Predefined variables

Each MQL program has a certain general set of global variables provided by the terminal: we have already covered most of them in the previous sections, and below is a summary table. Almost all variables are read-only. The exception is the variable _LastError, which can be reset by the ResetLastError function.

Variable	Value
_LastError	Last error value, an analog of the GetLastError function
_StopFlag	Program stop flag, an analog of the IsStopped function
_UninitReason	Program deinitialization reason code, an analog of the UninitializeReason function
_RandomSeed	Current internal state of the pseudo-random integer generator
_IsX64	Flag of a 64-bit terminal, analog of TerminalInfoInteger for the TERMINAL_X64 property

In addition, for MQL programs running in the chart context of a chart, such as Expert Advisors, scripts, and indicators, the language provides predefined variables with chart properties (they also cannot be changed from the program).

Variable	Value
_Symbol	Name of the current chart symbol, an analog of the Symbol function
_Period	Current chart timeframe, an analog of the Period function
_Digits	The number of decimal places in the price of the current chart symbol, an analog of the Digits function
_Point	Point size in the prices of the current symbol (in the quote currency), an analog of the Point function
_AppliedTo	Type of data on which the indicator is calculated (only for indicators)

Debug management

Predefined constants of the MQL5 language