How to check if a string contains a substring in Rust?

Question

I'm trying to find whether a substring is in a string. In Python, this involves the in operator, so I wrote this code:

let a = "abcd";
if "bc" in a {
    do_something();
}

I get a strange error message:

error: expected `{`, found `in`
 --> src/main.rs:3:13
  |
3 |       if "bc" in a {
  |  _____________-^
4 | |         do_something();
5 | |     }
  | |_____- help: try placing this code inside a block: `{ a <- { do_something(); }; }`

The message suggests that I put it in a block, but I have no idea how to do that.

Shepmaster · Accepted Answer · 2018-02-14 20:12:15Z

178

Rust has no such operator. You can use the String::contains method instead:

if a.contains("bc") {
    do_something();
}

edited Feb 14, 2018 at 20:12

Shepmaster

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answered Feb 14, 2018 at 19:57

Kevin Hoerr

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5 Comments

g.delgado Over a year ago

What if I want to see if a string contains, say, one more more capital letters?

Kevin Hoerr Over a year ago

You should probably post that as a separate question. Personally, I'd try to use regex for that.

David Over a year ago

For anyone else who comes to this. you can do thing.contains(['A', 'B', 'C]) to check if thing has capitalized A, B, or C in it.

ihsan Over a year ago

how do i also get the index?

Kevin Hoerr Over a year ago

If you check the docs, there is a String::find method that returns the index for characters or fuller string patterns

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