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=head1 NAME

ERR_error_string, ERR_error_string_n, ERR_lib_error_string,
ERR_func_error_string, ERR_reason_error_string - obtain human-readable
error message

=head1 SYNOPSIS

 #include <openssl/err.h>

 char *ERR_error_string(unsigned long e, char *buf);
 void ERR_error_string_n(unsigned long e, char *buf, size_t len);

 const char *ERR_lib_error_string(unsigned long e);
 const char *ERR_reason_error_string(unsigned long e);

Deprecated in OpenSSL 3.0:

 const char *ERR_func_error_string(unsigned long e);

=head1 DESCRIPTION

ERR_error_string() generates a human-readable string representing the
error code I<e>, and places it at I<buf>. I<buf> must be at least 256
bytes long. If I<buf> is B<NULL>, the error string is placed in a
static buffer.
Note that this function is not thread-safe and does no checks on the size
of the buffer; use ERR_error_string_n() instead.

ERR_error_string_n() is a variant of ERR_error_string() that writes
at most I<len> characters (including the terminating 0)
and truncates the string if necessary.
For ERR_error_string_n(), I<buf> may not be B<NULL>.

The string will have the following format:

 error:[error code]:[library name]::[reason string]

I<error code> is an 8 digit hexadecimal number, I<library name> and
I<reason string> are ASCII text.

ERR_lib_error_string() and ERR_reason_error_string() return the library
name and reason string respectively.

If there is no text string registered for the given error code,
the error string will contain the numeric code.

L<ERR_print_errors(3)> can be used to print
all error codes currently in the queue.

=head1 RETURN VALUES

ERR_error_string() returns a pointer to a static buffer containing the
string if I<buf> B<== NULL>, I<buf> otherwise.

ERR_lib_error_string() and ERR_reason_error_string() return the strings,
and B<NULL> if none is registered for the error code.

ERR_func_error_string() returns NULL.

=head1 SEE ALSO

L<ERR_get_error(3)>,
L<ERR_print_errors(3)>

=head1 HISTORY

ERR_func_error_string() became deprecated in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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