.\"	$OpenBSD: ERR_error_string.3,v 1.7 2018/03/27 17:35:50 schwarze Exp $
.\"	OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
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.\" This file was written by Ulf Moeller <ulf@openssl.org>.
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.Dd $Mdocdate: March 27 2018 $
.Dt ERR_ERROR_STRING 3
.Os
.Sh NAME
.Nm ERR_error_string ,
.Nm ERR_error_string_n ,
.Nm ERR_lib_error_string ,
.Nm ERR_func_error_string ,
.Nm ERR_reason_error_string
.Nd obtain human-readable OpenSSL error messages
.Sh SYNOPSIS
.In openssl/err.h
.Ft char *
.Fo ERR_error_string
.Fa "unsigned long e"
.Fa "char *buf"
.Fc
.Ft void
.Fo ERR_error_string_n
.Fa "unsigned long e"
.Fa "char *buf"
.Fa "size_t len"
.Fc
.Ft const char *
.Fo ERR_lib_error_string
.Fa "unsigned long e"
.Fc
.Ft const char *
.Fo ERR_func_error_string
.Fa "unsigned long e"
.Fc
.Ft const char *
.Fo ERR_reason_error_string
.Fa "unsigned long e"
.Fc
.Sh DESCRIPTION
.Fn ERR_error_string
generates a human-readable string representing the error code
.Fa e
and places it in
.Fa buf .
.Fa buf
must be at least 256 bytes long.
If
.Fa buf
is
.Dv 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
.Fn ERR_error_string_n
instead.
.Pp
.Fn ERR_error_string_n
is a variant of
.Fn ERR_error_string
that writes at most
.Fa len
characters (including the terminating NUL) and truncates the string
if necessary.
For
.Fn ERR_error_string_n ,
.Fa buf
may not be
.Dv NULL .
.Pp
The string will have the following format:
.Pp
.Dl error:[error code]:[library name]:[function name]:[reason string]
.Pp
The error code is an 8-digit hexadecimal number.
The library name, the function name, and the reason string are ASCII
text.
.Pp
.Fn ERR_lib_error_string ,
.Fn ERR_func_error_string ,
and
.Fn ERR_reason_error_string
return the library name, the function name, and the reason string,
respectively.
.Pp
The OpenSSL error strings should be loaded by calling
.Xr ERR_load_crypto_strings 3
or, for SSL applications,
.Xr SSL_load_error_strings 3
first.
If there is no text string registered for the given error code, the
error string will contain the numeric code.
.Pp
.Xr ERR_print_errors 3
can be used to print all error codes currently in the queue.
.Sh RETURN VALUES
.Fn ERR_error_string
returns a pointer to a static buffer containing the string if
.Fa buf
is
.Dv NULL ,
or
.Fa buf
otherwise.
.Pp
.Fn ERR_lib_error_string ,
.Fn ERR_func_error_string ,
and
.Fn ERR_reason_error_string
return the strings, or
.Dv NULL
if none is registered for the error code.
.Sh SEE ALSO
.Xr ERR 3 ,
.Xr ERR_get_error 3 ,
.Xr ERR_load_crypto_strings 3 ,
.Xr ERR_print_errors 3 ,
.Xr SSL_load_error_strings 3
.Sh HISTORY
.Fn ERR_error_string ,
.Fn ERR_lib_error_string ,
.Fn ERR_func_error_string ,
and
.Fn ERR_reason_error_string
first appeared in SSLeay 0.4.4 and have been available since
.Ox 2.4 .
.Pp
.Fn ERR_error_string_n
first appeared in OpenSSL 0.9.6 and has been available since
.Ox 2.9 .