rust-course/book/writing-material/posts/string.md

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## 字符串常量
```rust
fn main() {
// You can use escapes to write bytes by their hexadecimal values...
let byte_escape = "I'm writing \x52\x75\x73\x74!";
println!("What are you doing\x3F (\\x3F means ?) {}", byte_escape);
// ...or Unicode code points.
let unicode_codepoint = "\u{211D}";
let character_name = "\"DOUBLE-STRUCK CAPITAL R\"";
println!("Unicode character {} (U+211D) is called {}",
unicode_codepoint, character_name );
let long_string = "String literals
can span multiple lines.
The linebreak and indentation here ->\
<- can be escaped too!";
println!("{}", long_string);
}
```
```rust
fn main() {
let raw_str = r"Escapes don't work here: \x3F \u{211D}";
println!("{}", raw_str);
// If you need quotes in a raw string, add a pair of #s
let quotes = r#"And then I said: "There is no escape!""#;
println!("{}", quotes);
// If you need "# in your string, just use more #s in the delimiter.
// There is no limit for the number of #s you can use.
let longer_delimiter = r###"A string with "# in it. And even "##!"###;
println!("{}", longer_delimiter);
}
```
## Bytes string
Want a string that's not UTF-8? (Remember, `str` and `String` must be valid UTF-8). Or maybe you want an array of bytes that's mostly text? Byte strings to the rescue!
```rust
use std::str;
fn main() {
// Note that this is not actually a `&str`
let bytestring: &[u8; 21] = b"this is a byte string";
// Byte arrays don't have the `Display` trait, so printing them is a bit limited
println!("A byte string: {:?}", bytestring);
// Byte strings can have byte escapes...
let escaped = b"\x52\x75\x73\x74 as bytes";
// ...but no unicode escapes
// let escaped = b"\u{211D} is not allowed";
println!("Some escaped bytes: {:?}", escaped);
// Raw byte strings work just like raw strings
let raw_bytestring = br"\u{211D} is not escaped here";
println!("{:?}", raw_bytestring);
// Converting a byte array to `str` can fail
if let Ok(my_str) = str::from_utf8(raw_bytestring) {
println!("And the same as text: '{}'", my_str);
}
let _quotes = br#"You can also use "fancier" formatting, \
like with normal raw strings"#;
// Byte strings don't have to be UTF-8
let shift_jis = b"\x82\xe6\x82\xa8\x82\xb1\x82\xbb"; // "ようこそ" in SHIFT-JIS
// But then they can't always be converted to `str`
match str::from_utf8(shift_jis) {
Ok(my_str) => println!("Conversion successful: '{}'", my_str),
Err(e) => println!("Conversion failed: {:?}", e),
};
}
```