如何从向量中删除第一次出现的值？

Question

I'm trying to get a single element from a vector and push it to the back of the vector then remove it so I won't have an empty section in memory. The erase-remove idiom can do this but it removes all instances of a particular value. I just want the first one removed.

I'm not too experienced with standard library algorithms and I can't find the appropriate methods (if any) to do this. Here is an example:

int main() {
    std::vector<int> v{1, 2, 3, 3, 4};

    remove_first(v, 3);

    std::cout << v; // 1, 2, 3, 4
}

So how would I go about removing the first occurance of a 3 from this vector?

Answer 1

Find it first, then erase it:

auto it = std::find(v.begin(),v.end(),3);
// check that there actually is a 3 in our vector
if (it != v.end()) {
  v.erase(it);
}

Answer 2

If you don't care about maintaining the ordering of the elements in the vector, you can avoid the copy of the "tail" of remaining elements on erase:

auto it = std::find(v.begin(), v.end(), 3);
if (it != v.end()) {
  std::iter_swap(it, v.end() - 1);
  v.erase(v.end() - 1);
}