MQL4 Reference Predefined Variables

The predefined Variables

For each executable mql4-program a set of predefined variables is supported, which reflect the state of the current price chart by the moment a mql4-program (Expert Advisor, script or custom indicator) is started.

Values of predefined variables are set by the client terminal before a mql4-program is started. Predefined variables are constant and cannot be changed from a mql4-program. As exception, there is a special variable _LastError, which can be reset to 0 by the ResetLastError function.

Variable	Value
_Digits	Number of decimal places
_Point	Size of the current symbol point in the quote currency
_LastError	The last error code
_Period	Timeframe of the current chart
_RandomSeed	Current status of the generator of pseudo-random integers
_StopFlag	Program stop flag
_Symbol	Symbol name of the current chart
_UninitReason	Uninitialization reason code
Ask	The latest known seller's price (ask price) of the current symbol
Bars	Number of bars in the current chart
Bid	The latest known buyer's price (offer price, bid price) of the current symbol
Close	Series array that contains close prices for each bar of the current chart
Digits	Number of digits after decimal point for the current symbol prices
High	Series array that contains the highest prices of each bar of the current chart
Low	Series array that contains the lowest prices of each bar of the current chart
Open	Series array that contains open prices of each bar of the current chart
Point	The current symbol point value in the quote currency
Time	Series array that contains open time of each bar of the current chart
Volume	Series array that contains tick volumes of each bar of the current chart

Predefined variables cannot be defined in a library. A library uses such variables that are defined in program from which this library is called.

Example:

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
  {
   Print("Symbol name of the current chart=",_Symbol);
   Print("Timeframe of the current chart=",_Period);
   Print("The latest known seller's price (ask price) for the current symbol=",Ask);
   Print("The latest known buyer's price (bid price) of the current symbol=",Bid);
   Print("Number of decimal places=",Digits);
   Print("Number of decimal places=",_Digits);
   Print("Size of the current symbol point in the quote currency=",_Point);
   Print("Size of the current symbol point in the quote currency=",Point);
   Print("Number of bars in the current chart=",Bars);
   Print("Open price of the current bar of the current chart=",Open[0]);
   Print("Close price of the current bar of the current chart=",Close[0]);
   Print("High price of the current bar of the current chart=",High[0]);
   Print("Low price of the current bar of the current chart=",Low[0]);
   Print("Time of the current bar of the current chart=",Time[0]);
   Print("Tick volume of the current bar of the current chart=",Volume[0]);
   Print("Last error code=",_LastError);
   Print("Random seed=",_RandomSeed);
   Print("Stop flag=",_StopFlag);
   Print("Uninitialization reason code=",_UninitReason);
  }

Operation of Programs in the Strategy Tester_Digits