What does the :: mean in C++? [duplicate]

Question

void weight_data::rev_seq(string &seq){ 
//TODO
std::reverse(seq.begin(), seq.end());
}

In this C++ method, I think this method does not return anything, so the prefix is void, what does :: tell the relationships between weight_data and rev_seq(string &seq)? Thanks!

Answer 1

void is the return type. :: is the scope resolution operator, so it means rev_seq is inside the scope of weight_data. weight_data could be either a namespace or a class (based on what you've given, it's not possible to say which).