error: implicit declaration of function 'rl_replace_line' is invalid in C99 [-Werror,-Wimplicit-function-declaration]

Question

I'm trying to implement rl_replace_line() in my code but when I try to compile it like that:

gcc -lreadline test.c -o test

I get this error message:

error: implicit declaration of function 'rl_replace_line' is invalid in C99 [-Werror,-Wimplicit-function-declaration]

however I think I used the good header files? here is my code:

# include <stdio.h>
# include <readline/readline.h>
# include <readline/history.h>
# include <unistd.h>
# include <stdlib.h>

char    *get_line()
{
    char *line;

    line = NULL;
    if (line)
    {
        free(line);
        line = NULL;
    }
    line = readline("Minishell>");
    if (line)
        add_history(line);
    return (line);
}

void    sig_handler(int signum)
{
    if (signum == SIGINT)
    {
        printf("\n");
        rl_on_new_line();
        rl_replace_line("", 0);
        rl_redisplay();
    }
}

int main(void)
{
    char    *line;

    signal(SIGINT, sig_handler);
    line = get_line();
    printf("%s\n", line);
}

I don't understand why it doesn't work, I hope you guys can help thanks!

Is that the only function that causes an error? Is that function declared in the readline related headers you include? Maybe that function is not available in the version of readline that you have installed. — Gerhardh, Jun 16 '21 at 13:26
Those are the only readline headers that I have found, I will try to see if it's a version issue — luweglarz, Jun 16 '21 at 13:29
Try `gcc test.c -o test -lreadline` and see if it makes a difference. Linker options should be placed after compiler options. — Lundin, Jun 16 '21 at 13:43
The `rl_replace_line` function was added in Readline-4.3 which was released in 2002. — Ian Abbott, Jun 16 '21 at 13:47
Is there a way to know what does a header file exactly contains? — luweglarz, Jun 16 '21 at 14:14
Open the header file in your favourite editor. What more do you need? — Gerhardh, Jun 16 '21 at 16:31
Sorry for the late answer I couldn't have access to the Mac, I checked in the header file of readline.h and it contains the declaration of this function — luweglarz, Jun 21 '21 at 10:40
Because I say so! and because printf() is not async-proof. https://stackoverflow.com/q/63461038/905902 — wildplasser, Jun 21 '21 at 11:49

score 1 · Accepted Answer · answered Jun 21 '21 at 11:03

1

I managed to solve my problem by including the correct path with:

-L .brew/opt/readline/lib and -I .brew/opt/readline/include

now I compile like this and it's working:

gcc test.c -o test -lreadline -L .brew/opt/readline/lib -I .brew/opt/readline/include

answered Jun 21 '21 at 11:03

luweglarz

103
2
9

1

Note this is because brew refuses to link readline. Warning: Refusing to link macOS provided/shadowed software: readline For compilers to find readline you may need to set: export LDFLAGS="-L/usr/local/opt/readline/lib" export CPPFLAGS="-I/usr/local/opt/readline/include" – Chris Feb 03 '22 at 00:20

score 1 · Answer 2 · answered Aug 20 '22 at 12:15

1

I solve the issue by finding the libreadline.a with the command ==> find / -name libreadline.a 2> /dev/null.

The result is ==> /opt/homebrew/Cellar/readline/8.1.2/lib/libreadline.a

So I put the correct path for the compilation: -L libs -lft -L /opt/homebrew/Cellar/readline/8.1.2/lib -lreadline.

No this is working perfectly

answered Aug 20 '22 at 12:15

Vess

11
3

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Aug 28 '22 at 18:51

error: implicit declaration of function 'rl_replace_line' is invalid in C99 [-Werror,-Wimplicit-function-declaration]

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