How Do I Efficiently Remove Elements by Value from an STL Vector?

Erasing Elements from an STL Vector by Value

When working with STL vectors, removing an element by its value may appear to be a basic operation, yet there seems to be no straightforward method within the vector class itself.

The std::remove function provides a solution for this common task. However, it's important to note that std::remove does not directly remove elements from the container. Instead, it repositions elements that satisfy a given condition to the beginning of the container. To complete the removal process, this modified container must be passed to container_type::erase to remove the redundant elements now located at the end.

Consider the following example:

std::vector<int> vec;
// .. populate vec ..
int int_to_remove = n;
vec.erase(std::remove(vec.begin(), vec.end(), int_to_remove), vec.end());

In this example, std::remove repositions all elements not equal to int_to_remove to the beginning of the vector, and returns an iterator pointing to the first element after these elements. This iterator is then used as the argument to std::erase(), effectively removing the remaining elements at the end of the vector.

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