Background
Let us share some of the formatting expressions that are supported in Rust.
Format Macros
| Macro | Intent | Example |
|---|---|---|
| format! | Emits output to a string | let buffer:String; buffer = format!(“{0} plus {1} equals {2}”, 1,2, 1+2); |
| write! | Emits output to a file handle | |
| writeln! | Emits output to a file handle and adds a new line | |
| print! | Emits output to standard output | |
| println! | Emits output to standard output and adds a new line | println!(“{0:10.3}”, 22 as f64 / 7 as f64); |
| eprint! | Emits output to standard error | |
| eprintln! | Emits output to standard error and adds a new line | let filename:&str = “b:\\fileNoPresent.txt”; eprintln!(“Error: Could not openfile {0}”, filename); |
| format_args! | Used to pass around a format strings |
Building Out a Format String
Positional Parameters
In bare, a format tag is repersented as {}.
Based on which argument will be represented it’s place in the argument list is referenced.
The first argument is 0 (zero ).
Here is a basic example:-
println!
(
"Number 1 ( {0} ) divide Number 2 ( {1} ) is {2}"
, number_1_float
, number_2_float
, result_float
);
Explanation:-
- {0}:- number_1_float
- {1}:- number_2_float
- {2}:- result_float
Formatting Tags
| Data Type | Intent | Expression | Result |
|---|---|---|---|
| Float | |||
| Plain number | {2} | 3.142857142857143 | |
| three (3) decimal places | {2:.3} | 3.143 | |
| width of 10, and three (3) decimal places | {2:10.3} | 3.143 | |
| width of 10 – 0 left padded, and three (3) decimal places | {2:010.3} | 000003.143 | |
| String | |||
| Character size 15, left ( < ) aligned | [{4:<15}] | [55101 ] | |
| Character size 15, right ( < ) aligned | [{4:>15}] | [ 55101] | |
| Character size 15, middle ( < ) aligned | [{4:^15}] | [ 55101 ] | |
Script
Code
/*
Declare "Module" Constants
*/
const CHAR_EQUAL:char = '=';
fn repeatChar(ch: char, n:usize) -> String
{
return
(
ch.to_string()
).repeat(n);
}
fn main()
{
let number_1_float:i32 = 22;
let number_2_float:i32 = 7;
let result_float:f64;
let mut format:String;
let header_address_fullname:&str = "Name";
let header_address_address:&str = "Address";
let header_address_city:&str = "City";
let header_address_state:&str = "State";
let header_address_postal_code:&str = "Postal Code";
let header_address_fullname_underline:String
= repeatChar
(
CHAR_EQUAL
, header_address_fullname.chars().count()
).to_string();
let header_address_address_underline:String
= repeatChar
(
CHAR_EQUAL
, header_address_address.chars().count()
).to_string();
let header_address_city_underline:String
= repeatChar
(
CHAR_EQUAL
, header_address_city.chars().count()
).to_string();
let header_address_state_underline:String
= repeatChar
(
CHAR_EQUAL
, header_address_state.chars().count()
).to_string();
let header_address_postal_code_underline:String
= repeatChar
(
CHAR_EQUAL
, header_address_postal_code.chars().count()
).to_string();
let mut fullname_1:&str;
let mut address_1:&str;
let mut city_1:&str;
let mut state_1:&str;
let mut postal_code_1:&str;
let mut fullname_2:&str;
let mut address_2:&str;
let mut city_2:&str;
let mut state_2:&str;
let mut postal_code_2:&str;
result_float = number_1_float as f64 / number_2_float as f64 ;
fullname_1 = "John Smith";
address_1 = "1021 Brinson Street";
city_1 = "St Paul";
state_1 = "MN";
postal_code_1 = "55101";
fullname_2 = "Angie Stone";
address_2 = "7181 Ridgewood Drive";
city_2 = "Rochestor";
state_2 = "NY";
postal_code_2 = "14602";
println!(
"Number 1 ( {0} ) divide Number 2 ( {1} ) is {2}"
, number_1_float
, number_2_float
, result_float
);
println!();
/*
{Position:.3}
*/
format=r"position:.decimalPlaces ( {2:.3} )".to_string();
println!(
