C语言预处理详解

__FILE__      //进行编译的源文件
__LINE__     //文件当前的行号
__DATE__    //文件被编译的日期
__TIME__    //文件被编译的时间
__STDC__    //如果编译器遵循ANSI C，其值为1，否则未定义

 int main()
{
	printf("%s\n", __FILE__);
	printf("%d\n", __LINE__);
	printf("%s\n", __DATE__);
	printf("%s\n", __TIME__);
	//printf("%d\n", __STDC__);//因为VS不支持ANSI C,其实__STDC__未定义
	//GCc 是支持的
	//gcc对C语言语法的支持非常好
 	return 0;
}

 int main()
 {
	 printf("file:%s line:%d\n", __FILE__, __LINE__);
	 return 0;
 }

#define name stuff

#define MAX 100
#define reg reGISter    //为 register这个关键字，创建一个简短的名字
#define STR "HEHE"
int main()
{
	int a = 3;
	int b = 20;
	if (a == 4)
		b = MAX;
	else
		b = -a;
	register int num = 100;
	reg int num2 = 200;
 	int m = MAX;
	printf("%d\n", MAX);
	printf("%d\n", m);
	printf("%s\n", STR);
 	return 0;
}

#define MAX 1000;
int main()
{
	int x = 1;
	int max;
	if (x==1)
	{
		max = MAX;//这里替换为 MAX 1000;;语法错误
	}
	else
	{
		max = 0;
	}
	printf("%d", max);
	return 0;
}

#define SQUARE( x ) x * x

SQUARE( 5 );

5 * 5

int a = 5;
printf("%d\n" ,SQUARE( a + 1) );

#define SQUARE(x) (x) * (x)

printf ("%d\n",(a + 1) * (a + 1) );

#define SQUARE(X) ((X)*(X))
 int main()
{
	int a = 5;
	int ret = SQUARE(a+5);
	//int ret = a + 5 * a + 5;
	//int ret = ((a) * (a));
	printf("%d\n", ret);
 	return 0;
}

#define DOUBLE(x) (x) + (x)

int a = 5; 
printf("%d\n" ,10 * DOUBLE(a)); 

printf ("%d\n",10 * (5) + (5));

#define DOUBLE(x) ( ( x ) + ( x ) )

#define DOUBLE(X) ((X)+(X))
 int main()
{
	int ret = 10 * DOUBLE(2);
	//int ret = 10 * 2 + 2;
 	printf("%d\n", ret);
 	return 0;
}

#define PRINT(n) printf("the value of "#n" is %d\n", n)
 int main()
{
	int a = 10;
	PRINT(a);
	int b = 20;
	PRINT(b);
	return 0;
}

#define PRINT(FORMAT, VALUE)
printf("the value is "FORMAT"\n", VALUE);
PRINT("%d", 10);

#define PRINT(n) printf("the value of "#n" is %d\n", n)
 int main()
{
	int a = 10;
	printf("the value of a is %d\n", a);
	int b = 20;
	printf("the value of b is %d\n", b);
	printf("hello world\n");
	printf("hello ""world\n");
	return 0;
}

#define ADD_TO_SUM(num, value) 
sum##num += value; 
 ADD_TO_SUM(5, 10);//作用是：给sum5增加10.

#define CAT(X,Y) X##Y
 int main()
{
	int class103 = 100;
	printf("%d\n", CAT(class, 103));
	printf("%d\n", CAT(1, 2));
	return 0;
}

x+1;//不带副作用
x++;//带有副作用

int main()
{
	int a = 10;
	int b = a + 1;//b得到的是11，a不变
	int b = ++a;//b得到的是11，但是a变了，这个表达式是有副作用的
	return 0;
}

int Max(int x, int y)
{
	return x > y ? x : y;
}
 int main()
{
	int a = 5;
	int b = 8;
 	//int m = MAX(a++, b++);
	//int m = ((a++) > (b++) ? (a++) : (b++));
	//函数的参数是计算后再传进去的
	int m = Max(a++, b++);
 	printf("m=%d\n", m);//8
	printf("a=%d\n", a);//6
	printf("b=%d\n", b);//9
  	return 0;
}

//宏的实现 - 1
#define MAX(X,Y) ((X)>(Y)?(X):(Y))
int Max(int x, int y)
{
	return x > y ? x : y;
}
 int main()
{
	int a = 5;
	int b = 8;
	//宏的参数是不计算直接替换进去的
	//替换进去进去后参与运算
 	int m = Max(a++, b++);
 	printf("m=%d\n", m);//8
	printf("a=%d\n", a);//6
	printf("b=%d\n", b);//9
 	return 0;

#define MAX(a, b) ((a)>(b)?(a):(b)) 

#undef NAME 
//如果现存的一个名字需要被重新定义，那么它的旧名字首先要被移除。

#define	MAX 100
 int main()
{
	int m = MAX;
    #undef MAX
	int n = MAX;//err
	return 0;
}

#define M 500
 int main()
{
#if M==100
	printf("haha\n");
#elif M==200
	printf("hehe\n");
#else
	printf("heihei\n");
#endif
 	return 0;
}

#include "filename" 

C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include

#include <filename.h>