编译问题：instantiate from here

 

 

/*
 * tempmemb.cpp
 *
 * Created on: 2008-8-26
 * Author: efegliu
 */

#ifndef TEMPMEMB_CPP_
#define TEMPMEMB_CPP_

#include <iostream>

using std::cout;
using std::endl;

template <typename T>
class beta{
private:
    template <typename V>
    class hold{
    private:
        V val;
    public:
        hold(V v=0):val(v){}
        void show()const{ cout << val << endl;}
        V Value()const{return val;}
    };
    hold<T> q;
    hold<int> n;
public:
    beta(T t, int i) : q(t), n(i) {}
    template<typename U>
    U blab(U u, T t){ return (n.Value() + q.Value()) * u / t;}
    void Show() const {q.show(); n.show();}
};

int main(){
    beta<double> guy(3.5, 3);
    guy.Show();
    cout << guy.blab(10, 2.3) << endl;
    cout << "Done\n";
    system("PAUSE");
    return 0;
}

#endif /* TEMPMEMB_CPP_ */


 

编译的时候出错：

 

[support@ailf ~]$ g++ tempmemb.cpp -o tempmemb tempmemb.cpp: In member function `U beta::blab(U, T) [with U = int, T = double]': tempmemb.cpp:33: instantiated from here tempmemb.cpp:25: warning: converting to `int' from `double'

 

查找错误原因：

一.

 

template removed,

problem solved:

Summary: "instantiate from here" = "please remove template"

I don't want to sound sarcastic, but today (2008) a compiler that is responsible for so many applications should know how to handle templates .. and should be able to report errors with enough data.