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@(#)rand.3 8.1 (Berkeley) 6/4/93
$FreeBSD$
.Dd April 2, 2013 .Dt RAND 3 .Os .Sh NAME .Nm rand , .Nm srand , .Nm sranddev , .Nm rand_r .Nd bad random number generator .Sh LIBRARY .Lb libc .Sh SYNOPSIS n stdlib.h .Ft void .Fn srand "unsigned seed" .Ft void .Fn sranddev void .Ft int .Fn rand void .Ft int .Fn rand_r "unsigned *ctx" .Sh DESCRIPTION f -symbolic The functions described in this manual page are not cryptographically secure. Cryptographic applications should use .Xr arc4random 3 instead. .Ef
p These interfaces are obsoleted by .Xr random 3 .
p The .Fn rand function computes a sequence of pseudo-random integers in the range of 0 to .Dv RAND_MAX (as defined by the header file n stdlib.h ) .
p The .Fn srand function sets its argument .Fa seed as the seed for a new sequence of pseudo-random numbers to be returned by .Fn rand . These sequences are repeatable by calling .Fn srand with the same seed value.
p If no .Fa seed value is provided, the functions are automatically seeded with a value of 1.
p The .Fn sranddev function initializes a seed using pseudo-random numbers obtained from the kernel.
p The .Fn rand_r function provides the same functionality as .Fn rand . A pointer to the context value .Fa ctx must be supplied by the caller.
p For better generator quality, use .Xr random 3 or .Xr lrand48 3 . .Sh SEE ALSO .Xr arc4random 3 , .Xr lrand48 3 , .Xr random 3 , .Xr random 4 .Sh STANDARDS The .Fn rand and .Fn srand functions conform to .St -isoC .
p The .Fn rand_r function is as proposed in the POSIX.4a Draft #6 document.