This version of this document is no longer maintained. For the latest documentation, see http://www.qnx.com/developers/docs. |
Generate a pseudo-random number from the default state
#include <stdlib.h> long random( void );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
This function is in libc.a, but not in libc.so (in order to save space). |
The random() function uses a nonlinear additive feedback random-number generator employing a default state array size of 31 long integers to return successive pseudo-random numbers in the range from 0 to 231-1. The period of this random-number generator is approximately 16 × (231-1). The size of the state array determines the period of the random-number generator. Increasing the state array size increases the period.
Use this function in conjunction with the following:
The random() and srandom() functions have (almost) the same calling sequence and initialization properties as rand() and srand() The difference is that rand() produces a much less random sequence. In fact, the low dozen bits generated by rand() go through a cyclic pattern. All the bits generated by random() are usable. For example,
random()&01
produces a random binary value.
Unlike srand(), srandom() doesn't return the old seed because the amount of state information used is much more than a single word. The initstate() and setstate() routines are provided to deal with restarting/changing random number generators. With 256 bytes of state information, the period of the random-number generator is greater than 269.
Like rand(), random() produces by default a sequence of numbers that can be duplicated by calling srandom() with 1 as the seed.
If initstate() hasn't been called, random() behaves as though initstate() had been called with seed=1 and size=128.
If initstate() is called with size less than 8, random() uses a simple linear congruential random number generator.
The generated pseudo-random number.
See initstate().
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | No |
Signal handler | Yes |
Thread | No |
drand48(), initstate(), rand(), setstate(), srand(), srandom()