PARAM_PRESENT Function

Tests if a parameter was actually present in the call to a procedure or function.

result = PARAM_PRESENT(parameter)

parameter One of the formal parameters as given in the function or procedure definition.

result A nonzero value (true) if the parameter was present in the call to the current procedure or function. Returns a zero value (false) if the parameter was not present.

None.

PARAM_PRESENT compliments the KEYWORD_SET and N_ELEMENTS functions. PARAM_PRESENT lets you distinguish between the two cases in which KEYWORD_SET returns FALSE, and the two cases when N_ELEMENTS returns zero (0).

The KEYWORD_SET function returns FALSE:

1) When the keyword was set to zero or an undefined variable.

2) When the keyword was not used in the call.

PARAM_PRESENT distinguishes between these cases by returning TRUE in case 1 and FALSE in case 2.

The N_ELEMENTS function returns zero (0) in two cases;

1) When the keyword or parameter was present but is an undefined variable.

2) When the keyword or parameter was not present in the call.

PARAM_PRESENT distinguishes between these two cases by returning TRUE in case 1 and FALSE in case 2.

The following example demonstrates the expected results when the functions PARAM_PRESENT, KEYWORD_SET, and N_ELEMENTS are used in a procedure.

PRO test, Key = k

IF (PARAM_PRESENT(k)) THEN $
    PRINT, 'Key is present' $
ELSE PRINT, 'Key is not present'
IF (KEYWORD_SET(k)) THEN $
    PRINT, 'Key is set' $
    ELSE PRINT, 'Key is NOT SET'
PRINT, 'Number of elements in Key = ', N_ELEMENTS(k)

END
WAVE test

Key is not present
Key is NOT SET
Number of elements in Key = 0

WAVE test, Key = 0

Key is present
Key is NOT SET
Number of elements in key = 1

WAVE test, Key = a

Key is present
Key is NOT SET
Number of elements in key = 0

WAVE a = 10
WAVE test, Key = a

Key is present
Key is SET
Number of elements in Key = 1

KEYWORD_SET, N_ELEMENTS, N_PARAMS

For more information on parameter checking, see Hardware-dependent Math Error Handling in Chapter 10 of the PV-WAVE Programmer's Guide.