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@deftypefun {char *} strerror (int @var{errnum})
@standards{ISO, string.h}
@safety{@prelim{}@mtunsafe{@mtasurace{:strerror}}@asunsafe{@ascuheap{} @ascuintl{}}@acunsafe{@acsmem{}}}
@c Calls strerror_r with a static buffer allocated with malloc on the
@c first use.
The @code{strerror} function maps the error code (@pxref{Checking for
Errors}) specified by the @var{errnum} argument to a descriptive error
message string.  The return value is a pointer to this string.

The value @var{errnum} normally comes from the variable @code{errno}.

You should not modify the string returned by @code{strerror}.  Also, if
you make subsequent calls to @code{strerror}, the string might be
overwritten.  (But it's guaranteed that no library function ever calls
@code{strerror} behind your back.)

The function @code{strerror} is declared in @file{string.h}.
@end deftypefun

@deftypefun {char *} strerror_r (int @var{errnum}, char *@var{buf}, size_t @var{n})
@standards{GNU, string.h}
@safety{@prelim{}@mtsafe{}@asunsafe{@ascuintl{}}@acunsafe{}}
The @code{strerror_r} function works like @code{strerror} but instead of
returning the error message in a statically allocated buffer shared by
all threads in the process, it returns a private copy for the
thread.  This might be either some permanent global data or a message
string in the user supplied buffer starting at @var{buf} with the
length of @var{n} bytes.

At most @var{n} characters are written (including the NUL byte) so it is
up to the user to select a buffer large enough.

This function should always be used in multi-threaded programs since
there is no way to guarantee the string returned by @code{strerror}
really belongs to the last call of the current thread.

The function @code{strerror_r} is a GNU extension and it is declared in
@file{string.h}.
@end deftypefun

@deftypefun void perror (const char *@var{message})

error: patch failed: manual/errno.texi:1147
error: manual/errno.texi: patch does not apply