Circular include problem

I have entered into a circular include problem. I have a class:

Code:

---

#include "TestConnection.h"
#include "oci.h"
#include "SU_ORADB_imp.h"

class DBTestConnection final : public Connection
{
private:
        SU_ORADB_imp* imp_{ nullptr };
        bool m_connected = false;
        // methods
        DBTestConnection();
        // friend class
        friend ConnectionPoolFactory<DBTestConnection>;

public:
        bool heart_beat() override { return m_connected; }
        bool is_healthy() override { return m_connected; }
        void disconnect() override;
        bool connect() override;
        void do_something();
        ~DBTestConnection() override;
        OCISvcCtx* GetServerContext() { return imp_->_svchp; }
};

---

and another class:

Code:

---

#pragma once

#include "oci.h"
#include "ConnectionFactory.h"

class SU_ORADB_imp
{
private:
        OCISvcCtx* _svchp;        // just for testing purpose
        // methods
        void Init();

protected:
        PoolProxy GetConnection();
        static std::unique_ptr<ConnectionPool> pool_;

public:
        void Connect();
        void Disconnect();
        SU_ORADB_imp();
        ~SU_ORADB_imp();
        void DoSqlSelect();

        friend class DBTestConnection;
};

---

but I got these errors:

Code:

---

dbtestconnection.h(10): error C2143: syntax error: missing ';' before '*'
dbtestconnection.h(10): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
dbtestconnection.h(10): error C2334: unexpected token(s) preceding '{'; skipping apparent function body
dbtestconnection.h(24): error C2065: 'imp_': undeclared identifier

---

and

Code:

---

connectionfactory.h(11): error C2065: 'DBTestConnection': undeclared identifier
connectionfactory.h(12): error C2923: 'ConnectionPoolFactory': 'DBTestConnection' is not a valid template type argument for parameter 'T'
connectionfactory.h(27): error C2913: explicit specialization; 'ConnectionPoolFactory' is not a specialization of a class template

---

How can I get rid of this issue ? Can you help me a little bit ? I put here a test project to illustrate my problem.

Is this a circular class reference problem - both classes referring to each other?

If yes, then you need to forward declare one class before it is used in the other. Note that if this is the problem and you do this, you can only access the members of the forward declared class in the other via pointers - other you get an error message re incomplete class.

Code:

---

struct Fclass;

struct Myclass {
        Fclass* fclas {};

        Myclass() {}
        Myclass(Fclass* fc) : fclas(fc) {}
};

struct Fclass {
        Myclass mclas;
};

int main()
{
        Fclass fc;
        Myclass mc(&fc);
}

---

If this isn't the problem, can you provide a simple one file compilable example.

I have the class DBTestConnection:

Code:

---

#include "SU_ORADB_imp.h"

class DBTestConnection final : public Connection
{
private:
        SU_ORADB_imp* imp_{ nullptr };
...

---

error:

Code:

---

dbtestconnection.h(10): error C2143: syntax error: missing ';' before '*'

---

of course, I tried to declare only this class:

Code:

---

class SU_ORADB_imp;

class DBTestConnection final : public Connection
{
private:
        SU_ORADB_imp* imp_{ nullptr };
...

---

the I got

Code:

---

dbtestconnection.h(27): error C2027: use of undefined type 'SU_ORADB_imp'

---

I mean, when I am trying to use this memeber (imp_). Seems it is an endless loop around the tale.

How and where are you using imp_ ? Can you provide a minimal test compilable program that shows the problem.

A quick attempt to fix your problem did not lead to success.
I would try the following:
- disable the precompiled header
- in each file that is reported to have errors: comment out all includes, and try to get it to compile with forward declarations
- move all implementation from .h to .cpp files
- move the definition of the factory to a single header file

I have simplified the sample project, and after few changes, I left just one point error:

Code:

---

connectionfactory.h(8): error C2065: 'DBTestConnection': undeclared identifier
connectionfactory.h(9): error C2923: 'ConnectionPoolFactory': 'DBTestConnection' is not a valid template type argument for parameter 'T'
connectionfactory.h(23): error C2913: explicit specialization; 'ConnectionPoolFactory' is not a specialization of a class template

---

and that error fire here:

Code:

---

#pragma once

#include "connection.h"
#include "pool.h"
#include "DBTestConnection.h"

template <>
class ConnectionPoolFactory<DBTestConnection>  // <--- error
{
public:
        static std::unique_ptr<ConnectionPool> create(const std::uint16_t& num_connections)
        {
                std::vector<std::unique_ptr<Connection>> connections;
                for (std::uint16_t k = 0; k < num_connections; ++k)
                {
                        connections.emplace_back(std::unique_ptr<DBTestConnection>(new DBTestConnection{}));
                }
                return std::unique_ptr<ConnectionPool>(new ConnectionPool{ std::move(connections) });
        }

private:
        ConnectionPoolFactory() = default;
};

---

Provide a minimal test compilable program that shows the problem - one .cpp file of at most a couple of dozen lines (no .h files etc) that can be pasted here and copy/pasted easily into the compiler. Providing a zip file consisting of multiple .h/.cpp files within a project isn't really going to help.

I agree with 2kaud.
The posted zip projects are two complicated for investigations since there is a lot of relationships between classes, headers and sources files (plus a lot of or, I'd say, too many #includes!).

Try this DBTestConnection.h

Code:

---

#pragma once

#include "TestConnection.h"
#include "connection.h"
//#include "SU_ORADB_imp.h"
#include "oci.h"
//#include "ConnectionFactory.h"

class SU_ORADB_imp;

class DBTestConnection final : public Connection
{
private:
        SU_ORADB_imp* imp_{ nullptr };
        bool m_connected = false;
        // methods
        DBTestConnection();
        // friend class
        //friend ConnectionPoolFactory<DBTestConnection>;
        template <typename T>
        friend class ConnectionPoolFactory;// <DBTestConnection>

public:
        void disconnect() override;
        bool connect() override;
        void do_something();
        ~DBTestConnection() override;
        OCISvcCtx* GetServerContext();
};

---

The problem is
a) in DBTestConnection.h you include ConnectionFactory.h, which then needs to know class DBTestConnection. But the compiler has not seen a declaration of it at that point.
b) your friend declaration is incorrect, but the compiler didn't even come to that point.

Thank you a lot Richard !