Local variable values and Address getting retained even after function completes Execution

Question

#include<stdio.h>
int main()
{
        int var=100;
        int *ptr=&var;
        fun(&ptr);
        printf("%p",ptr);
        printf("%d\n",*ptr);
}
int fun(int **var)
{
    int j=10;
    *var=&j;
    printf("%p\n",*var);
    printf("%d\n",**var);
}

Output:

0x7fff2c96dba4 10 0x7fff2c96dba4 10

How is value getting retained even after function completing execution? I executed it several times in gcc and in online compiler it gives the same result. please help me in understanding this...Thanks In advance.

Answer 1

How is value getting retained even after function completing execution?

Undefined behavior (UB). It might appear to "work", but that is not specified to be so by C.

fun(&ptr); runs fine, yet printf("%p",ptr); is UB as the value ptr is no longer valid. Many systems will tolerate this UB.

De-referencing ptr, with printf("%d\n",*ptr); is even worse UB. More likely to behave badly. Best not to attempt either of these.