How to initialize class with pointer to class

[Q139]

How to initialize class with pointer to class where object to is located;

For example Inside class A is created class B object, now class A can com to class B via object but for class B to com to class A would it be possible to initialize class with pointer or there are better solutions?

´´´
class FileCOM : public QObject
{

public:
FileCOM(TCP_Socketptr); <<<------ this attempt fails and compiler returns : error: expected ')' before '' token

void set_file_location();
void read_file_to_buffer();
void process_buffer();
void write_file(QByteArray data);
std::vector <QByteArray> read_buffer;

};
´´´

[mrjj]

just create a constructor that accepts such pointer ?

class FileCOM : public QObject
{
TCP_Socket *mykeptpointer;
public:
FileCOM(TCP_Socket * theptr) : mykeptpointer(theptr) {}
...
or do i misunderstand you ?

[Q139]

Compiler returns this error msg : error: expected ')' before ' * ' token

[mrjj]

@mrjj said:

are u sure it knows TCP_Socket ?

you did include the .h file where it lives ?

[Q139]

Yes included , problem was due to double include in 2 files.
Is it possible to include file only for .h inside use so when other files include same .h part of files would not be double included?

[mrjj]

This post is deleted!

[mrjj]

@Q139
it is normal to include .h many times.

Are you using guards ?

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#endif

[Q139]

For example when include file1.h in file2.h and file2.h in file1.h compiler returns error: expected ')' before '' token FileCOM(TCP_SocketSOCKETptr); or mostly error: 'FileCOM' does not name a type

For pointer of class A in class B it need include class A .h in B .h file, but for class A to create object of B in .h file it need include of B .h file

[mrjj]

@Q139

Ah, that is called circular include and often solved by using type forwards.
https://en.wikipedia.org/wiki/Circular_dependency

like
in your case
class TCP_Socket; //forward declaration

class FileCOM : public QObject
{
TCP_Socket *mykeptpointer;
....

and then DONT include its .h file

[Q139]

Then it is not possible to declare class FileCOM in .h file of TCP_Socket only .cpp file
Thanks for your time and help, problem is there are multiple instances of sockets and each one should have fileCOM

[mrjj]

@Q139
well you should never have data in the .h file.

but you can using external;
in .h
extern TCP_Socket * TheOnlyInstance;

and in .cpp
TCP_Socket * TheOnlyInstance;

[Q139]

Thanks , will read materials on circular dependency as have had many problem with this.

[mrjj]

@Q139
well we all have :)

Well in your case:
using external.

then in mainwindow, u include TCP_Socket.H

then you have the instance to give to the other objects when you create them

[mrjj]

@Q139 said:

there are multiple instances of sockets and each one should have fileCOM

the same file com?

[Q139]

Yes same class but different filenames.
Foward declaration is good solution and compiles , if it work good , appears to be complex solution for easy problem.

.h file

class TCP_Socket;

class FileCOM : public QObject
{
public:
TCP_Socket * SOCKETptr;
FileCOM(TCP_Socket * ptr){
SOCKETptr=ptr;
}

.h file

class TCP_Socket : public QObject
{
public:
FileCOM * FILE;

.cpp file

void TCP_Server_File::NewConnection()
{
TCP_Socket *soc = new TCP_Socket;
soc->FILE = new FileCOM(soc); <--- if working then here it should pointer of TCP_Socket class to FileCOM class.
soc->New_socket (server->nextPendingConnection ());
mainwin_ptr->AskForNewConnection (soc);
Client_count++;
}

[mrjj]

it seems fine.
SOCKETptr should be the object u expect.