ERR_ERROR_STRING(3ossl)

✨ ERR_ERROR_STRING(3ossl) ✨

okay bestie, welcome to the OpenSSL manual page for ERR_ERROR_STRING(3ossl) — yes the title is literally shouting, that's just how manpages are, they have main character energy fr 💅

💖 NAME 💖

ERR_error_string, ERR_error_string_n, ERR_lib_error_string, ERR_func_error_string, ERR_reason_error_string — bestie, these are your little translators. They take a cursed numeric error code and turn it into a human-readable error message 🫶

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🌸 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);

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🦋 DESCRIPTION 🦋

so. ERR_error_string() does the thing where it generates a human-readable string representing the error code e, and places it at buf. and like — buf must be at least 256 bytes long, no cap. if buf is NULL, the error string gets placed in a static buffer instead.

⚠️ heads up bestie: this function is not thread-safe and it does no checks on the size of the buffer. so please, for the love of everything, use ERR_error_string_n() instead 🙈

ERR_error_string_n() is the variant of ERR_error_string() that writes at most len characters (including the terminating 0) and truncates the string if necessary. and for ERR_error_string_n(), buf MUST NOT be NULL. like, that's the rule, periodt.

the string will have the following format:

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

where error code is an 8 digit hexadecimal number, and library name and reason string are ASCII text. iconic little lineup honestly ✨

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

if there is no text string registered for the given error code, the error string will contain the numeric code instead. lowkey a glow-down but it's fine, at least you get something 💀

ERR_print_errors(3) can be used to print all error codes currently in the queue. very handy, very slay 👑

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⭐ RETURN VALUES ⭐

• ERR_error_string() returns a pointer to a static buffer containing the string if buf == NULL, and buf otherwise.
• ERR_lib_error_string() and ERR_reason_error_string() return the strings, and NULL if none is registered for the error code.
• ERR_func_error_string() returns NULL. that's it. that's the whole vibe. 💀

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👀 SEE ALSO 👀

• ERR_get_error(3)
• ERR_print_errors(3)

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📜 HISTORY 📜

ERR_func_error_string() became deprecated in OpenSSL 3.0. it's giving retired 🧚

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💜 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 <https://www.openssl.org/source/license.html>.

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and that's the whole page bestie!! this one came from OpenSSL 3.5.9, dated 2026-09-29, and it lives at ERR_ERROR_STRING(3ossl) in the manual. go forth and read your error codes like the icon you are 🌈🎀💖