In this blog post about dependency injection in C++, the author explain a hybrid approach that uses both templates and interfaces as follows:
ICar.h (publicly visible):
#pragma once
struct ICar
{
virtual void Drive() = 0;
virtual ~ICar() = default;
};
std::unique_ptr<ICar> MakeV8Car();
std::unique_ptr<ICar> MakeV6Car();
Car.h (internal):
#pragma once
#include "ICar.h"
template <typename TEngine>
class Car : public ICar
{
public:
void Drive() override
{
m_engine.Start();
// drive
m_engine.Stop();
}
private:
TEngine m_engine;
};
Car.cpp:
#include "Car.h"
#include "V8Engine.h"
#include "V6Engine.h"
std::unique_ptr<ICar> MakeV8Car()
{
return std::make_unique<Car<V8Engine>>();
}
std::unique_ptr<ICar> MakeV6Car();
{
return std::make_unique<Car<V6Engine>>();
}
All of which makes good sense to me, except for the internal part. Let's assume I've created a shared object from the above.
How is Car.h private in the context of this shared object?
I've read on the meaning of a private header in the answer which states:
Keep your data in MyClassPrivate and distribute MyClass.h.
Presumably meaning to not distribute MyClass_p.h, but how does one avoid distributing a header file and still have the .so work?
I'm running into an issue where I implemented a derived wxTimer class to override the Notify() call since I'm not using an owner implementation as described in the documentation.
When I debug the run, I can see
the timer is being instantiated
my_timer_instance->IsRunning() returns true
MyTimer::Notify() is never called
This leads me to believe that the timer is being set and running, but when it expires it's calling the base class Notify() procedure and not my override it's not calling notify() but I'm not sure why.
EDIT: I added frame->getTimer()->Notify(); to my app and the correct procedure was called. Therefore, the timer just isn't calling Notify when it expires.
EDIT2: Added this minimal working example, and the timer works as expected. I'll try to compare the two and see what the problem is.
MyApp.hpp
#pragma once
#ifndef __NONAME_H__
#define __NONAME_H__
#include <wx/artprov.h>
#include <wx/xrc/xmlres.h>
#include <wx/statusbr.h>
#include <wx/gdicmn.h>
#include <wx/font.h>
#include <wx/colour.h>
#include <wx/settings.h>
#include <wx/string.h>
#include <wx/frame.h>
#include <wx/timer.h>
///////////////////////////////////////////////////////////////////////////
class MyTimerClass : public wxTimer
{
wxFrame* MyFrame;
public:
MyTimerClass(wxFrame* frame): MyFrame(frame) {};
void Notify() override;
};
///////////////////////////////////////////////////////////////////////////////
/// Class MyFrame1
///////////////////////////////////////////////////////////////////////////////
class MyFrame1 : public wxFrame
{
private:
protected:
wxStatusBar* m_statusBar1;
MyTimerClass* MyTimer;
public:
void StartTimer(int TimeInSeconds);
MyFrame1(wxWindow* parent, wxWindowID id = wxID_ANY, const wxString& title = wxEmptyString, const wxPoint& pos = wxDefaultPosition, const wxSize& size = wxSize(500, 300), long style = wxDEFAULT_FRAME_STYLE | wxTAB_TRAVERSAL);
~MyFrame1();
};
#endif //__NONAME_H__
MyApp.cpp
#include "MyApp.hpp"
#include "wx/wxprec.h"
// for all others, include the necessary headers (this file is usually all you
// need because it includes almost all "standard" wxWidgets headers)
#ifndef WX_PRECOMP
#include "wx/wx.h"
#endif
///////////////////////////////////////////////////////////////////////////
void MyTimerClass::Notify()
{
MyFrame->SetStatusText("Timer popped", 0);
}
MyFrame1::MyFrame1(wxWindow* parent, wxWindowID id, const wxString& title, const wxPoint& pos, const wxSize& size, long style) : wxFrame(parent, id, title, pos, size, style)
{
MyTimer = new MyTimerClass(this);
this->SetSizeHints(wxDefaultSize, wxDefaultSize);
m_statusBar1 = this->CreateStatusBar(1, wxSTB_SIZEGRIP, wxID_ANY);
this->Centre(wxBOTH);
this->StartTimer(5);
}
void MyFrame1::StartTimer(int TimeInSeconds)
{
SetStatusText("Timer started with " + std::to_string(TimeInSeconds) + " seconds.");
MyTimer->Start(TimeInSeconds * 1000);
}
MyFrame1::~MyFrame1()
{
}
// ----------------------------------------------------------------------------
// resources
// ----------------------------------------------------------------------------
// the application icon (under Windows it is in resources and even
// though we could still include the XPM here it would be unused)
#ifndef wxHAS_IMAGES_IN_RESOURCES
#include "../sample.xpm"
#endif
// ----------------------------------------------------------------------------
// private classes
// ----------------------------------------------------------------------------
class MyApp : public wxApp
{
public:
virtual bool OnInit() wxOVERRIDE;
};
enum
{
// menu items
Minimal_Quit = wxID_EXIT,
Minimal_About = wxID_ABOUT
};
wxIMPLEMENT_APP(MyApp);
bool MyApp::OnInit()
{
// call the base class initialization method, currently it only parses a
// few common command-line options but it could be do more in the future
if (!wxApp::OnInit())
return false;
// create the main application window
MyFrame1 *frame = new MyFrame1(NULL, -1, "Test Frame");
frame->Show(true);
return true;
}
#BobbyTables,
From the documentation:
This member should be overridden by the user if the default
constructor was used and SetOwner() wasn't called.
