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Remove elements from a container

1234567891011121314 #include <vector> #include <algorithm> int main() { std::vector<int> v = {1, 2, 3, 4, 2, 5, 2, 6}; v.erase(std::remove(std::begin(v), std::end(v), 2), std::end(v)); v.erase(std::remove_if(std::begin(v), std::end(v), [](int i) { return i%2 == 0; }), std::end(v)); }

This pattern is licensed under the CC0 Public Domain Dedication.

Requires c++11 or newer.

Intent

Use the erase-remove idiom to remove elements from a container.

Description

On line 6, we create a std::vector as an example container and initialize it some int elements.

The std::remove and std::remove_if algorithms do not have knowledge about the underlying storage of the given range, so cannot actually remove elements from that storage. Instead, these algorithms actually shift (by means of move assignment) the elements in the range in such a way that the elements not removed form a new range at the beginning of the original range. The algorithms return a past-the-end iterator for this new range, which, since the removed elements have been shifted to the end of the original range, also marks the start of the removed elements.

On lines 8–9, we show how we can pass the resulting iterator to the container’s erase member function, which actually removes the elements from the container. Similarly, on lines 11–13, we demonstrate how std::remove_if can be used with erase to remove all elements for which a given predicate returns true (in the example code, we remove all even elements).

This technique of using the generic remove algorithms followed by a call to the particular container’s erase member function is commonly referred to as the erase-remove idiom.

Contributors

Last Updated

10 December 2017

Source

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