简单的比较C语言下交换a,b数值的代码效率

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以下几个语句都能交换a,b的值

1）

a^=b^=a^=b;

2）

temp = a;a = b;b = temp;

3）

a = a^b;b = a^b;a = a^b;

效率为2） > 3） > 1）

验证代码如下：（linux下GCC和win下codeblocks通过编译）

#include <stdio.h>#include <sys/time.h>#include <unistd.h>void speed_1(){long i = 100000000;while(i){int a = 10;int b = 20;a^=b^=a^=b; i--;}}void speed_2(){long i = 100000000;int temp = 0;while(i){int a = 10;int b = 20;temp = a;a = b;b =  temp;i--;}}void speed_3(){long i = 100000000;while(i) {int a = 10;int b = 20;a = a^b;b = a^b;a = a^b;i--;}}int main(void){struct timeval start;struct timeval end;unsigned long diff_1;             //此处的1，2，3数字代表的代码与上面所列一致unsigned long diff_2;unsigned long diff_3;   gettimeofday(&start, NULL);       //gettimeofday()是C语言获得精确时间函数speed_1();gettimeofday(&end, NULL);diff_1 = 1000000 * (end.tv_sec - start.tv_sec) + end.tv_usec - start.tv_usec;gettimeofday(&start, NULL);speed_2();gettimeofday(&end, NULL);diff_2 = 1000000 * (end.tv_sec - start.tv_sec) + end.tv_usec - start.tv_usec;gettimeofday(&start, NULL);speed_3();gettimeofday(&end, NULL);diff_3 = 1000000 * (end.tv_sec - start.tv_sec) + end.tv_usec - start.tv_usec;printf("time_1 = %ld\n", diff_1);printf("time_2 = %ld\n", diff_2);printf("time_3 = %ld\n", diff_3);return 0;}

记得以前有人深入的分析过，我也不会，就简单的控制变量看下表面现象，看谁的效率更高些。

等以后在尝试从代码角度进行分析吧。