Automated Trading Language Documentation

The predefined Variables

For each executable mql5-program a set of predefined variables is supported, which reflect the state of the current price chart by the moment a mql5-program (Expert Advisor, script or custom indicator) is started.

Values of predefined variables are set by the client terminal before a mql5-program is started. Predefined variables are constant and cannot be changed from a mql5-program. As exception, there is a special variable _LastError, which can be reset to 0 by the ResetLastError function.

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