预处理、宏定义

 

#include <stdio.h>

#define MAX(x,y) (x>y?x:y)
#define PRINT_INT(x) printf(#x" %d\n",x)
#define PRINT_F(x) printf(#x" %f\n",x)

#define PRINT_HELLO() \
    printf("Hello, World\n")

#define GENERIC_MAX(type)  \
    type type##_max(type x,type y) \
    {                              \
       return x>y?x:y;             \
    }                              \

#define CHECK_ZERO(divisor) \
    if (divisor == 0) \
    printf("*** Attempt to divide by zero on line %d "\
            "of file %s ***\n",__LINE__,__FILE__)

int main()
{
  printf("Wacky Windows (c) 1996 Wacky Software, Inc.\n");
  printf("Compiled on %s at %s\n", __DATE__,__TIME__);

  printf("Hello \n");
#ifdef DEBUG
  printf("Debug...\n");
#endif

  printf("max: %d\n",MAX(3,4));
  int x = 1021;
  PRINT_INT(x);
  PRINT_HELLO();
  GENERIC_MAX(int);
  int z = int_max(5,1);
  GENERIC_MAX(float);
  float f = float_max(12.3,11.1);
  PRINT_INT(z);
  PRINT_F(f);
  int i = 100, j = 1;
  CHECK_ZERO(j);
  int k = i/j;

}

gcc -DDEBUG t.c
./a.out
Wacky Windows (c) 1996 Wacky Software, Inc.
Compiled on Nov 30 2012 at 11:57:49
Hello
Debug...
max: 4
x 1021
Hello, World
z 5
f 12.300000

 

注：

宏参数没有类型检查；

无法用一个指针来指向宏；

宏可能会不止一次地计算它的参数，如： MAX(i++,j);

在涉及到运算操作时记得要添加圆括号

#define error_check(rc,str)                                            \
        if(rc < 0) {                                                   \
            fprintf(stderr,"%s: In function '%s' line(%d): %s, %s.\n", \
            __FILE__, __FUNCTION__,__LINE__,str,strerror(errno));      \
            exit(1);                                                   \
        }

#define set_nonblock(fd)                                                 \
        {int rc = fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);   \
         error_check(rc,"fcntl: set_nonblock");}