Is it the case?
Nothing seems to be wrong in the code you show (although I'd change a few things, such as using raw pointer for my_timer_instance), so the problem must be elsewhere. As usual, the best would be to come up with a SSCCE, without it I can only offer some guesses as to what the problem actually is.
Are you running the event loop? The timers will only fire when it's running, so if you block doing some computation, this wouldn't happen.
Also, what is frame in Notify()? Is this a global (I'd rather pass it as parameter to MyTimer ctor)?
So after mimicking the code provided in the question, the following changes were made:
Instead of using a getter and setter to access the private timer member, I instead use
void refreshTimer(int time_in_seconds) in my parent frame class and create the timer in the parent frame's constructor rather than letting the app create it and pass it in.
I don't see why either of those two things would change the behavior of the timer but the timer now works as expected. I apologize for not being able to identify a concrete bug as the source of the problem.
NOTE: This behavior was caused by the timer being invoked outside the wxwindow's thread. Be careful when creating multithreaded programs using wxwidgets as a GUI. To circumvent this issue since I needed the timer to be invoked in a different thread, I created my own timer class that works correctly.
I hope I can explain myself.
Supose I have next:
File "A.h":
#include "C.h"
public class A{
// Some code...
}
File "B.h":
#include "A.h"
public class B{
A a = new A(); //With this line I mean I'm using one instance of "A" inside "B.h"
//Some code...
}
Is it possible to include "C.h" ONLY inside "A.h"?
My problem is that the code I've included is giving me a lot of conflicts with usual functions. It's not an option to correct conflicts one by one, because there is a huge set of them. Also, my "C.h" code included is only a test code: after some tests, I will delete the include line.
Is there any way of 'bubbling' my include?
Thank you in advance.
EDIT: A.h and B.h are on the same namespace.
Is it possible to include "C.h" ONLY inside "A.h"?
No. Not to my knowledge.
If you have name conflicts, just include C.h within an other namespace, as #user202729 proposed. This can help.
But I guess you use C in A for tests and you cannot use it in C in A without the implementation which is not compatible to C++Cli or content from B.h.
We used the pimpl ideom (pointer to implementation).
Example:
c++/clr currently does not allow do be included directly and that's why sometimes you cannot use libraries you want to use (like C.h), because they do rely on the support of .
This is my C.h ( used by all the other headers)
struct LockImpl; // forward declaration of C.
class C
{
public:
C();
virtual ~C();
public:
void Lock() const;
void Unlock() const;
LockImpl* _Lock;
};
This is my C.cpp (compiled without /clr )
#include <mutex>
struct LockImpl
{
std::mutex mutex;
};
C::C() : _Lock(new LockImpl()) {}
C::~C() { delete _Lock; }
void C::Lock() const
{
_Lock->mutex.lock();
}
void C::Unlock() const
{
_Lock->mutex.unlock();
}
A.h
#include "C.h"
public class A{
C c;
void someMethod()
{
c.Lock() // I used another template for a RAII pattern class.
c.Unlock()
}
}
I am working on a COM-style complier cross-compatible plugin framework relying on compatible virtual table implementations for ABI compatibility.
