memshuffle(3pub) [debian man page]

MEMSHUFFLE(3pub)					       C Programmer's Manual						  MEMSHUFFLE(3pub)

NAME

       memshuffle - make an array be in random order

SYNOPSIS

       #include <publib.h>
       void *memshuffle(void *block, size_t elsize, size_t elnum);

DESCRIPTION

       memshuffle will move around the elements of an array in a random fashion.  It uses the standard library function rand(3) to get the pseudo-
       random numbers it needs.  The caller must set a suitable seed with srand(3).

RETURN VALUE

       memshuffle returns its first argument.

EXAMPLE

       To shuffle an integer array one might do the following.

	    int array[4] = { 1, 2, 3, 4 };

	    memshuffle(array, sizeof(array[0]), 4);

BUGS

       On many systems rand(3) is not of very good quality.  However, it is the only random number generator that can be assumed to exist.  Making
       it possible for the caller to provide an alternate source of random numbers (e.g., via a function pointer) is perhaps too more trouble than
       its worth.  A better way would be for everyone to fix their rand's.

SEE ALSO

       publib(3), memrev(3), rand(3), srand(3)

AUTHOR

       Lars Wirzenius (lars.wirzenius@helsinki.fi)

Publib							       C Programmer's Manual						  MEMSHUFFLE(3pub)

RAND(3) 						   BSD Library Functions Manual 						   RAND(3)

NAME

     rand, rand_r, srand, sranddev -- bad random number generator

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdlib.h>

     int
     rand(void);

     int
     rand_r(unsigned *seed);

     void
     srand(unsigned seed);

     void
     sranddev(void);

DESCRIPTION

     These interfaces are obsoleted by random(3).

     The rand() function computes a sequence of pseudo-random integers in the range of 0 to RAND_MAX (as defined by the header file <stdlib.h>).

     The srand() function sets its argument seed as the seed for a new sequence of pseudo-random numbers to be returned by rand().  These
     sequences are repeatable by calling srand() with the same seed value.

     If no seed value is provided, the functions are automatically seeded with a value of 1.

     The sranddev() function initializes a seed, using the random(4) random number device which returns good random numbers, suitable for crypto-
     graphic use.

     The rand_r() function provides the same functionality as rand().  A pointer to the context value seed must be supplied by the caller.

SEE ALSO

     random(3), random(4)

STANDARDS

     The rand() and srand() functions conform to ISO/IEC 9899:1990 (``ISO C90'').

     The rand_r() function is as proposed in the POSIX.4a Draft #6 document.

BSD
								   May 25, 1999 							       BSD