$Common
The $COMMON directive provides a means for passing information from the Main program to Functions, Procedures, Modules, and Subprograms. Use of $COMMON provides an alternative to passing values as arguments. This directive is similar in concept to the COMMON statement in FORTRAN. It differs in that information flow is one-way. Variable values can be passed from the main program to the function, procedure or module. However, if the function, procedure or module changes the value of a variable in COMMON, the change will not be seen in the main program.
The $COMMON statement must directly follow the Function, Procedure, Module, and Subprogram declaration on a line by itself. Variables appearing in the $COMMON statement are separated with a space or with commas (or semicolons for the EU format) as in the following example.
FUNCTION TESTCOMMON(X)
$COMMON B,C,D {variables B,C, and D are from the main program}
TESTCOMMON:=X+B+C+D
END
B=4; C=5; D=6
G=TESTCOMMON(3)
$COMMON should only be used with Functions, Procedures, Modules, and Subprograms appearing in the Equations window. It should not be used with library functions. Array Range Notation (e.g., X[1..5] can be used in the $COMMON directive.
Note that complex variables can be passed to a Subprogram that is operating in the complex mode with a $Common directive.