KEYWORD_SET Function

Tests if an input expression has a nonzero value.

result = KEYWORD_SET(expr)

expr The expression to be tested. Usually a named variable.

result A nonzero value, if expr is defined and nonzero.

None.

KEYWORD_SET is especially useful in user-written procedures and functions when you want to process keywords that can be interpreted as being either true (keyword is present and nonzero) or false (keyword was not used, or was set to zero).

It can also be used to test whether an expression evaluates to zero, or whether a variable has been set.

Assume you type the following commands:

IF KEYWORD_SET(x) THEN PRINT, 'It is set' ELSE PRINT, 'Not set'

You will see:

Not set

because the value of x has not been initialized. On the other hand, if you set x to a specific value, say 2, you will see:

x = 2
IF KEYWORD_SET(x) THEN PRINT, 'It is set' ELSE PRINT, 'Not set'
It is set

The following user-defined routine uses KEYWORD_SET to make a call to print the results of a squaring operation:

FUNCTION SQUARE_IT, Value, Print_Flag = Print

Squared_Val = Value * Value
IF (KEYWORD_SET(Print)) THEN PRINT, Squared_Val
RETURN, Squared_Val

END

To run this routine, enter the following commands at the WAVE prompt:

.RUN SQUARE_IT.PRO
y = SQUARE_IT(5) 
PRINT, y

y = SQUARE_IT(10, /Print_Flag)

N_ELEMENTS, N_PARAMS, PARAM_PRESENT