ERR_ERROR_STRING(3ssl) OpenSSL ERR_ERROR_STRING(3ssl) ERR_error_string, ERR_error_string_n, ERR_lib_error_string, ERR_func_error_string, ERR_reason_error_string - #include 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); OpenSSL 3.0: const char *ERR_func_error_string(unsigned long e); ERR_error_string() e buf. buf 256 . buf NULL . ERR_error_string_n() . ERR_error_string_n() ERR_error_string() len ( ) . ERR_error_string_n() buf NULL. : error:[error code]:[library name]::[reason string] 8 ASCII. ERR_lib_error_string() ERR_reason_error_string() . . ERR_print_errors(3) . ERR_error_string() buf == NULL buf. ERR_lib_error_string() ERR_reason_error_string() NULL . ERR_func_error_string() NULL. ERR_get_error(3), ERR_print_errors(3) ERR_func_error_string() OpenSSL 3.0. 2000-2017 OpenSSL. . Apache 2.0 ( ""). . LICENSE . 3 . . : . 3.6.2 7 2026 ERR_ERROR_STRING(3ssl)