c++ - 在派生类的构造函数中初始化没有默认构造函数的基类

Question

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 primary 类。现在我明白了

no matching function to call

错误。有人可以帮助我吗？

我的代码:
初级.h:

#ifndef PRIMARY_H
#define PRIMARY_H


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

#endif // PRIMARY_H

主要.cpp:

#include "primary.h"

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

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

次级.h:

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


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

#endif // SECONDARY_H

二级.cpp:

#include "secondary.h"

secondary::secondary()
{
    //ctor
}

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

Answer 1

因为您没有默认构造函数，编译器提示它无法为 primary 创建对象，您应该向 secondary 构造函数添加一个参数/给它一个默认值:

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

然后调用基类的构造函数:

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

或者:

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

或者只为 primary 添加一个默认构造函数:

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