I define interfaces containing only pure virtual member functions and an overridden delete operator to channel destruction to the place of implementation.
This works well with extern "C" factory functions instantiating the plugin implementation of the interface and returning an interface-type pointer.
However, I was wondering if smart pointers wouldn't be a more modern way to manage the lifetime of the plugin object. I think I have actually managed to
create a standard-layout shared_ptr/weak_ptr that uses a reference count object defined and implemented the same way as the plugin interfaces.
It looks something like this:
class IRefCount
{
public:
virtual void incRef() = 0;
virtual void decRef() = 0;
virtual bool incRefIfNZ() = 0;
virtual void incWRef() = 0;
virtual void decWRef() = 0;
virtual long uses() const = 0;
protected:
~ref_count_base() = default; //prohibit automatic storage
}
template <typename Ty>
class shared_ptr
{
private:
Ty* ptr_;
IRefCount* ref_count_;
public:
//member functions as defined by C++11 spec
}
Three questions:
Before the smart pointer the factory function looked like this:
extern "C" IPlugin* factory() { try { return new Plugin(); } catch (...) { return nullptr; } }
Now, it looks like this:
extern "C" shared_ptr<IPlugin> factory() { try { return shared_ptr<IPlugin>(new Plugin()); } catch (...) { return nullptr; } }
VS2013 is giving me warning C4190: 'factory' has C-linkage specified, but returns UDT 'shared_ptr' which is incompatible with C. According to MSDN this is OK, provided that both caller and callee are C++.
Are there any other potential issues with returning standard-layout objects from "C" linkage functions?
Calling conventions. Should I be specifying __stdcall for all pure-virtual interface functions and factory functions?
I am using <atomic> for the reference count. I am writing platform-independent code and I have not yet tried compiling for ARM. According to http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dht0008a/ch01s02s01.html armcc does not implement std::atomic. Any better compilers/stl out there?
EDIT: What is C++/CLI? I am programming in Visual studio, and as far as I know using C++... Also, The first error was solved by Peter's comment, but I am still stuck on the second.
I am brand new to the world of C++, and have previously done all my work in Java. I am unfamiliar with the use of pointers and garbage collection (though I believe I understand the concept) and I believe that may be the source of my problems. I am getting the following error messages:
1>Runner.cpp(6): error C3145: 'formOutOfTime' : global or static variable may not have managed type 'System::Windows::Forms::Form ^'
1> may not declare a global or static variable, or a member of a native type that refers to objects in the gc heap
1>Runner.cpp(22): error C2061: syntax error : identifier 'FormOutOfTime'
My code is like this:
PurpleHealth.cpp (This is the file I believe the system calls to start it all off):
#include "FormOutOfTime.h"
#include "FormParentalOverride.h"
#include "Runner.h"
using namespace PurpleHealth;
[STAThreadAttribute]
int main(array<System::String ^> ^args)
{
// Enabling Windows XP visual effects before any controls are created
Application::EnableVisualStyles();
Application::SetCompatibleTextRenderingDefault(false);
// Create the main window and run it
//Application::Run(gcnew FormOutOfTime());
Runner* runner = new Runner();
//delete runner;
return 0;
}
Runner.h (this is the header file I want to run all my main code, and launch the forms. I also struggle with the purpose behind the header files)
#include "stdafx.h"
#include "FormOutOfTime.h"
#include "FormParentalOverride.h"
class Runner
{
public:
Runner();
~Runner();
// functions
private:
void Go();
// member variables
};
And Finally Runner.cpp:
#include "stdafx.h"
#include "Runner.h"
#include "FormOutOfTime.h"
#include "FormParentalOverride.h"
//Variable Dclaration
System::Windows::Forms::Form^ formOutOfTime;//Error Here***************************
Runner::Runner()
{
// Do stuff if you need to
this->Go();
}
Runner::~Runner()
{
// Clear memory if you need to
}
void Runner::Go()
{
formOutOfTime = gcnew FormOutOfTime();//Error Here***************************
formOutOfTime->ShowDialog();
}
Please help me solve these messages, and even critique on form is appreciated. Thanks.
managed pointers cannot be declared at static or global scope. They can only be declared at function scope. Move the declaration of formOutOfTime from the top of the runner.cpp file to within the Go method