This section describes the random number functions that are part of the ISO C standard.
To use these facilities, you should include the header file `stdlib.h' in your program.
rand
function can return. In the GNU library, it is
2147483647
, which is the largest signed integer representable in
32 bits. In other libraries, it may be as low as 32767
.
rand
function returns the next pseudo-random number in the
series. The value ranges from 0
to RAND_MAX
.
rand
before a seed has been
established with srand
, it uses the value 1
as a default
seed.
To produce a different pseudo-random series each time your program is
run, do srand (time (0))
.
POSIX.1 extended the C standard functions to support reproducible random numbers in multi-threaded programs. However, the extension is badly designed and unsuitable for serious work.
RAND_MAX
just as rand
does. However, all its state is stored in the
seed argument. This means the RNG's state can only have as many
bits as the type unsigned int
has. This is far too few to
provide a good RNG.
If your program requires a reentrant RNG, we recommend you use the reentrant GNU extensions to the SVID random number generator. The POSIX.1 interface should only be used when the GNU extensions are not available.
Go to the first, previous, next, last section, table of contents.