Var_dump and print_r alternative in rust

help
1

Hi,

I am new to Rust. Is there a way of printing out the Structure and content of variables in the commandline similar to var_dump and print_r in PHP. It would help me a lot to understand some structs or vectors.

2

I guess this will help you :slight_smile:

https://doc.rust-lang.org/stable/book/ch05-02-example-structs.html#adding-useful-functionality-with-derived-traits

Ps. read the whole book (starting with chapter 1 (!)), if you want to learn the rust language.

3 
use std::fmt::Debug;

#[derive(Debug)]   <-  it's important
struct Point {
    x: i32,
    y: i32
}

fn main() {
    let p = Point {x:1, y:2};
    println!("{:?}",  p);
}              ^
               |_____ this important too

And if the compiler swears in the case of a more complex data structure - see the recommendation above.

4

Thanks a lot. This will help a lot.

Surprisingly I did not even have to use this at all. :? or :#? did already the job. And shame on :roll_eyes: me the compiler suggest tu use that because Display was not implemented by the crate

use std::fmt::Debug;

#[derive(Debug)]   <-  it's important
5

FYI, use std::fmt::Debug is not needed if you're deriving Debug - you only need to pull it in if you're going to implement it manually.

You also may be interested in the new-ish dbg! macro, which can be wrapped around any expression in order to print some helpful info - for example:

#[derive(Debug, PartialEq)]
struct Point {
    x: i32,
    y: i32,
}

fn main() {
    let p1 = Point { x: 1, y: 2 };
    let p2 = Point { x: 2, y: 1 };

    // dbg! returns whatever you pass in, so you can pretty much use 
    // it anywhere you'd write an expression - for example, right in the
    // middle of an if condition!
    if dbg!(p1) == dbg!(p2) {
        // Some code here...
    }
}

This would print:

[src/main.rs:11] p1 = Point {
    x: 1,
    y: 2,
}
[src/main.rs:11] p2 = Point {
    x: 2,
    y: 1,
}

Note that you get the filename, the line number, and the original expression in your output, as well as the actual value!