClassmates[1]->name = zhang

The __FUNCTION__ is FuncTest
The __FILE__ is macro.c
The __LINE__ is 111
The __DATE__ is Sep 15 2011
The __TIME__ is 17:36:13
[vinco@IPPBX-Server ctest]$ 

 

1. " #define toChar(x)#@x //'x' "
it's not support in gcc, at least in Red Hat-gcc-4.1.2 and Ubuntu-gcc-4.3.2

however, it's supported in Visual C++ 6.0 .

2.
#define conn(x,y)   (x)##(y)  //xy,
#define toString(x)   #(x)   //"x",
are not correct !!!

3. some syntax is only suitable for macro defination, it accur error once used in general place.
int i = (123##456);
char* p = #vinco;
are error !!!

4. the value of a specific macro is determined once complete compiled, otherwise compile it again.
so the value of "__DATE__" and  "__DATE__" are not changed even although execute the programm many times.

5. macro is really a good skill you can take for, especially the macro with parameter.
because it merely do some about substitution, the paremeter can be the type itself,
such as "char", "struct ClassMate".
just see "SWAP_GENERAL(x,y,DATA_TYPE)".

6. GCC support "{ any; specific; context; }" now!!! , it's equivalent to "do{any; specific; context;}while(0)",
any more , you can distribute it to several lines just by adding "\" to the end per line.
(no space charater followed any more, including ' ','\t')