# Learning zig: stack and dangling pointers

**URL:** <https://ziggit.dev/t/learning-zig-stack-and-dangling-pointers/2332>\
**Category:** Help\
**Tags:** memory-management\
**Created:** [December 1, 2023, 5:01pm UTC](https://ziggit.dev/t/learning-zig-stack-and-dangling-pointers/2332 "2023-12-01T17:01:39Z")\
**Posts on this page:** 1\
**Showing post:** 5

<div class="post-metadata">

**Author:** ![tgirod](https://ziggit.dev/user_avatar/ziggit.dev/tgirod/32/3744_2.png) [@tgirod](https://ziggit.dev/u/tgirod)\
**Post date:** [December 1, 2023, 5:59pm UTC](https://ziggit.dev/t/learning-zig-stack-and-dangling-pointers/2332/5 "2023-12-01T17:59:10Z")

</div>

hey @AndrewCodeDev, thanks for the quick reply!

So, I got some of it right - v is discarded at the end of `init`, so `&v` is a dangling pointer. But there are still things mysterious.

Here is another example:

```zig
const std = @import("std");

const Box = struct {
    value: *const u64,

    fn one(v: u64) Box {
        std.debug.print("address of parameter v {}\n", .{&v});
        return .{
            .value = &v,
        };
    }

    fn two(v: u64) Box {
        var tmp = v;
        std.debug.print("address of var tmp {}\n", .{&tmp});
        return .{
            .value = &tmp,
        };
    }
};

pub fn main() void {
    const one = Box.one(23);
    std.debug.print("box one {}\n\n", .{one});
    const two = Box.two(23);
    std.debug.print("box two {}\n", .{two});
}

```

resulting in:

```sh
> zig run mem.zig
address of parameter v u64@7ffe80c80188
box one mem.Box{ .value = u64@7ffe80c80198 }

address of var tmp u64@7ffe80c80190
box two mem.Box{ .value = u64@7ffe80c80190 }

```

So here, when I’m using the address of the parameter directly inside of the Box, it gets changed. Whereas if I copy the value to `tmp` and use that address, it stays the same.

So I guess the compiler is doing something clever when using the address of a parameter in a function?

---

_[View the full topic](https://ziggit.dev/t/learning-zig-stack-and-dangling-pointers/2332)._