http://man7.org/linux/man-pages/man3/random.3.html contains an error with
respect to the feature test macro requirements.
It says "_XOPEN_SOURCE >= 500
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE"
However, the POSIX-related requirement is not complete. According to POSIX, it
originated in issue 4 as an X/OPEN UNIX extension (see
http://pubs.opengroup.org/onlinepubs/9699919799/functions/random.html), and was
moved to BASE in issue 5. The GLIBC 2.12 on my RHEL6 system do seem to gate it
as POSIX says (see clips below), so it is only the man page in error.
So the man page really should say "_XOPEN_SOURCE >= 500
|| _XOPEN_SOURCE_EXTENDED && _XOPEN_SOURCE
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE"
(I'm not totally certain of the right way for _XOPEN_SOURCE_EXTENDED to be used,
but you get the idea.)
Now perhaps this extra line was purposely left out based on a statement in
feature_test_macros(7) that says "since defining _XOPEN_SOURCE with a value of
500 or more has the same effect as defining _XOPEN_SOURCE_EXTENDED, the latter
(obsolete) feature test macro is generally not described in the SYNOPSIS in man
pages." However, for this case it leaves out a user getting it with a version
older than 500. (The manual as-is is good for a new user, really, but it is not
good for a developer working on the proper gates in the code, or a user looking
at older code.)
Craig Howland
Supporting information:
From stdlib.h;
#if defined __USE_SVID || defined __USE_XOPEN_EXTENDED || defined __USE_BSD
...
extern long int random (void) __THROW;
From features.h:
#ifdef _XOPEN_SOURCE
# define __USE_XOPEN 1
# if (_XOPEN_SOURCE - 0) >= 500
# define __USE_XOPEN_EXTENDED 1
# ...
# else
# ifdef _XOPEN_SOURCE_EXTENDED
# define __USE_XOPEN_EXTENDED 1
...
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