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| -rw-r--r-- | src/doc/book/vectors.md | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/src/doc/book/vectors.md b/src/doc/book/vectors.md index 7b826f08ae6..b09735c3fee 100644 --- a/src/doc/book/vectors.md +++ b/src/doc/book/vectors.md @@ -61,6 +61,33 @@ error: aborting due to previous error There’s a lot of punctuation in that message, but the core of it makes sense: you cannot index with an `i32`. +## Out-of-bounds Access + +If you try to access an index that doesn’t exist: + +```ignore +let v = vec![1, 2, 3]; +println!("Item 7 is {}", v[7]); +``` + +then the current thread will [panic] with a message like this: + +```text +thread '<main>' panicked at 'index out of bounds: the len is 3 but the index is 7' +``` + +If you want to handle out-of-bounds errors without panicking, you can use +methods like [`get`][get] or [`get_mut`][get_mut] that return `None` when +given an invalid index: + +```rust +let v = vec![1, 2, 3]; +match v.get(7) { + Some(x) => println!("Item 7 is {}", x), + None => println!("Sorry, this vector is too short.") +} +``` + ## Iterating Once you have a vector, you can iterate through its elements with `for`. There @@ -87,3 +114,6 @@ API documentation][vec]. [vec]: ../std/vec/index.html [generic]: generics.html +[panic]: concurrency.html#panics +[get]: http://doc.rust-lang.org/std/vec/struct.Vec.html#method.get +[get_mut]: http://doc.rust-lang.org/std/vec/struct.Vec.html#method.get_mut |