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@@ -57,18 +57,26 @@ Strong exception safety: if an exception occurs, the original value stays intact
## Exceptions
1. The function can throw the following exceptions:
- Throws [`type_error.305`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error305) if the JSON value is not an array or null; in that case, using the `[]` operator with an index makes no sense.
- Throws `std::length_error` if `idx` equals the maximum value of `size_type`; the array is left unchanged. (This is the one index for which growing the array to hold it cannot be expressed as a `size_type` size, the same way an oversized [`resize`](https://en.cppreference.com/w/cpp/container/vector/resize) throws.)
1. The function can throw the following exceptions:
- Throws [`type_error.305`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error305) if the JSON value is not an object or null; in that case, using the `[]` operator with a key makes no sense.
1. See 2.
1. The function can throw the following exceptions:
- Throws [`parse_error.106`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error106) if an array index in the passed JSON pointer `ptr` begins with '0'.
- Throws [`parse_error.109`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error109) if an array index in the passed JSON pointer `ptr` is not a number.
- Throws [`out_of_range.402`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range402) if the array index '-' is used in the passed JSON pointer `ptr` for the const version.
- Throws [`out_of_range.404`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range404) if the JSON pointer `ptr` can not be resolved.
- Throws [`out_of_range.410`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range410) if an array index in the passed JSON pointer `ptr` exceeds the range of `size_type` (e.g., on 32-bit platforms).
For the **const** version, an object key or array index in `ptr` that does not exist is not reported by an exception, but is undefined behavior (see the notes below). Use [`at`](https://json.nlohmann.me/api/basic_json/at/index.md) for checked access.
## Complexity
1. Constant if `idx` is in the range of the array. Otherwise, linear in `idx - size()`.
@@ -82,10 +90,12 @@ Undefined behavior and runtime assertions
The following cases apply to the **const** overloads; the non-const overloads instead insert the missing element (see the notes below).
1. If the element at index `idx` does not exist, the behavior is undefined.
1. If the element at index `idx` does not exist, the behavior is undefined and is **guarded by a [runtime assertion](https://json.nlohmann.me/features/assertions/index.md)**!
1. If the element with key `key` does not exist, the behavior is undefined and is **guarded by a [runtime assertion](https://json.nlohmann.me/features/assertions/index.md)**!
1. If the JSON pointer `ptr` refers to an object key or an array index that does not exist, the behavior is undefined and is **guarded by a [runtime assertion](https://json.nlohmann.me/features/assertions/index.md)**!
1. The non-const version may add values: If `idx` is beyond the range of the array (i.e., `idx >= size()`), then the array is silently filled up with `null` values to make `idx` a valid reference to the last stored element. In case the value was `null` before, it is converted to an array.
1. If `key` is not found in the object, then it is silently added to the object and filled with a `null` value to make `key` a valid reference. In case the value was `null` before, it is converted to an object.
@@ -487,7 +497,7 @@ Output:
## Version history
1. Added in version 1.0.0. Fixed in version 3.13.0 unreleased to throw `std::length_error` instead of emptying the array and accessing it out of bounds when `idx` equals the maximum value of `size_type`.
1. Added in version 1.0.0. Fixed in version 3.13.0 unreleased to throw `std::length_error` instead of emptying the array and accessing it out of bounds when `idx` equals the maximum value of `size_type`. A missing index in the const version is guarded by a runtime assertion since version 3.13.0 unreleased.
1. Added in version 1.0.0. Added overloads for `T* key` in version 1.1.0. Removed overloads for `T* key` (replaced by 3) in version 3.11.0.
1. Added in version 3.11.0. Fixed in version 3.13.0 unreleased to consistently accept `std::string_view`-convertible keys, as already supported by [`at`](https://json.nlohmann.me/api/basic_json/at/index.md), [`value`](https://json.nlohmann.me/api/basic_json/value/index.md), [`find`](https://json.nlohmann.me/api/basic_json/find/index.md), and other lookup functions.
1. Added in version 2.0.0.
1. Added in version 2.0.0. A missing array index in the const version is guarded by a runtime assertion since version 3.13.0 unreleased.