string 从字符串中取出单个字符
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Getting a single character out of a string
提问by XAMPPRocky
I want to get the first character of a std::str. The method char_at()is currently unstable, as is slice_charsin std::string::String.
我想获得 a 的第一个字符std::str。该方法char_at()目前不稳定，就像slice_chars在std::string::String.
The only option I have currently come up with is the following.
我目前想出的唯一选项如下。
let text = "hello world!";
let char_vec:Vec<char> = text.chars().collect();
let ch = char_vec[0];
But this seems excessive to just get a single character, and not use the rest of the vector.
但这似乎过分了，只得到一个字符，而不使用向量的其余部分。
回答by Steve Klabnik
UTF-8 does not define what "character" is so it depends on what you want. In this case, chars are Unicode scalar values, and so the first charof a &stris going to be between one and four bytes.
UTF-8 没有定义“字符”是什么，所以它取决于你想要什么。在这种情况下，chars 是 Unicode 标量值，因此 a 的第char一个&str将介于 1 到 4 个字节之间。
If you want just the first char, then don't collect into a Vec<char>, just use the iterator:
如果您只想要第一个char，则不要收集到 a 中Vec<char>，只需使用迭代器：
let text = "hello world!";
let ch = text.chars().next().unwrap();
回答by Sean
I wrote a function that returns the head of a &strand the rest:
我写了一个函数，返回 a 的头部&str和其余部分：
fn car_cdr(s: &str) -> (&str, &str) {
for i in 1..5 {
let r = s.get(0..i);
match r {
Some(x) => return (x, &s[i..]),
None => (),
}
}
(&s[0..0], s)
}
Use it like this:
像这样使用它：
let (first_char, remainder) = car_cdr("test");
println!("first char: {}\nremainder: {}", first_char, remainder);
The output looks like:
输出看起来像：
first char: t
remainder: est
It works fine with chars that are more than 1 byte.
它适用于超过 1 个字节的字符。
回答by FeFiFoFu
The accepted answer is a bit ugly!
接受的答案有点难看！
let text = "hello world!";
let ch = &text[0..1]; // this returns "h"
