map::insert vs. map[key] = value: When is one more efficient than the other?

Inserting Values into STL Maps: Efficiency Considerations

In STL maps, both map::insert and map[key] = value can be used to insert key-value pairs. However, the two approaches differ in functionality and efficiency.

map::insert

map::insert is specifically designed for inserting new key-value pairs. It takes a pair of key and value and attempts to insert it into the map. If the key already exists, the insertion fails and the old value is retained.

map[key] = value

On the other hand, map[key] = value acts more like a convenient shortcut. When used to insert a new key-value pair, it automatically checks if the key exists. If it does, the existing value is replaced with the new value. However, if the key does not exist, a new key-value pair is created.

Efficiency

While map[key] = value is often easier to read and use, it is important to note that it can be less efficient than map::insert. This is because map[key] = value performs an additional check to determine if the key exists. This check requires an extra lookup in the map, which can become more noticeable for larger maps.

In contrast, map::insert only performs the insertion operation. It does not need to check if the key exists, as it only inserts the pair if it does not already exist. This can result in improved performance, especially for scenarios where you are primarily inserting new key-value pairs.

Conclusion

The choice between map::insert and map[key] = value depends on the specific requirements of your application. If performance is a concern, or if you need to explicitly handle the case when a key already exists, map::insert is the recommended choice. For scenarios where readability and simplicity are more important, map[key] = value remains a viable option.

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