I have a struct A that inherits from other classes (which I'm not allowed to change). Inside A and it's methods I can call inherited methods (lets say A_method(int i), for example) without problem but when I tried to write a nested struct (lets say In) and call A_method(int i) and there is were I'm stuck.
The initial code looks like this, and I can't change it, is some kind of college assigment.
#include "Player.hh"
struct A : public Player {
static Player* factory () {
return new A;
}
virtual void play () {
}
};
RegisterPlayer(PLAYER_NAME);
Then I tried this:
#include "Player.hh"
struct A : public Player {
static Player* factory () {
return new A;
}
//My code
struct In {
int x;
void do_smthing() {
A_method(x);
}
}
virtual void play () {
}
};
RegisterPlayer(PLAYER_NAME);
Ok, from a beginning I knew I could't do this, for In to see it's parent class it should have a pointer to it but In is a often instantiated object in my code and I wanted to avoid passing this constantly to a constructor so I tried this aproach:
#include "Player.hh"
struct A : public Player {
static Player* factory () {
return new A;
}
//My code
static struct Aux
A* ptr;
Aux(A* _p) { ptr = _p; }
} aux;
struct In {
int x;
void do_smthing() {
aux.ptr->A_method(x);
}
}
virtual void play () {
//the idea is to call do_smthing() here.
}
};
RegisterPlayer(PLAYER_NAME);
What I want to avoid (if possible) is something like this:
struct In {
int x;
A* ptr;
In (A* _p) : ptr(_p) {}
void do_smthing() {
ptr->A_method(x);
}
}
The main reason for this: I have more struct definitions and they they are instantiated multiple times through the rest of the (omitted) code, and I don't like the idea of seeing In(this) so many times.
I don't know if I'm completly missing something or what I want to do it's just not possible... Please ask for clarifications if necessary.
(Also, performance is kind of critical, my code will be tested with limited CPU time so I kinda have to avoid expensive approachs if possible. Using C++11)
There is no way you can skip passing the this pointer. Instead, you could create a helper function in A:
template <typename InnerType, typename ...Params>
InnerType makeInner(Params&&... params)
{
return InnerType(this, std::forward<Params>(params)...);
}
Then you can use
auto * a = A::factory();
auto inner = a->makeInner<A::In>();
I have some suggestions which are not directly related to you question but may help:
A::facotry() returns a std::unique_ptr<A> instead of raw pointer
Try to describe what problem you are trying to solve. I have a strong feeling that there can be a better design other than creating many nested structs.
I don't see passing a this pointer could have any impact on the performance. The more important thing is to identify the path that is latency-sensitive and move expensive operations out of those paths.
Related
The crux of the issue is I want to create a vector of base pointers to reference children objects. However I'm having issues accessing the methods of the children. I've seen examples of downcasting online but I don't feel it's the best thing for me since I want to keep my code generic. Please look below for a sample of what I'm trying to accomplish.
class Base
{
public:
stuffx;
private:
stuffy;
}
template<typename U>
class Child : public Base
{
public:
Child(
std::function<U()> getterFunc,
std::function<void(U)> setterFunc
):
mgetter(getterFunc),
msetter(setterFunc)
{
}
U getFunction() const {return m_getter();}
void setFunction(U input) const {return m_setter(input);}
private:
observableValues() {}
std::function<U()> m_getter;
std::function<void(U)> m_setter;
}
int main()
{
std::vector<std::shared_ptr<Base>> Dummy = {std::make_shared<Child<int>> (std::bind(..), std::bind(...)),
std::make_shared<Child<string>> (std::bind(..), std::bind(...)) };
Dummy.at(0)->getGFunction(); // this throws an error as out of scope.
