Raw pointers

In unsafe code blocks, Rust allows the use of a new kind of pointers called raw pointers. These pointers have no built-in security, but you can work with them with the same freedom as you would with C pointers. They are written as:

• *const T for a pointer to an immutable value, or type T
• *mut T for a mutable pointer

These can point to invalid memory, and the memory resources need to be manually freed. This means that a raw pointer could inadvertently be used after freeing the memory it points to. Also, multiple concurrent threads have non-exclusive access to mutable raw pointers. Because you're not sure of its contents (at least, we have no compiler guarantee of valid content), dereferencing a raw pointer can also lead to program failure.

This is why dereferencing a raw pointer can only be done inside an unsafe block, as illustrated in the following code fragment:

// code from Chapter 10/code/raw_pointers.rs: 
let p_raw: *const u32 = &10; 
// let n = *p_raw; // compiler error...