Extending MqlTick

[Hannan Nussbaum]

Hello,

I need to extend MqlTick struct to include additional info such as symbol and AccountPlatform.

How can it be done?

[Fernando Carreiro]

Hannan Nussbaum: I need to extend MqlTick struct to include additional info such as symbol and AccountPlatform. How can it be done?

You can't "extend" a structure, especially not one used internally by the built-in functions. You can however define your own "similar" structures for your own functionality.

[Alain Verleyen]

Fernando Carreiro:

You can't "extend" a structure, especially not one used internally by the built-in functions. You can however define your own "similar" structures for your own functionality.

Yes you can inherit from a structure.

struct CustomTick:MqlTick
  {
   string   symbol;
   int      account;   
  };

However with MqlTick, you will not be able to use it in function like SymbolInfoTick().

[William Roeder]

1. Hannan Nussbaum: How can it be done?

   You just do it. Structs can only extend structs and classes only classes.

2. Alain Verleyen: However you will not be able to use it in function like SymbolInfoTick().

   Sure you can, just like you can pass a subclass object to a function taking the superclass.
   

[Alain Verleyen]

whroeder1:

1. 
   

2. Sure you can, just like you can pass a subclass object to a function taking the superclass.
   

Right it works for SymbolInfoTick().

But it doesn't with MqlRates and CopyRates() (compiles but gives runtime error 4029: Invalid Array). So I would suggest anyone to check before relying on such solution for internal mql structure.

[Hannan Nussbaum]

I am using this code to save and load tick to file memory. It expects MqlTick and throws parameter conversion error with the custom struct. Any solution?

#property copyright "Copyright 2017, MetaQuotes Software Corp."

#property link      "https://www.mql5.com"

#property strict

#include <MemMapLib.mqh>

#include <TypeToBytes.mqh>

template <typename T>

class EXCHANGE_DATA

{

private:

  CMemMapFile* FileMemory;

public:  

  EXCHANGE_DATA( const int Amount, const bool ModeCreate = false, string FileName = "Local\\test" )

  {

//    FileName += _Symbol;

    

    this.FileMemory = new CMemMapFile;

      

    if (this.FileMemory.Open(FileName, sizeof(T) * Amount + sizeof(int) + HEAD_MEM, ModeCreate ? modeCreate : modeOpen) != 0)

    {

      Alert("FileMemory.Open - ERROR!");

      

      delete &this;

    }

  }

  

  ~EXCHANGE_DATA( void )

  {

    this.FileMemory.Close();

    

    delete this.FileMemory;

  }

  void DataSave( const T &Data[], const bool FromBegin = true  ) const

  {

    const int Size = ::ArraySize(Data) * sizeof(T);

    uchar Bytes[];

    

    _ArrayCopy(Bytes, _R(Size).Bytes);              // Записали количество  

    _ArrayCopy(Bytes, _R(Data).Bytes, sizeof(int)); // Записали данные

  

        if (FromBegin)

          this.FileMemory.Seek(0, SEEK_SET);

  

        this.FileMemory.Write(Bytes, ::ArraySize(Bytes)); // Сбросили все в память

    

    return;

  }

  

  int DataLoad( T &Data[], const bool FromBegin = true ) const

  {

        if (FromBegin)

          this.FileMemory.Seek(0, SEEK_SET);

  

        uchar Bytes[];

          

        this.FileMemory.Read(Bytes, sizeof(int));  // Прочли из памяти количество данных        

        this.FileMemory.Read(Bytes, _R(Bytes)[0]); // Получили сами данные

  

        _ArrayCopy(Data, Bytes);              // Сбросили данные в массив

    

    return(::ArraySize(Data));

  }  

};

[Sergey Golubev]

Hannan Nussbaum:

...

Forum on trading, automated trading systems and testing trading strategies

Hello,

Please EDIT your post and use the SRC button when you post code. 

Thank you.

[Fernando Carreiro]

Alain Verleyen:

Yes you can inherit from a structure.

However with MqlTick, you will not be able to use it in function like SymbolInfoTick().

Thanks! Did not know that!

[Fernando Carreiro]

whroeder1:

1. You just do it. Structs can only extend structs and classes only classes.

2. Sure you can, just like you can pass a subclass object to a function taking the superclass.
   

Thanks! Did not know that!

[Hannan Nussbaum]

static CustomTick Ticks[1];

ExchangeTicks.DataSave(Ticks, true);

Error: 'Ticks' - parameter conversion not allowed

What can be done to solve this? When using the standard MqlTick is works fine.

(DataSave method see above code in class EXCHANGE_DATA)

[William Roeder]

You can derive from a structure just fine. You can't use an array of the derived in place of an array of the base. You'll have to copy each element yourself.