MQL4 Reference Constants, Enumerations and Structures Named Constants Other constants

Other constants

Special constants are used to indicate parameters and variables states. It can be one of the following values:

Constant	Description	Value
NULL	Zero for any types. Also indicates empty state of the string	0
EMPTY	Indicates empty state of the parameter	-1
EMPTY_VALUE	Empty value in an indicator buffer. Default custom indicator empty value	2147483647 (0x7FFFFFFF)
CLR_NONE, clrNONE	Absence of color. Indicates empty state of colors	-1
CHARTS_MAX	The maximum possible number of simultaneously open charts in the terminal	100
INVALID_HANDLE	Incorrect handle	-1
IS_DEBUG_MODE	Flag that a mql4-program operates in debug mode	non zero in debug mode, otherwise zero
IS_PROFILE_MODE	Flag that a mql4-program operates in profiling mode	non zero in profiling mode, otherwise zero
WHOLE_ARRAY	Used with array functions. Indicates that all array elements will be processed. Means the number of items remaining until the end of the array, i.e., the entire array will be processed	0
WRONG_VALUE	The constant can be implicitly cast to any enumeration type	-1

The NULL constant can be assigned to a variable of any simple type or to an object structure or class pointer. The NULL assignment for a string variable means the full deinitialization of this variable.

The EMPTY_VALUE constant usually corresponds to the values of indicators that are not shown in the chart. For example, for built-in indicator Standard Deviation with a period of 20, the line for the first 19 bars in the history are not shown in the chart.

The CLR_NONE constant is used to outline the absence of color, it means that the graphical object or graphical series of an indicator will not be plotted. This constant was not included into the Web-color constants list, but it can be applied everywhere where the color arguments are required.

The INVALID_HANDLE constant can be used for checking file handles (see FileOpen() and FileFindFirst()).

The WRONG_VALUE constant is intended for cases, when it is necessary to return value of an enumeration, and this must be a wrong value. For example, when we need to inform that a return value is a value from this enumeration. Let's consider as an example some function CheckLineStyle(), which returns the line style for an object, specified by its name. If at style check by ObjectGetInteger() the result is true, a value from ENUM_LINE_STYLE is returned; otherwise WRONG_VALUE is returned.

void OnStart()
  {
   if(CheckLineStyle("MyChartObject")==WRONG_VALUE)
      printf("Error line style getting.");
  }
//+------------------------------------------------------------------+
//| returns the line style for an object specified by its name       |
//+------------------------------------------------------------------+
ENUM_LINE_STYLE CheckLineStyle(string name)
  {
   long style;
//---
   if(ObjectGetInteger(0,name,OBJPROP_STYLE,0,style))
      return((ENUM_LINE_STYLE)style);
   else
      return(WRONG_VALUE);
  }

The WHOLE_ARRAY constant is intended for functions that require specifying the number of elements in processed arrays:

If you want to specify that all the array values from a specified position till the end must be processed, you should specify just the WHOLE_ARRAY value.

IS_PROFILE_MODE constant allows changing a program operation for correct data collection in the profiling mode. Profiling allows measuring the execution time of the individual program fragments (usually comprising functions), as well as calculating the number of such calls. Sleep() function calls can be disabled to determine the execution time in the profiling mode, like in this example:

//--- Sleep can greatly affect (change) profiling result
if(!IS_PROFILE_MODE) Sleep(100); // disabling Sleep() call in the profiling mode

IS_PROFILE_MODE constant value is set by the compiler during the compilation, while it is set to zero in conventional mode. When launching a program in the profiling mode, a special compilation is performed and IS_PROFILE_MODE is replaced with a non-zero value.

The IS_DEBUG_MODE constant can be useful when you need to slightly change the operation of a mql4 program in the debugging mode. For example, in debug mode you may need to display additional debugging information in the terminal log or create additional graphical objects in a chart.

The following example creates a Label object and sets its description and color depending on the script running mode. In order to run a script in the debug mode from MetaEditor, press F5. If you run the script from the browser window in the terminal, then the color and text of the object Label will be different.

Example:

//+------------------------------------------------------------------+
//|                                             Check_DEBUG_MODE.mq5 |
//|                      Copyright © 2009, MetaQuotes Software Corp. |
//|                                        https://www.metaquotes.net |
//+------------------------------------------------------------------+
#property copyright "Copyright © 2009, MetaQuotes Software Corp."
#property link      "https://www.metaquotes.net"
//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
  {
//---
   string label_name="invisible_label";
   if(ObjectFind(0,label_name)<0)
     {
      Print("Object",label_name,"not found. Error code = ",GetLastError());
      //--- create Label
      ObjectCreate(0,label_name,OBJ_LABEL,0,0,0);
      //--- set X coordinate
      ObjectSetInteger(0,label_name,OBJPROP_XDISTANCE,200);
      //--- set Y coordinate
      ObjectSetInteger(0,label_name,OBJPROP_YDISTANCE,300);
      ResetLastError();
      if(IS_DEBUG_MODE) // debug mode
        {
         //--- show message about the script execution mode
         ObjectSetString(0,label_name,OBJPROP_TEXT,"DEBUG MODE");
         //--- set text color to red
         if(!ObjectSetInteger(0,label_name,OBJPROP_COLOR,clrRed))
            Print("Unable to set the color. Error",GetLastError());
        }
      else              // operation mode
        {
         ObjectSetString(0,label_name,OBJPROP_TEXT,"RELEASE MODE");
         //--- set text color to invisible
         if(!ObjectSetInteger(0,label_name,OBJPROP_COLOR,CLR_NONE))
            Print("Unable to set the color. Error ",GetLastError());
        }
      ChartRedraw();
      DebugBreak();    // here termination will occur, if we are in debug mode
     }
  }

Crypt Methods

The ENUM_CRYPT_METHOD enumeration is used to specify the data transformation method, used in CryptEncode() and CryptDecode() functions.

ENUM_CRYPT_METHOD

Constant	Description
CRYPT_BASE64	BASE64
CRYPT_AES128	AES encryption with 128 bit key (16 bytes)
CRYPT_AES256	AES encryption with 256 bit key (32 bytes)
CRYPT_DES	DES encryption with 56 bit key (7 bytes)
CRYPT_HASH_SHA1	SHA1 HASH calculation
CRYPT_HASH_SHA256	SHA256 HASH calculation
CRYPT_HASH_MD5	MD5 HASH calculation
CRYPT_ARCH_ZIP	ZIP archives