在基 class 中使用派生 class，而派生 class 在基 class 之后声明

Question

我有头文件

#ifndef CATEGORY_H
#define CATEGORY_H

#include <functional>
#include <string>
#include <vector>

class Category
{
    private:
        std::string nameCategory;
        std::vector<Rule> setOfRules;
    protected:
    public:
        Category();
        Category(std::string nameCategory);
        void setIndexBankAccountEntry(unsigned int iBankAccountEntry);
};

class Rule : public Category
{
    private:
        std::function<void(int)> rule;
    protected:
    public:
        Rule();
        Rule(std::function<void(int)> rule);
};
#endif

其中命令 std::vector<Rule> setOfRules; 给出了 Rule 尚未声明的错误。

交换两个类的声明顺序得到

#ifndef CATEGORY_H
#define CATEGORY_H

#include <functional>
#include <string>
#include <vector>

class Rule : public Category
{
    private:
        std::function<void(int)> rule;
    protected:
    public:
        Rule();
        Rule(std::function<void(int)> rule);
};

class Category
{
    private:
        std::string nameCategory;
        std::vector<Rule> setOfRules;
    protected:
    public:
        Category();
        Category(std::string nameCategory);
        void setIndexBankAccountEntry(unsigned int iBankAccountEntry);
};
#endif

但随后我收到 expected class-name before ‘{’ token 行 class Rule : public Category.

的错误

我该如何解决这个问题？

Answer 1

您可以转发声明class规则：

#ifndef CATEGORY_H
#define CATEGORY_H

#include <functional>
#include <string>
#include <vector>

class Rule; // <-- here

class Category
{
    private:
        std::string nameCategory;
        std::vector<Rule> setOfRules;
    protected:
    public:
        Category();
        Category(std::string nameCategory);
        void setIndexBankAccountEntry(unsigned int iBankAccountEntry);
};

class Rule : public Category
{
    private:
        std::function<void(int)> rule;
    protected:
    public:
        Rule();
        Rule(std::function<void(int)> rule);
};
#endif

Answer 2

您可以为 class Rule 使用前向声明（基于第一个示例）。

class Rule;
class Category
{
    private:
        std::string nameCategory;
        std::vector<Rule> setOfRules;
    protected:
    public:
        Category();
        Category(std::string nameCategory);
        void setIndexBankAccountEntry(unsigned int iBankAccountEntry);
};
// class Rule definition here

勾选here

在基 class 中使用派生 class，而派生 class 在基 class 之后声明

Use derived class in base class while derived class is declared after the base class

c++

derived-class