(dynamic_cast<Child<int>>(Dummy.at(0))->getGFunction(); // this is ok
}
In this example above my vector is of size 2 which is manageable but my goal is to serialize c++ classes to a psql server and may have to handle vectors of size 30+. My next question is is there a way to automate this in a for loop taking into the account the type deduction that may need to be performed for typename U.
int main()
{
std::vector<std::shared_ptr<Base>> Dummy = {std::make_shared<Child<int>> (std::bind(..), std::bind(...)),
std::make_shared<Child<string>> (std::bind(..), std::bind(...)) };
std::vector<std::shared_ptr<Base>>::const_iterator it_base = Dummy.begin();
for (; it_base != Dummy.end(); ++it_base)
{
//insert method here for downcasting
}
}
I am inspecting the code that may cause memory leak. I know something is wrong with std::set.erase(this) and the destructor of SomeObject. So how to fix it?
class SomeObject;
////....
std::set<SomeObject*> managedObjects;
///.....
class SomeObject{
public:
SomeObject(){ managedObjects.insert(this); }
SomeObject(SomeObject&& S)/*move cter*/{ managedObjects.insert(this); }
virtual ~SomeObject() { managedObjects.erase(this); }
////....
};
////....
void clearAllObjects() {
for(auto p : managedObjects){
if(p){
delete p;
}
}
managedObjects.clear();
}
////....
When you delete inside clearAllObjects() it will result in managedObjects.erase(this) which is the same as managedObjects.erase(p).
This means that the internal iterator in the range based for-loop may be invalidated (I'm not sure). If it is, it'll try to do ++internal_iterator; on an invalid iterator - with undefined behavior as a result.
To be safe, you could copy the iterator and step that to the next in the set before doing erase.
Also note: There's no need to check if what you delete is a nullptr or not. It's mandated by the standard to have no effect if that's the case.
Example:
void clearAllObjects() {
for(auto pit = managedObjects.begin(); pit != managedObjects.end();) {
delete *pit++ // postfix ++ returns a copy of the old iterator
}
managedObjects.clear();
}
A side effect by having this managedObjects set is that you can't have automatic variables of SomeObject.
int main() {
SomeObject foo;
clearAllObjects(); // deletes the automatic object "foo" (not allowed)
} // <- the automatic object is destroyed here
There is a custom defined map, with an element std::function()>.
The lambda code is working, but I don't know how to expand it to a normal formation. The code is following.
class TestA{
public:
TestA() {}
~TestA() {}
TestA(const TestA &) {}
static void print()
{
cout << __FUNCTION__ << endl;
return;
}
};
void testComplexMap1()
{
typedef map<string, std::function<std::unique_ptr<TestA>()>> TempMap;
TempMap m;
// the lambda format code, it works
//m.insert({ "TestA", []() {return std::unique_ptr<TestA>(new TestA());}});
// I want to expand it, but failed.
TestA *t = new TestA();
//function<unique_ptr<TestA>()> fp(unique_ptr<TestA>(t));
function<unique_ptr<TestA>()> fp(unique_ptr<TestA>(t)()); //warning here
//m.emplace("TestA", fp); // compile error here
}
Any help will be greatly appreciated.
fp is not initialized with a function so compilation fails.
You can expand it like this:
TestA *t = new TestA();
std::unique_ptr<TestA> UT(t);
auto func = [&]() { return move(UT);};
std::function<std::unique_ptr<TestA>()> fp(func);
m.emplace("TestA", fp);
See DEMO.
In C++ everything that looks like it could be a declaration is treated as such.
This means the line
function<unique_ptr<TestA>()> fp(unique_ptr<TestA>(t)());
is interpreted as:
fp is the declaration of a function returning an std::function<unique_ptr<TestA>()> and expecting a parameter called t which is a function pointer to a function returning a std::unique_ptr<TestA> and getting no parameter. (Which is not what you intended.)
This also means that the t in this line is not the same t as in the previous line.
You have to pass fp something that is actually callable like this:
std::unique_ptr<TestA> f() {
return std::make_unique<TestA>();
}
void testComplexMap1() {
// ...
function<unique_ptr<TestA>()> fp(f);
m.emplace("TestA1", fp);
}
If you want to add a function to the map that wraps an existing pointer into a unique_ptr you would need either a functor:
class Functor {
public:
Functor(TestA * a) : m_a(a) {}
~Functor() { delete m_a; }
std::unique_ptr<TestA> operator()(){
auto x = std::unique_ptr<TestA>(m_a);
m_a = nullptr;
return std::move(x);
}
private:
TestA * m_a;
};
void testComplexMap1() {
//...
