有人可以解释一下我做错了什么吗?这是我从编译器得到的错误。
非常感谢
1>------ Build started: Project: Ch16, Configuration: Release Win32 ------
1> p643_inclusion.cpp
1> p643_inclusion_main.cpp
1> p643_print.cpp
1>p643_print.cpp(5): error C2065: 'T1' : undeclared identifier
1>p643_print.cpp(5): error C2065: 'T2' : undeclared identifier
1>p643_print.cpp(6): warning C4552: '<<' : operator has no effect; expected operator with side-effect
1>p643_print.cpp(7): warning C4552: '<<' : operator has no effect; expected operator with side-effect
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
p643_inclusion.h
#ifndef P643H
#define P643H
template< class T1, class T2> class Car {
friend void print (const Car<T1, T2> &c1);
private:
T1 Wheels;
T2 DriversName;
public:
Car(): Wheels(4), DriversName("None") {}
Car(T1, T2);
};
template <class T1, class T2> class Driver {
private:
T1 Name;
T2 Surname;
public:
Driver(): Name("None"), Surname("None") {}
};
#include "p643_inclusion.cpp"
#endif
p643_inclusion.cpp
# ifndef P643CC
#define P643CC
#include <iostream>
#include <string>
using std::string;
using std::cout;
using std::endl;
#include "p643_inclusion.h"
template<class T1, class T2>
Car<T1, T2>::Car(T1 w, T2 d) {
Wheels = w;
DriversName = d;
}
#endif
p643_print.cpp
#include "p643_inclusion.h"
template< class T1, class T2> class Car;
void print (const Car<T1, T2> &c1) {
cout << c1.Wheels << endl;
cout << c1.DriversName << endl;
}
主要内容
#include "p643_inclusion.h"
#include<iostream>
#include<string>
using namespace std;
int main()
{
Car<int, string> myCar;
Driver<string, string> myDriver;
print(myCar);
return 0;
}
最佳答案
您的函数实际上并不是非模板函数。
void print (const Car<T1, T2> &c1) {
cout << c1.Wheels << endl;
cout << c1.DriversName << endl;
}
这是错误的。您能问问自己 T1
到底是什么吗?和T2
?
您应该将其实现为:
template<class T1, class T2>
void print (const Car<T1, T2> &c1) {
cout << c1.Wheels << endl;
cout << c1.DriversName << endl;
}
您应该将其设为 friend
:
template< class T1, class T2> class Car {
//choose different name for type params, because enclosing class
//already using T1, and T2
template<class U, class V>
friend void print (const Car<U, V> &c1);
//...
关于c++ - 模板类的非模板函数友元,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/5554844/