"Number 1 ( {0} ) divide Number 2 ( {1} ) is {2:.3}. \
Format as {3}"
, number_1_float
, number_2_float
, result_float
, format
);
println!();
/*
format!("{:04}", 42); // => "0042" with leading zeros
*/
format=r"position:length.decimalPlaces ( {2:10.3} )".to_string();
println!(
"Number 1 ( {0} ) divide Number 2 ( {1} ) is {2:10.3}. \
Format as {3}"
, number_1_float
, number_2_float
, result_float
, format
);
println!();
/*
Left Align
*/
println!("Left Justify");
println!();
println!(
"{0:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, header_address_fullname
, header_address_address
, header_address_city
, header_address_state
, header_address_postal_code
);
println!(
"{0:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, header_address_fullname_underline
, header_address_address_underline
, header_address_city_underline
, header_address_state_underline
, header_address_postal_code_underline
);
println!(
"{:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, fullname_1
, address_1
, city_1
, state_1
, postal_code_1
);
println!(
"{:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, fullname_2
, address_2
, city_2
, state_2
, postal_code_2
);
println!();
println!();
/*
Right Align
*/
println!("Right Justify");
println!();
println!(
"{0:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, header_address_fullname
, header_address_address
, header_address_city
, header_address_state
, header_address_postal_code
);
println!(
"{0:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, header_address_fullname_underline
, header_address_address_underline
, header_address_city_underline
, header_address_state_underline
, header_address_postal_code_underline
);
println!(
"{:>30} {1:>30} {2:>25} {3:>10} {4:>15}"
, fullname_1
, address_1
, city_1
, state_1
, postal_code_1
);
println!(
"{:>30} {1:>30} {2:>25} {3:>10} {4:>15}"
, fullname_2
, address_2
, city_2
, state_2
, postal_code_2
);
println!();
println!();
/*
Center Align
*/
println!("Center Justify");
println!();
println!(
"{0:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, header_address_fullname
, header_address_address
, header_address_city
, header_address_state
, header_address_postal_code
);
println!(
"{0:<30} {1:<30} {2:<25} {3:<10} {4:<15}"
, header_address_fullname_underline
, header_address_address_underline
, header_address_city_underline
, header_address_state_underline
, header_address_postal_code_underline
);
println!(
"{:^30} {1:^30} {2:^25} {3:^10} {4:^15}"
, fullname_1
, address_1
, city_1
, state_1
, postal_code_1
);
println!(
"{:^30} {1:^30} {2:^25} {3:^10} {4:^15}"
, fullname_2
, address_2
, city_2
, state_2
, postal_code_2
);
println!();
println!();
}
Output
Image
Textual
Number 1 ( 22 ) divide Number 2 ( 7 ) is 3.142857142857143
Number 1 ( 22 ) divide Number 2 ( 7 ) is 3.143. Format as position:.decimalPlaces ( {2:.3} )
Number 1 ( 22 ) divide Number 2 ( 7 ) is 3.143. Format as position:length.decimalPlaces ( {2:10.3} )
Left Justify
Name Address City State Postal Code
==== ======= ==== ===== ===========
John Smith 1021 Brinson Street St Paul MN 55101
Angie Stone 7181 Ridgewood Drive Rochestor NY 14602
Right Justify
Name Address City State Postal Code
==== ======= ==== ===== ===========
John Smith 1021 Brinson Street St Paul MN 55101
Angie Stone 7181 Ridgewood Drive Rochestor NY 14602
Center Justify
Name Address City State Postal Code
==== ======= ==== ===== ===========
John Smith 1021 Brinson Street St Paul MN 55101
Angie Stone 7181 Ridgewood Drive Rochestor NY 14602
Online Source Code
OnlineGDB
- rustFormatExpressions.rs
Link
Source Code Control
GitLab
- Rust – Formatting Expressions
Link- Files
rust_format_expressions_day_01.rs
- Files
Learning in the Open 