[lldb] enable stdin with stdin command

[Vipul-Cariappa]

This is a tricky implementation.
Say the program uses scanf to read input. The user will need to populate stdin before the call to scanf. Otherwise, the program will freeze, because scanf is trying to read, but stdin is not populated.

Note: Using the stdin command with gdb will raise AttributeError for now (Not implemented with the gdb backend).

Try with:

// a/fib.c
#include <stdio.h>
#include <stdlib.h>


int internal_fib(int a, int b, int n) {
    if (n < 2)
        return b;
    return internal_fib(b, a + b, n - 1);
}

int fib(int x) {
    return internal_fib(0, 1, x);
}

int main(int argc, char *argv[]) {
    int x = 2;
    printf("Enter number: ");
    scanf("%d", &x);
    printf("%d\n", fib(x));
    return 0;
}

// b/fib.c
#include <stdio.h>
#include <stdlib.h>


int internal_fib(int a, int b, int n) {
    while (--n) {
        int tmp = a;
        a = b;
        b = tmp + b;
    }
    return a;
}

int fib(int x) {
    return internal_fib(0, 1, x);
}

int main(int argc, char *argv[]) {
    int x = 2;
    printf("Enter number: ");
    scanf("%d", &x);
    printf("%d\n", fib(x));
    return 0;
}

Example:

Screencast.From.2025-03-27.11-43-27.mp4