标签:mut code height Write volatile test OS Day change
[Write an OS in Rust] Day 2
目录Today's task is implement a write function for vga text mode followed by post
Rust
Attribute
#[allow(dead_code)]
: The compiler provides a dead_code lint that will warn about unused functions. Use it allow a unused strcut、function...#[repr(u8)]
: Give a alignment.
use
Like from xxx import xxxx
in python. According to Use declarations, use
will be the top in a module or a block usually.
mut
Sometimes I can't understand mut
clearly. Today I did a new test about mut
, I wrote this code :
#[warn(dead_code)]
struct Rectangle {
height: i32,
width: i32,
}
impl Rectangle {
pub fn change_height(&mut self, val: i32) {
self.height = val;
}
}
fn main()
{
let mut test = Rectangle{
height: 10,
width: 5,
};
test.change_height(9);
}
then, compiler tell me, I need set a mutable var:
➜ hello-world git:(master) ✗ cargo build
Compiling hello-world v0.1.0 (./hello-world)
error[E0596]: cannot borrow `test` as mutable, as it is not declared as mutable
--> src/main.rs:193:5
|
188 | let test = Rectangle{
| ---- help: consider changing this to be mutable: `mut test`
...
193 | test.change_height(9);
| ^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
For more information about this error, try `rustc --explain E0596`.
error: could not compile `hello-world` due to previous error
so, the correct code is :
fn main()
{
let mut test = Rectangle{
height: 10,
width: 5,
};
test.change_height(9);
}
volatile
ablou volatile
, I also search its usages in C++.
A volatile specifier is a hint to a compiler that an object may change its value in ways not specified by the language so that aggressive optimizations must be avoided.
One variable use volatile
ask the compiler not to optimize this variable.volatile
indicates the variable maybe changed when you access, but this change maybe cant be percieved by compiler, volatile
guarent that every time you access the variable, you should access it address.
In Rust, volatile
is a crate
OS
This post just decribed VGA Text Mode.
标签:mut,code,height,Write,volatile,test,OS,Day,change 来源: https://www.cnblogs.com/yisumi/p/15959826.html
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