linux内核中的min(x,y)和max(x,y)宏定义

/linux/include/linux/kernel.h中有min(x, y)和max(x, y)的定义如下

 #define min(x, y) ({ 
      typeof(x) _min1 = x; 
       typeof(y) _min2 = y; 
       (void) (&_min1 == &_min2); 
       _min1 < _min2 ? _min1 ： _min2; })
   
    #define max(x, y) ({ 
      typeof(x) _max1 = x; 
       typeof(y) _max2 = y; 
      (void) (&_max1 == &_max2); 
      _max1 > _max2 ? _max1 : _max2; }

 (void) (&_max1 == &_max2); 的作用为：防止不同类型的参数进行比较；

http://www.mybbchina.net/linuxneihe/128535.html

instance analysis1:

#include <stdio.h>

#define min(x,y)  ({          \
        const typeof(x) _x = (x); \
        const typeof(y) _y = (y); \
        (void) (&_x == &_y)      ; \
        _x < _y ? _x : _y      ; })

//#define min(x, y) ({ \
//       typeof(x) _min1 = x; \
//       typeof(y) _min2 = y; \
//       (void) (&_min1 == &_min2); \
//       _min1 < _min2 ? _min1 : _min2; })

int main()
{
    int  mini;
    float  minf;

    mini = min( 3, 2);
    minf = min( 3, 2);
    printf("mini:%d minf:%f \n", mini, minf);

    return 0;
}

instance analysis2: 

#include <stdio.h>

#define MIN_T(type, x, y) \
        ({ type _x = (x); type _y = (y); _x < _y ? _x:_y ;})

int main()
{
    int ia = 1, ib =2, mini;
    float fa = 3, fb=2, minf;

    mini = MIN_T(int , ia, ib);
    minf = MIN_T(float, fa, fb);

    printf("mini:%d minf:%f\n", mini, minf);

    return 0;
}

instance analysis3:

 

#include <stdio.h>

#define min(x,y) ((x) < (y) ? (x) : (y))

#define MIN_T1(x,y)  ({          \
        const typeof(x) _x = (x); \
        const typeof(y) _y = (y); \
        (void) (&_x == &_y)      ; \
        _x < _y ? _x : _y      ; })

#define MIN_T2(type, x, y) \
        ({ type _x = (x); type _y = (y); _x < _y ? _x:_y ;})

int main()
{
    int ia = 1,ja = 1;
    int ib = 2,jb = 2;
    int mini = -1;

    mini = min(++ia, ++ib);
    printf("mini:%d %d %d \n", mini,ia, ib);

    int minj = MIN_T1(++ja, ++jb);
    printf("mini:%d %d %d\n", minj, ja, jb);

    return 0;
}

由此看出内核更安全，可靠性更高！有空多看内核