在派生类的构造函数中初始化没有默认构造函数的基类 [英] Initialize base class with no default constructor in constructor of derived class

问题描述

我正在尝试创建一个子类 secondary ，它可以与参数一起使用，也可以覆盖类 primary 。现在我得到

I'm trying to create a subclass secondary which could be used with a parameter as well as it's overriding class primary. Now I get

没有匹配的函数可以调用

no matching function to call

错误。有人可以帮帮我吗？

error. Could someone help me?

我的代码：

primary.h：

My code:
primary.h:

#ifndef PRIMARY_H
#define PRIMARY_H


class primary
{
    public:
        primary(int x);
        virtual ~primary();
    protected:
    private:
        int primary_x;
};

#endif // PRIMARY_H

primary.cpp：

primary.cpp:

#include "primary.h"

primary::primary(int x)
{
    primary_x = x;
}

primary::~primary()
{
    //dtor
}

secondary.h：

secondary.h:

#ifndef SECONDARY_H
#define SECONDARY_H
#include "primary.h"


class secondary : public primary
{
    public:
        secondary();
        virtual ~secondary();
    protected:
    private:
};

#endif // SECONDARY_H

secondary.cpp：

secondary.cpp:

#include "secondary.h"

secondary::secondary()
{
    //ctor
}

secondary::~secondary()
{
    //dtor
}

推荐答案

因为您没有默认构造函数，编译器会抱怨它无法创建对象 primary ，你应该在 secondary 构造函数中添加一个参数/给它一个默认值：

Because you don't have a default constructor the compiler complains that it can't create an object for primary, you should either add a parameter to the secondary constructor / give it a default value:

class secondary : public primary
{
    public:
        secondary(int x);
        virtual ~secondary();
    protected:
    private:
};

然后调用基类构造函数：

And then call the base class constructor:

secondary::secondary(int x) : primary(x)
{
    //ctor
}

或者：

secondary::secondary() : primary(5)
{
    //ctor
}

或者只为主要添加默认构造函数：

Or just add a default constructor for primary:

class primary
{
    public:
        primary(int x);
        primary() : primary_x(0) {}
        virtual ~primary();
    protected:
    private:
        int primary_x;
};

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