Why Does `at()` Work with Const Maps While `operator[]` Fails?

Understanding Operator[] and at() for Const Maps

When working with const maps in C , accessing elements using the operator[] might encounter issues. In the provided example, it fails, while using the at() function succeeds. This article will delve into the reasons and provide further information about at().

In a const std::map, the operator[] cannot access elements directly because it attempts to modify the map, which is against the const restriction. However, the at() function, introduced in C 11, is designed to handle read-only access. Instead of inserting a default-constructed element like operator[], at() throws a std::out_of_range exception if an element with the given key does not exist.

This exception handling behavior makes at() suitable for use with const maps, as it guarantees element access without causing unintended map modifications. Unlike operator[], which always has the potential to change the map, at() offers a safe and convenient way to retrieve element values from a const std::map.

For further reference, documentation on at() can be found in the C Reference: https://en.cppreference.com/w/cpp/container/map/at.

The above is the detailed content of Why Does `at()` Work with Const Maps While `operator[]` Fails?. For more information, please follow other related articles on the PHP Chinese website!