Get defines dynamically for messages

Question

In this following code, i want to use predefined message for my errors_manager function, with the macro CALL_MSG(). but when i use an variable, i can't get the content of the variable !

err = ILLOPS = 1;
CALL_MSG(err)
error: ‘MSG_err’ undeclared (first use in this function)

but when i use a integer that work prefectly :/

ft_putstr(CALL_MSG(err));
print: illegal option --

How i can made a similar system for my messages (Using defines and enums if possible)

errors.h

#ifndef ERRORS_H
# define ERRORS_H

# define CALL_MSG(var) MSG_ ## var
# define MSG_1 "illegal option -- "

enum            e_errors
{
    NOT,
    ILLOPS = 1,
    ILLOPS_QUIT = 1,
    NFOUND
};

typedef enum e_errors t_errors;

#endif

main.c

void            err_manager(int errnum, t_errors err)
{
    ft_putstr("\033[91mls: ");
    if (err != 0)
        ft_putstr(CALL_MSG(err));
    if (errno != 0)
        ft_putendl(strerror(errno));
    ft_putstr("\033[0m");
    errnum = errnum;
    return ;
}

int     main(int ac, char **av, char **env)
{
    printf("Vous avez %d arguments\n", ac - 1);
    printf("PWD: %s\n", get_pwd(env));
    printf("Valeur du masque: %08x\n", mask_creator(ac, av));
}

Thanks !

Wintermute Wintermute · Accepted Answer · 2014-11-29T03:12:41

You cannot do this with macros and variables. Macros are expanded by the preprocessor before the code goes to the compiler; they don't exist at runtime, when variables get their value.

What you can do is to keep the strings in a runtime-accessible fashion, such as an array:

errors.h

char const *call_msg(t_errors err);

errors.c

char const *call_msg(t_errors err) {
  static char const *const messages[] = {
    "success -- ", // or whatever NOT is supposed to mean
    "illegal option -- ",
    "not found -- ",
    ...
  };

  check_if_err_is_within_array_bounds(err); // exercise for the reader

  return messages[err];
}

main.c

ft_putstr(call_msg(err));

Get defines dynamically for messages

errors.h

main.c

1 Answers