Meaning of dangling pointers

Question

How can I determine dangling pointers in C? Here is example of this.

int *fun(void) {
    int i = 2;
    return &i;
}

What do you mean determine? Decide if the return value of your `fun` is a dangling pointer or not? Or to pass/return the value (or address) of the `i` variable? — Emil Vatai, Oct 27 '18 at 11:22
`i` is a local variable. It doesn't exist after `fun` returns, but you're returning a pointer to it. Same if you return a pointer to malloced memory but freed the pointer before returning it. Such pointers dangle. It isn't rocket science. — Petr Skocik, Oct 27 '18 at 11:23
I meant return value of function is dangling pointer or not? — Emil, Oct 27 '18 at 11:24

score 0 · Answer 1 · answered Oct 27 '18 at 11:25

Here in below code block

int *fun(void) {
    int i = 2;
    return &i;
}

you are returning a address of a local variable that means you are returning a dangling pointer & it causes undefined behaviour, your compiler could have warned you like

error: function returns address of local variable [-Werror=return-local-addr]
     return &i;

above if you could have compile with flags like gcc -Wall -Wstrict-prototypes -Werror test.c

Meaning of dangling pointers

1 Answers1