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@node ctime
@section ctime
@findex ctime
@c Copyright (C) 2005, 2009 Free Software Foundation, Inc.
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
@c Texts. A copy of the license is included in the ``GNU Free
@c Documentation License'' file as part of this distribution.
The @code{ctime} function need not be reentrant, and consequently is
not required to be thread safe. Implementations of @code{ctime}
typically write the time stamp into static buffer. If two threads
call @code{ctime} at roughly the same time, you might end up with the
wrong date in one of the threads, or some undefined string. There is
a re-entrant interface @code{ctime_r}, that take a pre-allocated
buffer and length of the buffer, and return @code{NULL} on errors.
The input buffer should be at least 26 bytes in size. The output
string is locale-independent. However, years can have more than 4
digits if @code{time_t} is sufficiently wide, so the length of the
required output buffer is not easy to determine. Increasing the
buffer size when @code{ctime_r} return @code{NULL} is not necessarily
sufficient. The @code{NULL} return value could mean some other error
condition, which will not go away by increasing the buffer size.
A more flexible function is @code{strftime}. However, note that it is
locale dependent.
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