答案是yes
srand改变了全局变量,所以在任何地方调用一次都会影响后续的rand返回值
C标准给了一个sample implementation,如下(http://stackoverflow.com/questions/4768180/rand-implementation,
main函数能被调用吗、http://stackoverflow.com/questions/7343833/srand-why-call-only-once)
static unsigned long int next = 1;int rand(void) // RAND_MAX assumed to be 32767 {next = next * 1103515245 + 12345;return (unsigned int)(next/65536) % 32768; }void srand(unsigned int seed) {next = seed; }
由这个代码应该可以比较清楚地看到:next是个全局变量,每次调用srand都会修改next,而每次调用rand都要首先读取这个值,并且修改这个值。也就是说,srand对next的修改——对rand来说——是可见的
一个小测试:
#include <stdio.h> #include <stdlib.h>void print_rand() {for (int i = 0; i < 5; i++) {printf("%d,", rand());}printf("\n"); }int main(int argc, const char *argv[]) {srand(123);for (int i = 0; i < 5; i++) {printf("%d,", rand());}srand(123);//观察注释后的结果,对比 print_rand();return 0; }
注释前结果:440,19053,23075,13104,32363,440,19053,23075,13104,32363,
c语言如何调用函数、注释后结果:440,19053,23075,13104,32363,3265,30749,32678,9760,28064,
测试也验证了我们的推断