Rust ffi pointer does not panic when out of bounds

For some reason, when I run the code below, it does not panic or throw any errors…?

Isn’t this a seg fault?

Why is this happening? How do I check the size of the passed pointer to avoid panics? (without the user having to pass a "size" variable as well)

#[repr(C)]
pub struct MyStruct {
    pub item: u32
    // a bunch of other fields as well
}

#[no_mangle]
pub unsafe extern fn do_something(mut data: *mut MyStruct) {
    println!("{:p}", data);
    data= data.offset(100);
    println!("{:p}", data);
    println!("{}", (*data).item);
    if data.is_null() {
        println!("datais null");
    }
}

After I build, (and generate header using cbindgen) I link and use in a sample program like so:

#include "my_bindings.h"
int main() {
    MyStruct *data = new MyStruct[2];
    do_something(data);
    return 0;
}

This is the output I get:

0x55f0ba739eb0
0x55f0ba73a108
0

>Solution :

An out of bounds access is not necessarily a segmentation fault, it’s just an unidentified behaviour, the data that’s out of bounds may still be a part of your application so the OS won’t kill your application.

Unfortunately this is unsafe code, so rust can’t do anything about it, and you should wrap it in a safer rust container along with the container length (you must pass the length), that panic on out of bounds access, as in the following answer Creating a Vec in Rust from a C array pointer and safely freeing it?