[SOLVED] Calling readline() makes errno 2 in C. Does anyone know about this?

Issue

While testing my code, I have found out readline makes errno 2. This is ENOENT which means No such file or directory. Does anyone know why??

#include <readline/readline.h>
#include <stdio.h>
#include <errno.h>

int main()
{
        char *a = readline("shell$");
        printf("%d\n", errno);
        while (a)
        {
                printf("%s\n", a);
                readline("shell$");
        }
}

Do I have to set errno to 2 after readline? or Is it an error?

its in Macos

compiled with this comm -> gcc -lreadline main.c

Since I am using the Mac which is provided from a kind of institution, I don't have super privileges. Maybe could it cause the error? permission thing?

Solution

If a function does not return error value (or otherwise indicate there was an error), then, generally speaking, valuenof errno is not set or reset by it.

So probably some operation done by readline had an error, but it was recoverable and readline succeeded and did not touch errno itself.

So, before checking errno, you have to check if the function failed (or otherwise is documented to set errno in some specific way), usually by checking the return value.

Answered By - hyde

Answer Checked By - Clifford M. (WPSolving Volunteer)