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@TODO: make a general discuss about removing elements form containers ...

vector -> best to remove backwards ...

You cannot erase elements from a container using the function std::for_each or the range-based for loop (introduced in C++11). It is easy to make mistakes while you erases elements using iterator in C++.

the following discussion is for set only

Suppose numbers is a container with integer number, and we want to erase the even numbers from it. The following code is a correct way to do this.

for(auto it=numbers.begin(); it!=numbers.end(); ){
    // copy the current iterator then increase it
    auto cit = it;
    ++it;
    if((*cit) % 2 == 0){
        // won't invalidate iterator it, 
        // because it is already pointing to the next element
        numbers.erase(cit);
    }
}