TestA * t = new TestA();
m.emplace("TestA", Functor(t));
}
Or a lambda with capture:
void testComplexMap1() {
//...
TestA * t = new TestA();
m.emplace("TestA", [t](){ return std::unique_ptr<TestA>(t); });
}
The lamda is translated more or less to something like the Functor class. However in each case you have to be really careful: The functions in the map that encapsulate an existing pointer into a std::unique_ptr can and should only be called once.
If you don't call them, memory allocated for t won't be freed. If you call them more than once you get either a std::unique_ptr to nullptr (in my Functor class variant) or a more than one std::unique_ptr tries to manage the same memory region (in the lambda with capture variant), which will crash as soon as the second std::unique_ptr is deleted.
In short: I would advice against writing code like this and only put functions in the map that are callable multiple times.
I have the following base class:
class node_layer_manager_t : public layer_manager_t
{
protected:
//Devices
trx_t trx;
private:
std::vector<string> trx_dump_labels;
public:
node_layer_manager_t( xml::node_t& params );
~node_layer_manager_t();
virtual bool set_profile(void) override;
}
I created the following derived class:
class node_layer_manager_with_rad_t : public node_layer_manager_t
{
protected:
//Devices
radio_t radio;
public:
node_layer_manager_with_rad_t(xml::node_t& params );
~node_layer_manager_with_rad_t();
virtual bool set_profile(void) override;
virtual void radio_monitoring_job_function(void);
intervalues_t<double> radio_tmp;
ushort duration_seconds_for_radio_monitoring;
};
I want it so that the set profile will execute the set_profile of the base class and in addition some other action.
Can I just write it this way?
bool node_layer_manager_with_rad_t::set_profile(void)
{
bool success;
node_layer_manager_t::set_profile();
try
{
string_t profile_tag = "logs/trx_dump/node:"+get_id();
dev_tx = profile->get_decendant(profile_tag.c_str());
cout<<"sarit id= "<< get_id()<<endl;
success = true;
}
catch(...)
{
cout<<"sarit profile error: "<<endl;
success = false;
}
return success; //**
}
**Or should I reurn the follwing:
return (success && node_layer_manager_t::set_profile());
If you have to call parent set_profile regardless what you have to do in derived class, you should adopt design which take care about this constraint.
Typically, you should mark based class set_porfile as final and manage call of a dedicated derived class method inside based class:
class node_layer_manager_t : public layer_manager_t
{
protected:
....
// set_profile actions of derived class
// proposed a default without side effect implementation if
// derived class doesn't need to overload this.
virtual bool set_profile_child() { return true; };
private:
....
public:
.....
// Manage here call of derived
virtual bool set_profile() override final
{
// actions before derived specific actions
....
// Call specific derived class actions
bool success = set_profile_child();
// actions after derived specific actions
if (success)
{
//do based class action
}
return success;
}
}
and in child:
class node_layer_manager_with_rad_t : public node_layer_manager_t
{
protected:
....
public:
virtual bool set_profile_child() override;
};
// Manage only there own action, regardless of needs of based class
bool node_layer_manager_with_rad_t::set_profile(void)
{
try
{
// Do what you're in charge, and only what you're in charge!
}
catch(...)
{
cout<<"sarit profile error: "<<endl;
success = false;
}
return success; //**
}
With this kind of design, each class do only what it have to manage, and only its. Derived class doesn't have to deal with needs of based class.
If you want to offer to your derived class ability to decided if code is executed before or after generic behavior, you can replace or add to set_profile_child() two methods: bool pre_set_profile() and bool post_set_profile()
At first, you haven't declared success anywhere (so actually, this is not a mcve, the code should not compile as is).
Still I get it - and tThe answer is: it depends on what you actually want to do...
Do you want to call the super class first or after the sub class code? Your example implies the former, your alternative the latter. Do you want to abort if the super class function fails or still execute your code?
Your inital example calls the super class function, ignores the result and does its own stuff afterwards.
