Accessing child function from base class
From what I understand, you propose like this:
- Outside your class, in your other code, you create a pointer variable of type base class and assign it a pointer to the derived class object.
// Child.mqh class CChild : protected CBase { private: protected: public: CChild () { } ~CChild () { return; } void update(); } void CChild::update() { Alert(mData); } CBase *child = new CChild();
- Then you call the pointers function "update" from the base class objects pointer. Since it is a derived object, the update function of the derived object gets called
// Base.mqh class CBase { private: protected: int mData; public: CBase () { mData = 1; update(); } ~CBase () { return; } void update(); } CBase::update() { child.update(); }
After tried the above method, I get error:
conversion from 'CChild *' to 'CBase *' is not accessible because of inheritance access
From what I understand, you propose like this:
- Outside your class, in your other code, you create a pointer variable of type base class and assign it a pointer to the derived class object.
- Then you call the pointers function "update" from the base class objects pointer. Since it is a derived object, the update function of the derived object gets called
After tried the above method, I get error:
conversion from 'CChild *' to 'CBase *' is not accessible because of inheritance access
Make the method virtual in the base class and call it.
conversion from 'CChild *' to 'CBase *' is not accessible because of inheritance access
Instead of instantiating from the base class and creating a pointer to the child class, why not just instantiate the child class?
I mean:
CChild child;
Instead of:
CBase *child = new CChild();
Maybe your goal is something else, but I played around with your code and could get a basic working version
- www.mql5.com
He can call Update() from base class since that Update be virtual
Instead of instantiating from the base class and creating a pointer to the child class, why not just instantiate the child class?
I mean:
Instead of:
Maybe your goal is something else, but I played around with your code and could get a basic working version
Thank you R4tna C.
The suggested way actually work. But after a few test, I found it cause buggy & my terminal become unresponsive.
Okey, now I understand what polymorphism is after seeing this documentation.
The polymorphism need an execution script.mq4 to execute it.
The update in base class is rarely called on script or ea, and it's only called once during onInit.
But it called multiple times from base class itself.
// Base.mqh class CBase { private: protected: int mData; public: CBase () { mData = 1; update(); } ~CBase () { return; } void update(); void Foo1(); void Foo2(); } void CBase::update() { child.update(); // child class } void CBase::Foo1() { // do something update(); // base class } void CBase::Foo2() { // do something update(); // base class }
Previously, all the code inside base and child file are in same file
// Base.mqh class CBase { private: protected: int mData; public: CBase () { mData = 1; update(); } ~CBase () { return; } void update(); void update1(); void update2(); } void CBase::update() { update1(); // called within the same class update2(); // called within the same class } void CBase::update1() { // do something } void CBase::update2() { // do something }
Because of there's too much line of code & the code become unreadable.
I refactored, separate the code into child.
I never work with virtual method before. And seeing the documentation, I understand the concept that Dominik Christian Egerts state: " It will be overwritten by the child class function "
But how to make the virtual method to be called in base class.
Could you provide some code example?
- docs.mql4.com
Thank you R4tna C.
The suggested way actually work. But after a few test, I found it cause buggy & my terminal become unresponsive.
That is a surprise as I use this approach a lot and have not had such issues. Were you by nay chance creating a new object on every tick?
That could consume a lot of memory - I am sure you know already, but it is better to instantiate once and re-use.
Also, what is it you are planning to do with this approach? Seems very involved and intricate
Thank you R4tna C.
The suggested way actually work. But after a few test, I found it cause buggy & my terminal become unresponsive.
Okey, now I understand what polymorphism is after seeing this documentation.
The polymorphism need an execution script.mq4 to execute it.
The update in base class is rarely called on script or ea, and it's only called once during onInit.
But it called multiple times from base class itself.
Previously, all the code inside base and child file are in same file
Because of there's too much line of code & the code become unreadable.
I refactored, separate the code into child.
I never work with virtual method before. And seeing the documentation, I understand the concept that Dominik Christian Egerts state: " It will be overwritten by the child class function "
But how to make the virtual method to be called in base class.
Could you provide some code example?
Here is the example. and the output.
class Base { public: Base(void) {;} ~Base(void) {;} void CallVirtualMethod(void) {VirtualMethod();} protected: virtual void VirtualMethod(void) {Print(__FUNCTION__, ", not implement...");} }; //+------------------------------------------------------------------+ //| | //+------------------------------------------------------------------+ class Chield1: public Base { public: Chield1(void){;} ~Chield1(void){;} protected: virtual void VirtualMethod(void) {Print(__FUNCTION__, ", Chield1...");} }; //+------------------------------------------------------------------+ //| | //+------------------------------------------------------------------+ class Chield2: public Base { public: Chield2(void){;} ~Chield2(void){;} protected: virtual void VirtualMethod(void) {Print(__FUNCTION__, ", Chield2...");} }; //+------------------------------------------------------------------+ //| | //+------------------------------------------------------------------+ void Fun(void) { Base* pointer; //--- pointer = new Base(); pointer.CallVirtualMethod(); delete pointer; //--- pointer = new Chield1(); pointer.CallVirtualMethod(); delete pointer; //--- pointer = new Chield2(); pointer.CallVirtualMethod(); delete pointer; }
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It is possible for base class execute function on child class?
Example:
I have base class as shown below. The constructor only execute update() function. And the update() function must execute the function that has on it child class
And the child class look like this:
As we can see in base class I have put CChild.update(). But that never work. What is the correct way to calling it.
Also if possible, suggest a best practice code style for above example
Thank you