MetaTrader 4 Build 900: Class Templates in MQL4 and Optimized Memory Use

Release Notes: MetaTrader 4

22 October 2015

Terminal

  1. Fixed changing a password for an inactive (unconnected) account.




  2. Optimized use and release of memory when working with large amounts of historical data.
  3. Fixed and optimized working with a large number of news categories.

Signals

  1. Fixed unsubscribing from signals via the Navigator window context menu.



MQL4

  1. Added class templates allowing you to create parametrized classes like in C++. That enables even greater abstraction and ability to use the same code for working with objects of different classes in a uniform manner. An example of using:
    //+------------------------------------------------------------------+
    //|                                                    TemplTest.mq5 |
    //|                        Copyright 2015, MetaQuotes Software Corp. |
    //|                                             https://www.mql5.com |
    //+------------------------------------------------------------------+
    #property copyright "Copyright 2015, MetaQuotes Software Corp."
    #property link      "https://www.mql5.com"
    #property version   "1.00"
    //+------------------------------------------------------------------+
    //| Declare a template class                                         |
    //+------------------------------------------------------------------+
    template<typename T>
    class TArray
      {
    protected:
       T                 m_data[];
    
    public:
    
       bool              Append(T item)
         {
          int new_size=ArraySize(m_data)+1;
          int reserve =(new_size/2+15)&~15;
          //---
          if(ArrayResize(m_data,new_size,reserve)!=new_size)
             return(false);
          //---
          m_data[new_size-1]=item;
          return(true);
         }
       T                 operator[](int index)
         {
          static T invalid_index;
          //---
          if(index<0 || index>=ArraySize(m_data))
             return(invalid_index);
          //---
          return(m_data[index]);
         }   
      };
    //+------------------------------------------------------------------+
    //| Template class of a pointer array. In the destructor, it deletes |
    //| the objects, the pointers to which were stored in the array.     |
    //|                                                                  |
    //| Please note the inheritance from the TArray template class       |
    //+------------------------------------------------------------------+
    template<typename T>
    class TArrayPtr : public TArray<T *>
      {
    public:
       void             ~TArrayPtr()
         {
          for(int n=0,count=ArraySize(m_data);n<count;n++)
             if(CheckPointer(m_data[n])==POINTER_DYNAMIC)
                delete m_data[n];
         }
      };
    //+------------------------------------------------------------------------+
    //| Declare the class. Pointers to its objects will be stored in the array |
    //+------------------------------------------------------------------------+
    class CFoo
      {
       int               m_x;
    public:
                         CFoo(int x):m_x(x) { }
       int               X(void) const { return(m_x); }
      };
    //+------------------------------------------------------------------+
    //|                                                                  |
    //+------------------------------------------------------------------+
    TArray<int>     ExtIntArray;   // instantiate TArray template (specialize TArray template by the int type)
    TArray<double>  ExtDblArray;   // instantiate TArray template (specialize TArray template by the double type)
    TArrayPtr<CFoo> ExtPtrArray;   // instantiate TArrayPtr template (specialize TArrayPtr template by the CFoo type)
    //+------------------------------------------------------------------+
    //| Script program start function                                    |
    //+------------------------------------------------------------------+
    void OnStart()
      {
    //--- fill arrays with data
       for(int i=0;i<10;i++)
         {
          int integer=i+10;
          ExtIntArray.Append(integer);
          
          double dbl=i+20.0;
          ExtDblArray.Append(dbl);
          
          CFoo *ptr=new CFoo(i+30);
          ExtPtrArray.Append(ptr);
         }
    //--- output the array contents
       string str="Int:";
       for(i=0;i<10;i++)
          str+=" "+(string)ExtIntArray[i];      
       Print(str);   
       str="Dbl:";
       for(i=0;i<10;i++)
          str+=" "+DoubleToString(ExtDblArray[i],1);
       Print(str);   
       str="Ptr:";
       for(i=0;i<10;i++)
          str+=" "+(string)ExtPtrArray[i].X();      
       Print(str);
    //--- CFoo objects created via new should not be deleted, since they are deleted in the TArrayPtr<CFoo> object destructor  
      }
    Execution result:
    TemplTest EURUSD,M1: Ptr: 30 31 32 33 34 35 36 37 38 39
    TemplTest EURUSD,M1: Dbl: 20.0 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0
    TemplTest EURUSD,M1: Int: 10 11 12 13 14 15 16 17 18 19
  2. Fixed memory reallocation in the ArrayCopy function that could occasionally cause crashes of MQL4 programs.

Tester

  1. Fixed an error that occasionally caused nulling of the variables declared on the global level after testing an indicator.
  2. Fixed testing when connection to a trade server is lost.

MetaEditor

  1.  Fixed defining a function name in MetaAssist in the presence of type casting.
  2. Fixed opening large files.
  3. Added F hotkey to call the search function from the Code Base tab, as well as multiple tips in the status bar for the commands for working with a code: increasing/decreasing indentation, navigation, case shift, etc.


Fixed errors reported in crash logs.