字符串

Rust 中最常用的两种字符串类型是 String 和 &str。

String 类型存储为字节向量 (Vec<u8>)，但保证始终是有效的 UTF-8 序列。 String 类型是堆分配的，可增长的，并且不是以空字符结尾的。

&str 是一个切片 (&[u8])，它总是指向一个有效的 UTF-8 序列，并且可以用来查看 String 的内容，就像 &[T] 是 Vec<T> 的视图一样。

fn main() {
    // (all the type annotations are superfluous)
    // A reference to a string allocated in read only memory
    let pangram: &'static str = "the quick brown fox jumps over the lazy dog";
    println!("Pangram: {}", pangram);

    // Iterate over words in reverse, no new string is allocated
    println!("Words in reverse");
    for word in pangram.split_whitespace().rev() {
        println!("> {}", word);
    }

    // Copy chars into a vector, sort and remove duplicates
    let mut chars: Vec<char> = pangram.chars().collect();
    chars.sort();
    chars.dedup();

    // Create an empty and growable `String`
    let mut string = String::new();
    for c in chars {
        // Insert a char at the end of string
        string.push(c);
        // Insert a string at the end of string
        string.push_str(", ");
    }

    // The trimmed string is a slice to the original string, hence no new
    // allocation is performed
    let chars_to_trim: &[char] = &[' ', ','];
    let trimmed_str: &str = string.trim_matches(chars_to_trim);
    println!("Used characters: {}", trimmed_str);

    // Heap allocate a string
    let alice = String::from("I like dogs");
    // Allocate new memory and store the modified string there
    let bob: String = alice.replace("dog", "cat");

    println!("Alice says: {}", alice);
    println!("Bob says: {}", bob);
}

更多 str/String 方法可以在 std::str 和 std::string 模块下找到。

字面量和转义

有多种方法可以编写包含特殊字符的字符串字面量。所有方法都会产生类似的 &str，因此最好使用最方便编写的形式。类似地，也有多种方法可以编写字节字符串字面量，所有方法都会产生 &[u8; N]。

通常，特殊字符使用反斜杠字符 \ 进行转义。这样，您就可以在字符串中添加任何字符，即使是不可打印的字符以及您不知道如何键入的字符。如果您想要一个文字反斜杠，请使用另一个反斜杠对其进行转义：\\。

出现在字面量中的字符串或字符字面量分隔符必须进行转义："\""、'\''。

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);
}

有时需要转义的字符太多，或者直接按原样编写字符串要方便得多。这就是原始字符串字面量的用武之地。

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.
    // You can use up to 65535 #s.
    let longer_delimiter = r###"A string with "# in it. And even "##!"###;
    println!("{}", longer_delimiter);
}

想要一个不是 UTF-8 的字符串？（请记住，str 和 String 必须是有效的 UTF-8）。或者，您可能想要一个主要由文本组成的字节数组？字节字符串来拯救您！

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),
    };
}

有关字符编码之间转换的信息，请查看 encoding crate。

有关编写字符串字面量和转义字符的方法的更详细列表，请参阅 Rust 参考手册的 “标记”一章。