#include <openssl/err.h> void ERR_load_strings(int lib, ERR_STRING_DATA str[]); int ERR_get_next_error_library(void); unsigned long ERR_PACK(int lib, int func, int reason);
str is an array of error string data:
 typedef struct ERR_string_data_st
 {
        unsigned long error;
        char *string;
 } ERR_STRING_DATA;
The error code is generated from the library number and a function and reason code: error = ERR_PACK(lib, func, reason). ERR_PACK() is a macro.
The last entry in the array is {0,0}.
ERR_get_next_error_library() can be used to assign library numbers to user libraries at runtime.