About rand() & srand() function

TrishaTie

随机产生数字的话，有rand()函数， 但是我也看到了srand()函数， 但是没有很明白srand()的用法，有大神明白的话，求赐教~
这是看到的一个博主的博客： http://blog.chinaunix.net/uid-22623378-id-16480.html
这个是rand() 的自认为比较详细的用法：http://perlmeme.org/howtos/perlfunc/rand_function.html

q1208c

srand 好象是 带种子的吧. 貌似用相同的种子, 可以生成相同的序列

Monox

q1208c 发表于 2014-03-27 11:32
srand 好象是 带种子的吧. 貌似用相同的种子, 可以生成相同的序列

不，srand是用来设置种子的，不是“带”种子的。
一般情况下直接用rand就可以了，不用管srand。再有些特殊需求的时候可能会在调用rand之前先调用srand，比如二楼说的想生成相同的序列，或者出于安全考虑，想设一个复杂点的seed。

jason680

回复 1# TrishaTie

you will get the same serial random number to run your code for each times if you didn't call srand()
Note: Perl will call the srand() by automatic, but you need call the srand() by yourself in awk

$ perl -le 'print rand().",".rand()' | awk '{print "perl rand="$0"\nawk  rand="rand()","rand()}'
perl rand=0.44752758725463,0.832324767575727
awk  rand=0.237788,0.291066

$ perl -le 'print rand().",".rand()' | awk '{print "perl rand="$0"\nawk  rand="rand()","rand()}'
perl rand=0.504112446754338,0.274402088808955
awk  rand=0.237788,0.291066

$ perl -le 'print rand().",".rand()' | awk '{srand();print "perl rand="$0"\nawk  rand="rand()","rand()}'
perl rand=0.494342387261899,0.90917811901042
awk  rand=0.744674,0.889506

$ perl -le 'print rand().",".rand()' | awk '{srand();print "perl rand="$0"\nawk  rand="rand()","rand()}'
perl rand=0.276083956546248,0.33885375070119
awk  rand=0.0146326,0.581655   

q1208c

回复 3# Monox


      果然记错了. 多谢指导.

pitonas

1. Note: Perl will call the srand() by automatic

复制代码

{:2_172:} 感激

jason680 发表于 2014-03-27 06:30
回复 1# TrishaTie

you will get the same serial random number to run your code for each times[/ba ...

TrishaTie

回复 3# Monox
谢谢大神~

TrishaTie

回复 4# jason680

非常感谢大大神赐教~