c++ - '&' token 错误之前的预期构造函数，析构函数或类型转换

我的文件:

cpu_add.h

#ifndef CPU_ADD_H
#define CPU_ADD_H

double add_double_double(double a, double b) {return (a+b);}
double add_int_double(int a, double b) {return ((double)(a)+b);}
int   add_int_int(int a, int b) {return (a+b);}

#endif

只允许使用上述功能。无法在我自己的代码中使用运算符“+”。

poly_subtype.h

#ifndef POLY_SUBTYPE_H
#define POLY_SUBTYPE_H
#include <iostream>
#include "q3.h"
#include "cpu_add.h"
using std::cout;
using std::endl;

//Deriving classes definition
class IntClass;
class DoubleClass;

//The Virtual Number Class. IntClass and FloatClass will derive from this class.
class Number {
    public:
        //return a Number object that's the results of x+this, when x is DoubleClass
        virtual Number& addDouble(DoubleClass& x) = 0;

        //return a Number object that's the results of x+this, when x is IntClass
        virtual Number& addInt(IntClass& x) = 0;

        //return a Number object that's the results of x+this, when x is either
        //IntClass or DoubleClass
        virtual Number& operator+(Number& x) = 0;

        //Print the number stored in the object
        virtual void print_number() = 0;
};

class IntClass : public Number {
    private:
        int my_number;
    public:
        //Constructor
        IntClass(int n):my_number(n) {}

        //returns the number stored in the object
        int get_number()  {return my_number;}

        //print the number stored in the object
        void print_number() {cout << my_number << endl;}

        //return a DoubleClass object that's the result of x+this
        Number& addDouble(DoubleClass& x);

        //return an IntClass object that's the result of x+this
        Number& addInt(IntClass& x);

        //return a Number object that's the result of x+this.
        //The actual class of the returned object depends on x.
        //If x is IntClass, then the result if IntClass.
        //If x is DoubleClass, then the results is DoubleClass.
        Number& operator+(Number& x);
};

class DoubleClass : public Number {
    private:
        double my_number;
    public:
        //Constructor
        DoubleClass(double n):my_number(n) {}

        //returns the number stored in the object
        double get_number()  {return my_number;}

        //Print the number stored in the object
        void print_number() {cout << my_number << endl;}

        //return a DoubleClass object that's the result of x+this
        Number& addDouble(DoubleClass& x);

        //return a DoubleClass object that's the result of x+this
        Number& addInt(IntClass& x);

        //return a DoubleClass object that's the result of x+this.
        //This should work if x is either IntClass or DoubleClass
        Number& operator+( Number& x);
};

#endif

我需要实现以下功能:

Number& IntClass::addInt(IntClass& x);
Number& IntClass::addDouble(DoubleClass& x);
Number& IntClass::operator+(Number& x);
Number& DoubleClass::addInt(IntClass& x);
Number& DoubleClass::addDouble(DoubleClass& x);
Number& DoubleClass::operator+(Number& x);

例如，在我的q3.h中，我写道:

#ifndef Q3_H_
#define Q3_H_

#include "cpu_add.h"
#include "poly_subtype.h"

Number& IntClass::addInt(IntClass& x){
    IntClass num(add_int_int(my_number, x.get_number()));
    return num;
}
#endif /* Q3_H_ */

我得到下一个错误:

expected constructor, destructor, or type conversion before '&' token   q3.h    ‪/pl5‬  line 48 C/C++ Problem

这是什么意思？

谢谢。

最佳答案

这是因为您将所有代码放在 header 中(可能是Java的方式？)。

当您包含poly_subtype.h时，它包含q3.h，然后包含poly_subtype.h试图定义各种类。由于您的包含防护，第二个包含无效。然后，当编译器尝试编译q3.h时，它不知道Number类是什么，并生成该错误。

解决此问题的方法是将您的方法实现放入仅编译一次的源文件中。它将防止嵌套包含问题。或者，我完全看不到poly_subtype.h为什么需要包含q3.h。如果删除该包含，它可能会解决。

另外请注意，IntClass::addInt通过引用返回一个本地，尽管它似乎可以正常工作，但这绝对是不正确的。您应该改为return *this;，它是被修改的实际对象(我相信-很难从您的小样本中看出)。