从父类定义调用学生方法

在声明类方法之前,不能使用它。

使用正向声明是解决类之间循环引用问题的正确方法。那么你为 lcdmenu::submenulist 成员(可能也适用于 lcdmenu::commandlist 成员)完全可以声明 lcdmenu 班

但是,前瞻性声明无助于 lcdmenu::render() 方法它需要的完整声明 submenu 类,以便访问其成员,例如 submenu::get_text() 方法(与相同 command 班

因此,您需要将声明和实现拆分为单独的 .h 和 .cpp 帮助完成此任务的文件,例如:

lcdmenu。h

#ifndef lcdmenu_H
#define lcdmenu_H

class command;
class submenu;

class lcdmenu
{
protected:
    command **commandlist;
    submenu **submenulist;
    ...   

public:
    void setchildren(command **comlist, submenu **sublist, int comn, int subn);
    void render();
    ...
};

#endif

lcdmenu.cpp

#include "lcdmenu.h"
#include "submenu.h"
#include "command.h"
...

void lcdmenu::render(){
    lcd_clear();
    for (int line = 0; line < MAX_LINES; line ++){
        int index = menutop + line;
        ...

        if (index < numcommands){
            lcd_string(commandlist[index]->get_text());
            lcd_string(submenulist[index]->get_text()); 
        }

子菜单。h

#ifndef submenu_H
#define submenu_H

#include "lcdmenu.h"

class submenu : public lcdmenu {
public:
    lcdmenu *parent;
    submenu(lcdmenu *par, const char* text);

    const char* get_text();
};

#endif

submenu.cpp

#include "submenu.h"

submenu::submenu(lcdmenu *par, const char* text_):text(text_), parent(par)
{
}

const char* submenu::get_text(){
    return text;
}

命令h

#ifndef command_H
#define command_H

...

class command ... {
public:
    ...
    const char* get_text();
};

#endif

命令.cpp

#include "command.h"

...

const char* command::get_text(){
    return ...;
}

现在,当您编译 lcdmenu.cpp ,编译器将在预处理器替换后看到以下代码:

class command;
class submenu;

class lcdmenu
{
protected:
    command **commandlist;
    submenu **submenulist;
    ...   

public:
    void setchildren(command **comlist, submenu **sublist, int comn, int subn);
    void render();
    ...
};

class submenu : public lcdmenu {
public:
    lcdmenu *parent;
    submenu(lcdmenu *par, const char* text);

    const char* get_text();
};

...
class command ... {
public:
    ...
    const char* get_text();
};

...

void lcdmenu::render(){
    lcd_clear();
    for (int line = 0; line < MAX_LINES; line ++){
        int index = menutop + line;
        ...

        if (index < numcommands){
            lcd_string(commandlist[index]->get_text());
            lcd_string(submenulist[index]->get_text()); 
        }

当你编译 submenu.cpp ,编译器将在预处理器替换后看到以下代码:

class command;
class submenu;

class lcdmenu
{
protected:
    command **commandlist;
    submenu **submenulist;
    ...   

public:
    void setchildren(command **comlist, submenu **sublist, int comn, int subn);
    void render();
    ...
};

class submenu : public lcdmenu {
public:
    lcdmenu *parent;
    submenu(lcdmenu *par, const char* text);

    const char* get_text();
};

submenu::submenu(lcdmenu *par, const char* text_):text(text_), parent(par)
{
}

const char* submenu::get_text(){
    return text;
}

当你编译 command.cpp ,编译器将在预处理器替换后看到以下代码:

...

class command ... {
public:
    ...
    const char* get_text();
};

...

const char* command::get_text(){
    return ...;
}