srand
Defined in header
<stdlib.h>
|
||
void srand( unsigned seed );
|
||
Seeds the pseudo-random number generator used by rand() with the value seed
.
If rand()
is used before any calls to srand()
, rand()
behaves as if it was seeded with srand(1)
.
Each time rand()
is seeded with the same seed
, it must produce the same sequence of values.
srand()
is not guaranteed to be thread-safe.
Contents |
[edit] Parameters
seed | - | the seed value |
[edit] Return value
(none)
[edit] Notes
Generally speaking, the pseudo-random number generator should only be seeded once, before any calls to rand()
, and the start of the program.
It should not be repeatedly seeded, or reseeded every time you wish to generate a new batch of pseudo-random numbers.
Standard practice is to use the result of a call to time(0) as the seed.
However, time()
returns a time_t value, and time_t
is not guaranteed to be an integral type.
In practice, though, every major implementation defines time_t
to be an integral type, and this is also what POSIX requires.
[edit] Example
Possible output:
Random value on [0 2147483647]: 1373858591
[edit] References
- C11 standard (ISO/IEC 9899:2011):
-
- 7.22.2.2 The srand function (p: 346-347)
- C99 standard (ISO/IEC 9899:1999):
-
- 7.20.2.2 The srand function (p: 312-313)
- C89/C90 standard (ISO/IEC 9899:1990):
-
- 4.10.2.2 The srand function
[edit] See also
generates a pseudo-random number (function) |
|
maximum possible value generated by rand() (macro constant) |
|
C++ documentation for srand
|