Erasing elements from a vector

Question

I want to clear a element from a vector using the erase method. But the problem here is that the element is not guaranteed to occur only once in the vector. It may be presen

Answer 1

Calling erase will invalidate iterators, you could use:

void erase(std::vector& myNumbers_in, int number_in)
{
    std::vector::iterator iter = myNumbers_in.begin();
    while (iter != myNumbers_in.end())
    {
        if (*iter == number_in)
        {
            iter = myNumbers_in.erase(iter);
        }
        else
        {
           ++iter;
        }
    }

}

Or you could use std::remove_if together with a functor and std::vector::erase:

struct Eraser
{
    Eraser(int number_in) : number_in(number_in) {}
    int number_in;
    bool operator()(int i) const
    {
        return i == number_in;
    }
};

std::vector myNumbers;
myNumbers.erase(std::remove_if(myNumbers.begin(), myNumbers.end(), Eraser(number_in)), myNumbers.end());

Instead of writing your own functor in this case you could use std::remove:

std::vector myNumbers;
myNumbers.erase(std::remove(myNumbers.begin(), myNumbers.end(), number_in), myNumbers.end());

In C++11 you could use a lambda instead of a functor:

std::vector myNumbers;
myNumbers.erase(std::remove_if(myNumbers.begin(), myNumbers.end(), [number_in](int number){ return number == number_in; }), myNumbers.end());

In C++17 std::experimental::erase and std::experimental::erase_if are also available, in C++20 these are (finally) renamed to std::erase and std::erase_if (note: in Visual Studio 2019 you'll need to change your C++ language version to the latest experimental version for support):

std::vector myNumbers;
std::erase_if(myNumbers, Eraser(number_in)); // or use lambda

or:

std::vector myNumbers;
std::erase(myNumbers, number_in);