Rust_2025：阶段1：day7.2unsafe ， 链接相关

unsafe

1. 是一个作用域块
2. 提示编译器不用对作用域块内的操作进行检查

unsafe fn modify_by_address(address: usize) {// TODO: Fill your safety notice of the code block below to match your// code's behavior and the contract of this function. You may use the// comment of the test below as your format reference.unsafe {//todo!("Your code goes here")let ptr = address as *mut u32 ;*ptr = 0xAABBCCDD;}
}#[cfg(test)]
mod tests {use super::*;#[test]fn test_success() {let mut t: u32 = 0x12345678;// SAFETY: The address is guaranteed to be valid and contains// a unique reference to a `u32` local variable.unsafe { modify_by_address(&mut t as *mut u32 as usize) };assert!(t == 0xAABBCCDD);}
}

3. 当对一个引用转换为*mut u32时，这时候的值就是地址了。
4. 对地址解引用就可以直接操作内存。

将指针转换为Box

unsafe fn raw_pointer_to_box(ptr: *mut Foo) -> Box<Foo> {// SAFETY: The `ptr` contains an owned box of `Foo` by contract. We// simply reconstruct the box from that pointer.let mut ret: Box<Foo> = unsafe { let mut ret = Box::from_raw(ptr);ret.b = Some("hello".to_owned());ret};//todo!("The rest of the code goes here")ret
}

• 实现了由不安全到安全的转变

链接 ，全局符号

extern "Rust" {fn my_demo_function(a: u32) -> u32;#[link_name = "my_demo_function"]fn my_demo_function_alias(a: u32) -> u32;
}mod Foo {// No `extern` equals `extern "Rust"`.#[no_mangle]fn my_demo_function(a: u32) -> u32 {a}
}#[cfg(test)]
mod tests {use super::*;#[test]fn test_success() {// The externally imported functions are UNSAFE by default// because of untrusted source of other languages. You may// wrap them in safe Rust APIs to ease the burden of callers.//// SAFETY: We know those functions are aliases of a safe// Rust function.unsafe {my_demo_function(123);my_demo_function_alias(456);}}
}

1. extern是全局符号，声明里面的符号是全局符号
2. 但这时候函数的符号并不是自己的名字，而是加了一些修饰。在定义函数的地方添加#[no_mangle]就可以成功链接
3. 在全局符号声明中使用#[link_name = “my_demo_function”]可以给符号改名。