mirror of https://github.com/mkerrisk/man-pages
193 lines
4.9 KiB
Groff
193 lines
4.9 KiB
Groff
.\" Copyright 2008 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\"
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.TH RANDOM_R 3 2017-09-15 "GNU" "Linux Programmer's Manual"
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.SH NAME
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random_r, srandom_r, initstate_r, setstate_r \- reentrant
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random number generator
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.PP
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.BI "int random_r(struct random_data *" buf ", int32_t *" result );
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.PP
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.BI "int srandom_r(unsigned int " seed ", struct random_data *" buf );
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.PP
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.BI "int initstate_r(unsigned int " seed ", char *" statebuf ,
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.BI " size_t " statelen ", struct random_data *" buf );
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.PP
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.BI "int setstate_r(char *" statebuf ", struct random_data *" buf );
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.fi
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.PP
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.PP
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.ad l
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.BR random_r (),
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.BR srandom_r (),
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.BR initstate_r (),
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.BR setstate_r ():
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.RS 4
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/* Glibc since 2.19: */ _DEFAULT_SOURCE
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|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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.RE
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.ad b
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.SH DESCRIPTION
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These functions are the reentrant equivalents
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of the functions described in
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.BR random (3).
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They are suitable for use in multithreaded programs where each thread
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needs to obtain an independent, reproducible sequence of random numbers.
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.PP
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The
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.BR random_r ()
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function is like
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.BR random (3),
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except that instead of using state information maintained
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in a global variable,
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it uses the state information in the argument pointed to by
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.IR buf ,
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which must have been previously initialized by
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.BR initstate_r ().
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The generated random number is returned in the argument
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.IR result .
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.PP
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The
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.BR srandom_r ()
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function is like
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.BR srandom (3),
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except that it initializes the seed for the random number generator
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whose state is maintained in the object pointed to by
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.IR buf ,
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which must have been previously initialized by
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.BR initstate_r (),
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instead of the seed associated with the global state variable.
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.PP
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The
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.BR initstate_r ()
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function is like
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.BR initstate (3)
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except that it initializes the state in the object pointed to by
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.IR buf ,
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rather than initializing the global state variable.
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Before calling this function, the
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.IR buf.state
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field must be initialized to NULL.
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The
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.BR initstate_r ()
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function records a pointer to the
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.I statebuf
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argument inside the structure pointed to by
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.IR buf .
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Thus,
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.IR statebuf
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should not be deallocated so long as
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.IR buf
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is still in use.
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(So,
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.I statebuf
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should typically be allocated as a static variable,
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or allocated on the heap using
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.BR malloc (3)
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or similar.)
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.PP
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The
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.BR setstate_r ()
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function is like
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.BR setstate (3)
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except that it modifies the state in the object pointed to by
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.IR buf ,
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rather than modifying the global state variable.
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\fIstate\fP must first have been initialized
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using
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.BR initstate_r ()
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or be the result of a previous call of
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.BR setstate_r ().
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.SH RETURN VALUE
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All of these functions return 0 on success.
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On error, \-1 is returned, with
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.I errno
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set to indicate the cause of the error.
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.SH ERRORS
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.TP
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.B EINVAL
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A state array of less than 8 bytes was specified to
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.BR initstate_r ().
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.TP
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.B EINVAL
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The
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.I statebuf
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or
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.I buf
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argument to
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.BR setstate_r ()
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was NULL.
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.TP
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.B EINVAL
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The
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.I buf
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or
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.I result
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argument to
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.BR random_r ()
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was NULL.
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.TS
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allbox;
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lbw27 lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR random_r (),
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.BR srandom_r (),
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.br
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.BR initstate_r (),
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.BR setstate_r ()
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T} Thread safety MT-Safe race:buf
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.TE
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.SH CONFORMING TO
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These functions are nonstandard glibc extensions.
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.\" These functions appear to be on Tru64, but don't seem to be on
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.\" Solaris, HP-UX, or FreeBSD.
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.SH BUGS
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The
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.BR initstate_r ()
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interface is confusing.
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.\" FIXME . https://sourceware.org/bugzilla/show_bug.cgi?id=3662
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It appears that the
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.IR random_data
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type is intended to be opaque,
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but the implementation requires the user to either initialize the
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.I buf.state
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field to NULL or zero out the entire structure before the call.
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.SH SEE ALSO
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.BR drand48 (3),
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.BR rand (3),
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.BR random (3)
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