Question

A simple c++ file and the class TT has two methods.

#include <map>
#include <string>
#include <iostream>

using namespace std;

class TT{ 
    public:
        TT(const string& str);
        template<class T>T Read(const string& key)const;
        template<class T>T Read(const string& key, const T& value)const;
};

TT::TT(const string& str){
    cout<<str<<endl;
}

template<class T>T TT::Read(const string& key)const{
    std::cout<<key<<std::endl;
    return 1;
}

template<class T>T TT::Read(const string& key, const T& value)const{
    std::cout<<key<<'\t'<<value<<std::endl;
    return value;
}

int main(void){
    TT tt("First");

    tt.Read("Hello", 12);
    return 1;
}

If replace the

tt.Read("Hello world!", 12);

with

tt.Read("Hello world!");

in main()

G++ says:

new.cc:31: error: no matching function for call to ‘TT::Read(const char [5])’

Why G++ cann’t find the Read(const string& key)const method?

Thanks!

Answer 1

You’re trying to define a function that returns a T:

template<class T>
T TT::Read(const string& key) const
{
    std::cout << key << std::endl;
    return 1;
}

However, you always return an int from this function. You either need to call it like so:

tt.Read<int>("Hello");

Or remove the template definition, as it makes no sense here.