This calls the super class function first and continues only on success:
bool success = node_layer_manager_t::set_profile();
if(success)
{
try { /*...*/ } // <- no need to set success to true, it is already
catch(...) { /*...*/ success = false; }
}
This executes both, but combines the result:
bool success = node_layer_manager_t::set_profile();
try { /*...*/ } // <- do not modify success, must remain false if super class failed!
catch(...) { /*...*/ success = false; }
Your alternative hints to executing the sub class code first and only call the super class function, if nothing went wrong.
Any of these approaches might be appropriate, none of them might be. You have to get a clear image of what your requirements are - and then implement the code such that your needs are satisfied...
I'm writing a simple, lightweight engine in D. For the input calls I use GLFW3. The library in question uses callbacks to send input events to the program.
What I would like is to use a method from a class as the callback function, rather than a function. This is proving difficult (just as it is in C++). I believe there is an elegant way to do it, but this is how I got it right now.
public void initialise(string logPath) {
[...]
m_Window = new RenderWindow();
m_Window.create();
// Lets set up the input loop.
GLFWkeyfun keyCB = function(GLFWwindow* win, int key, int scancode, int action, int mods) {
printf("Got key event: %d:%d:%d:%d\n");
RenderWindow rw = Root().getRenderWindow();
switch (key) {
case KeyboardKeyID.Q:
glfwSetWindowShouldClose(win, true);
break;
case KeyboardKeyID.H:
if (rw.hidden) {
rw.show();
} else {
rw.hide();
}
break;
default:
break;
}
};
glfwSetKeyCallback(m_Window.window, keyCB);
}
Here is the definition of the callback setting function and type:
extern (C) {
alias GLFWkeyfun = void function(GLFWwindow*, int, int, int, int);
GLFWkeyfun glfwSetKeyCallback(GLFWwindow*, GLFWkeyfun);
}
What I would like to do instead, is create a method that is part of the class. Is there any way to do this?
A solution I tried was a static method wrapped around in extern (C), this worked for calling it, but then I could (obviously) not access this or any other methods, which defeats the point of the exercise.
Thanks in advance.
The way I'd do it is to have a static map of the pointers to the class, so like:
static YourWindowClass[GLFWwindow*] mappings;
Then, in the constructor, once you get a GLFWwindow pointer, add it right in:
mappings[m_Window.window] = this;
Now, make the static extern(C) function to use as the callback. When it gets a pointer from C, look up your class reference in that mappings array and then go ahead and call the member function through that, forwarding the arguments.
So a bit of an extra step, but since it doesn't look like the callback lets you pass user-defined data to it (BTW, attention all lib writers: user-defined void* to the callbacks is sooooo useful, you should do it whenever possible!), but since it doesn't do that the associative array is the next best thing.
Well, I have figured it out my own. The solution I went with was a Singleton class InputManager. Instances of RenderWindow attach themselves to it with the following function. The InputManager then creates an anonymous function() for the RenderWindow that receives events, which then calls a function that handles the actual event.
The idea is then that listeners attach themselves to the InputManager and receive keyboard events for the RenderWindow they requested.
class InputManager {
private static InputManager m_Instance;
private RenderWindow[] m_Watched;
private KeyboardListener[][RenderWindow] m_KeyListeners;
public void recvKeyEvent(GLFWwindow* w, int k, int c, int a, int m) {
writeln("Received key: ", k);
}
public void watch(RenderWindow win) {
if (!isWatched(win)) {
// Relay the key callbacks onto the InputManager.
GLFWkeyfun keyCB = function(GLFWwindow* w, int k, int c, int a, int m) {
InputManager().recvKeyEvent(w, k, c, a, m);
};
glfwSetKeyCallback(win.window, keyCB);
}
}
private bool isWatched(RenderWindow win) {
foreach(RenderWindow w; m_Watched) {
if (win == w) {
return true;
}
}
return false;
}
public static InputManager opCall() {
if (m_Instance is null) {
m_Instance = new InputManager();
}
return m_Instance;
}
private this() {
// nothing
}
}
Works like a charm, now to figure out how to properly attach listeners elegantly.
For those curious, the full source code with how this is set up can be found at https://github.com/Adel92/Mage2D. I hope it helps someone else in a similar position with callbacks.