srand(time(0));是什么意思呀

[g_yxh]

在银行柜台与客户的算法里有这么一句,是什么意思?

[born20c]

rcmcs@ctihf:/ora2/rcmcs/tmp > man srand
重新格式化页 请等待... 完成

C Library Functions rand(3C)

NAME
rand, srand, rand_r - simple random-number generator

SYNOPSIS
#include <stdlib.h>

int rand(void);

void srand(unsigned int seed);

int rand_r(unsigned int *seed);

DESCRIPTION
The rand() function uses a multiplicative congruential
random-number generator with period 2**32 that returns suc-
cessive pseudo-random numbers in the range of 0 to RAND_MAX
(defined in <stdlib.h>).

The srand() function uses the argument seed as a seed for a
new sequence of pseudo-random numbers to be returned by sub-
sequent calls to rand(). If srand() is then called with the
same seed value, the sequence of pseudo-random numbers will
be repeated. If rand() is called before any calls to
srand() have been made, the same sequence will be generated
as when srand() is first called with a seed value of 1.

The rand_r() function has the same functionality as rand()
except that a pointer to a seed seed must be supplied by
the caller. The seed to be supplied is not the same seed as
in srand().

USAGE
The spectral....

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rcmcs@ctihf:/ora2/rcmcs/tmp > man time
重新格式化页 请等待... 完成

User Commands time(1)

NAME
time - time a simple command

SYNOPSIS
time [ -p ] utility [ argument. .. ]

DESCRIPTION
The time utility invokes utility operand with argument, and
writes a message to standard error that lists timing statis-
tics for utility. The message includes the following infor-
mation:

o The elapsed (real) time between invocation of utility
and its termination.

o The User CPU time, equivalent to the sum of the
tms_utime and tms_cutime fields returned by the
times(2) function for the process in which utility is
executed.

o The System CPU time, equivalent to the sum of the
tms_stime and tms_cstime fields returned by the
times() function for the process in which utility is
executed.

When time is used as part of a pipeline, the times reported
are unspecified, except when it is the sole command within a
grouping command in that pipeline. For example, the commands
on the left are unspecified; those on the right report on
utilities a and c, respectively.

time a | b | c { time a } | b | c
a | b | time c a | b | (time c)

OPTIONS
The following option is supported:

-p Write the timing output to standard error in the
following format:

--还有--(28%)

[kingfire]

srand(time(0));是什么意思呀???
-----------------------------------
int k=rand();
rand()就是用来产生一个随机数的函数，其实这个随机数并不是一个生活中的真正意义上的随机数，它是靠一个算法运算出来的！
srand(int);就是给这个算法一个启动种子，也就是算法的随机种子数，有这个数以后才可以产生随机数！！！

[wenliang_d]

用1970.1.1至今的秒数，初始化随机数种子。

[HelloThis]

就是给这个算法一个启动种子，也就是算法的随机种子数，有这个数以后才可以产生随机数,
用1970.1.1至今的秒数，初始化随机数种子。

接着要用
rand();

[liushmh]

用 时间作为一个随机种子数 以便获得一个随机数

[freezingfire]

计算机没有办法产生真正的随机数的，是用算法模拟，所以你只调用rand，每次出来的东西是一样的。设置一个种子后，根据种子的不同，就可以产生不同的数了。而怎么保证种子的不同呢？最简单的办法当然是用永远在向前的时间。