Algorithm to convert std::stack to std::string in C++ STL

Question

In below C++ program I'm deleting a previous character considering '#' as a backspace character. I have used stack to build the string. Is there any C++ STL algorithm, which can help me to covert the std::stack to std::string. Any alternative to the code with 'while' loop.

string buildString(string s) {
    stack<char> st;
    for(auto a : s) {
        if(a != '#') {
            st.push(a);
        } 
        else if(st.size()){
            st.pop();
        }
    }

    string result;
    while(st.size()) {
        result += st.top();
        st.pop();
    }

    reverse(begin(result), end(result);

    return result;
}

Answer 1

I'm deleting a previous character considering '#' as a backspace character. I have used stack to build the string.

You could do this without additional space like std::stack:

std::string buildString(const std::string& s) {
  std::string result;
    for(auto a : s) {
        if(a != '#') {
            result += a;
        } 
        else if(result.size()){
            result.pop_back();
        }
    }

    return result;
}