How to define external struct in a class constructor in c ?-CodePudding

I'm trying to initialize a struct object defined in an external header file inside a class constructor. The problem is I need to include the header file inside the class header file myClass.h, which is causing already defined error I have tried to encapsulate the #include structHeader.h inside #ifndef #endif and that worked but for some reason, It stopped working after some other changes.

The struct works well inside myClass.cpp but I have to initialize it outside the class, which means it will belong to the class and not to an instance of the class. Of course, I will have to include the struct header file in myClass.cpp instead of myClass.h even though I'm including the myClass.h inside myClass.cpp in this case.

I couldn't find any examples with this case, I would appreciate any help.

// myStruct.h

#pragma once

#ifndef H
#define H
#define NUM 10

typedef struct SUB
{
    int exmaple;
    int num;
} sub;


typedef struct Circle
{
    float circleC;
    float circlePoints[NUM];
} Circle;

#endif

// myClass.h

#include "myStruct.h"

class MYCLASS{
  private: 
     Sub subObject;
     Circle circleObject;
     
    OTHERCLASS otherInstance;
    int someValue;

  public: 
     MYCLASS::MYCLASS(int someValue);
     void someFunction();

//  myClass.cpp

#include "myClass.h"
#include "otherClass.h"

MYCLASS::MYCLASS(int someValue, OTHERCLASS otherInstance){
   this->someValue = someValue;
   this->otherInstance = otherInstance;
   // DO I need to initialize struct here?
}

MYCLASS::someFunction(){
}

// main.cpp

#include "myClass.h"
#include "otherClass.cpp"

int main(int argc, char* argv[]){
  MYCLASS instance(2, OTHERCLASS());
  return 0;  
{

This is a sample of what I want to do, also if you could tell me how to add an instance of an external class in myClass constructor instead of passing the instance as a constructor parameter would be great I have tried many things but still getting some errors.

CodePudding user response：

Since as you stated your class will not be the owner of the struct but just needs to have a reference to it a forward declaration of the external struct in your header file is enough. (https://www.learncpp.com/cpp-tutorial/forward-declarations/) If you would need implementation details in your header file you can use the pimpl pattern : https://en.cppreference.com/w/cpp/language/pimpl

#include <iostream>

// myclass.h
//-----------------------------------------------------------------------------
// 
// do NOT include "external_struct.h" but add a forward declaration to the struct.
struct external_struct;

class MyClass final
{
public:
    explicit MyClass(const external_struct& s);
    void f();

private:
    const external_struct& m_struct;
};

// myclass.cpp
//-----------------------------------------------------------------------------
// #include "external_struct.h"
struct external_struct
{
    int x = 0;
    int y = 0;
};

MyClass::MyClass(const external_struct& s) :
    m_struct{ s }
{
}

void MyClass::f()
{
    std::cout << m_struct.x << "\n";
    std::cout << m_struct.y << "\n";
}

//-----------------------------------------------------------------------------
// #include "myclass.h"
int main()
{
    external_struct s;
    MyClass o{ s };
    o.f();
}

CodePudding user response：

Take it easy, I modified part of the code and now the code can run, I uploaded the modified code, please compare carefully.

// myClass.h
#include "myStruct.h"
#include"otherClass.h"
class MYCLASS {

    SUB subObject;
    Circle circleObject;

    OTHERCLASS otherInstance;
    int someValue;

public:
    MYCLASS(int someValue, OTHERCLASS otherInstance);
    void someFunction();

};

// otherClass.h
#pragma once
typedef struct OTHERCLASS
{

} other;

//  myClass.cpp

#include "myClass.h"
#include "otherClass.h"

MYCLASS::MYCLASS(int someValue, OTHERCLASS otherInstance) {
    this->someValue = someValue;
    this->otherInstance = otherInstance;
    // DO I need to initialize struct here?
}
void MYCLASS::someFunction()
{
    
}


// main.cpp
#include "myClass.h"
#include "otherClass.h"

int main(int argc, char* argv[]) {
    MYCLASS instance(2, OTHERCLASS());
    return 0;
}