Question

I haven’t used the STL much before, but I started to on this huffman compression project. Everything seems to work except the “for_each” function, which wont except a function argument. Since I don’t normally use xcode (I usually use eclipse cdt) I’m not sure if the problem is with my code or with xcode.

This is the Huff.h file

class Huff {
private:
    typedef pair<char, int> c_pair;
    vector<Node> nodes;
    vector<Code> code;
    string content;
    void copy_to(c_pair c);
public:
    Huff(string);
    ~Huff();

    string compress();
    bool set_content();
    string get_content();
    string get_compress();
};

And this is the part of the Huff.cpp file that will not work.

//---Compress---

void Huff::copy_to(c_pair c){
    Node n(c.second, c.first, NULL, NULL);
    nodes.push_back(n);
}
string Huff::compress(){
    map<char, int> freq;
    for(int i = 0; i < content.length(); i++)
        freq[content[i]]++;
    for_each(freq.begin(), freq.end(), copy_to); //I've also tried this->copy_to
    return "110";
}

Answer 1

for_each(freq.begin(), freq.end(), copy_to); //I've also tried this->copy_to

copy_to is a member function which cannot be passed to std::for_each.

What you need is a callable entity which doesn’t need implicit this : such an entity can be either functor or free function, and in C++11, lambda also.

The lambda solution would be pretty simple if you can use it:

for_each(freq.begin(), 
         freq.end(), 
         [this](c_pair & c) { this->copy_to(c); } ); 

Learn about lambda expression here:

• What is a lambda expression in C++11?