Formatting

Formatting

Positional arguments

1.🌟🌟

1. /* Fill in the blanks */
2. fn main() {
3. println!("{0}, this is {1}. {1}, this is {0}", "Alice", "Bob"); // => Alice, this is Bob. Bob, this is Alice
4. assert_eq!(format!("{1}{0}", 1, 2), __);
5. assert_eq!(format!(__, 1, 2), "2112");
6. println!("Success!");
7. }

Named arguments

2.🌟🌟

1. fn main() {
2. println!("{argument}", argument = "test"); // => "test"

4. /* Fill in the blanks */
5. assert_eq!(format!("{name}{}", 1, __), "21");
6. assert_eq!(format!(__,a = "a", b = 'b', c = 3 ), "a 3 b");

8. /* Fix the error */
9. // Named argument must be placed after other arguments
10. println!("{abc} {1}", abc = "def", 2);

12. println!("Success!");
13. }

Padding with string

3.🌟🌟 By default, you can pad string with spaces

1. fn main() {
2. // The following two are padding with 5 spaces
3. println!("Hello {:5}!", "x"); // =>  "Hello x    !"
4. println!("Hello {:1$}!", "x", 5); // =>  "Hello x    !"

6. /* Fill in the blanks */
7. assert_eq!(format!("Hello __!", 5, "x"), "Hello x    !");
8. assert_eq!(format!("Hello __!", "x", width = 5), "Hello x    !");

10. println!("Success!");
11. }

4.🌟🌟🌟 Left align, right align, pad with specified characters.

1. fn main() {
2. // Left align
3. println!("Hello {:<5}!", "x"); // => Hello x    !
4. // Right align
5. assert_eq!(format!("Hello __!", "x"), "Hello     x!");
6. // Center align
7. assert_eq!(format!("Hello __!", "x"), "Hello   x  !");

9. // Left align, pad with '&'
10. assert_eq!(format!("Hello {:&<5}!", "x"), __);

12. println!("Success!");
13. }

5.🌟🌟 You can pad numbers with extra zeros.

1. fn main() {
2. println!("Hello {:5}!", 5); // => Hello     5!
3. println!("Hello {:+}!", 5); // =>  Hello +5!
4. println!("Hello {:05}!", 5); // => Hello 00005!
5. println!("Hello {:05}!", -5); // => Hello -0005!

7. /* Fill in the blank */
8. assert!(format!("{number:0>width$}", number=1, width=6) == __);

10. println!("Success!")
11. ;}

Precision

6.🌟🌟 Floating point precision

2. /* Fill in the blanks */
3. fn main() {
4. let v = 3.1415926;

6. println!("{:.1$}", v, 4); // same as {:.4} => 3.1416

8. assert_eq!(format!("__", v), "3.14");
9. assert_eq!(format!("__", v), "+3.14");
10. assert_eq!(format!("__", v), "3");

12. println!("Success!");
13. }

7.🌟🌟🌟 String length

1. fn main() {
2. let s = "Hello, world!";

4. println!("{0:.5}", s); // => Hello

6. assert_eq!(format!("Hello __!", 3, "abcdefg"), "Hello abc!");

8. println!("Success!");
9. }

Binary, octal, hex

format!(“{}”, foo) -> “3735928559”
format!(“0x{:X}”, foo) -> “0xDEADBEEF”
format!(“0o{:o}”, foo) -> “0o33653337357”

8.🌟🌟

1. fn main() {
2. assert_eq!(format!("__", 27), "0b11011");
3. assert_eq!(format!("__", 27), "0o33");
4. assert_eq!(format!("__", 27), "0x1b");
5. assert_eq!(format!("__", 27), "0x1B");

7. println!("{:x}!", 27); // Hex with no prefix => 1b

9. println!("{:#010b}", 27); // Pad binary with 0, width = 10,  => 0b00011011

11. println!("Success!");
12. }

Capture the environment

9.🌟🌟🌟

1. fn get_person() -> String {
2. String::from("sunface")
3. }

5. fn get_format() -> (usize, usize) {
6. (4, 1)
7. }

9. fn main() {
10. let person = get_person();
11. println!("Hello, {person}!");

13. let (width, precision) = get_format();
14. let scores = [("sunface", 99.12), ("jack", 60.34)];
15. /* Make it print:
16. sunface: 99.1
17. jack: 60.3
18. */
19. for (name, score) in scores {
20. println!("{name}: __");
21. }
22. }

Others

Example

1. fn main() {
2. // Exponent
3. println!("{:2e}", 1000000000); // => 1e9
4. println!("{:2E}", 1000000000); // => 1E9

6. // Pointer address
7. let v= vec![1, 2, 3];
8. println!("{:p}", v.as_ptr()); // => 0x600002324050

10. // Escape
11. println!("Hello {{}}"); // => Hello {}
12. }

You can find the solutions here(under the solutions path), but only use it when you need it :)

16.3. formating