Seeds the pseudo-random number generator used bystd::rand() with the valueseed.

Ifstd::rand() is used before any calls tosrand(),std::rand() behaves as if it was seeded withsrand(1).

Each timestd::rand() is seeded with the sameseed, it must produce the same sequence of values.

srand() is not guaranteed to be thread-safe.

[edit]Parameters

[edit]Return value

(none)

[edit]Notes

Generally speaking, the pseudo-random number generator should only be seeded once, before any calls torand(), at 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 tostd::time(0) as the seed.However,std::time returns astd::time_t value, andstd::time_t is not guaranteed to be an integral type.In practice, though, every major implementation definesstd::time_t to be an integral type, and this is also what POSIX requires.

[edit]Example

#include <cstdlib>#include <ctime>#include <iostream> int main(){    std::srand(std::time(0));// use current time as seed for random generatorstd::cout<<"Random value on [0, "<<RAND_MAX<<"]: "<<std::rand()<<'\n';}

Random value on [0, 2147483647]: 1373858591

[edit]See also

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