Use Place-Holder Commas in Calls with Missing Parameters

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

This article shows by example how to pass parameters to functions, procedures, or methods by using place-holder commas for empty values that will take a default value. When you pass nothing, the function receives false (.F.) as the value for that argument.

This Visual FoxPro behavior is different from the behavior of FoxPro version 2.6. In FoxPro version 2.6, you could pass fewer arguments than total number of parameters only if the blank arguments came after the valid (full) arguments.

MORE INFORMATION

In Visual FoxPro version 3.0, you can pass fewer arguments than are requested by a function, method, or procedure by using place-holder commas when you call it.

Code Sample

To demonstrate passing blank parameters, copy the following code into a program file called FOXTEST.PRG and run it:

   *** BEGINNING OF SAMPLE CODE ***

   *****************************************************************
   *                         FOXTEST.PRG                           *
   *   Demonstrates How Visual FoxPro Allows Passing Blank Values  *
   *         For Parameters Anywhere In the Parameter List         *
   *                                                               *
   *****************************************************************

   SomeDate = mydate(3,4,95) && Pass values for all parameters
   WAIT WINDOW SomeDate

   SomeDate = mydate(4,,94) && Pass blank values for 2nd parameter
   WAIT WINDOW SomeDate

   SomeDate = mydate(,4,)   && Pass blank values for 1st and 3rd
   WAIT WINDOW SomeDate     && parameters

   SomeDate = mydate(,,94)  && Pass blank values for 1st and 2nd
   WAIT WINDOW SomeDate     && parameters

   SomeDate = mydate(4,,)   && Pass blank values for 2nd and 3rd
   WAIT WINDOW SomeDate     && parameters (This is the only way FoxPro
                            && 2.x allowed blank values to be passed,
                            && at the end of the parameter list only.)

   PROCEDURE MyDate
   PARAMETERS Month,Day,Year

   * Give each variable a default value for the missing parameters.

   DO CASE
      CASE TYPE("Day")="L"
         lcday="01"
      CASE TYPE("Day")="N"
         lcday=ALLTRIM(STR(DAY))
   ENDCASE

   DO CASE
      CASE TYPE("Year")="L"
         lcyear="95"
      CASE TYPE("Year")="N"
         lcyear=ALLTRIM(STR(Year))
   ENDCASE

   DO CASE
      CASE TYPE("Month")="L"
         lcmonth="01"
      CASE TYPE("Month")="N"
         lcmonth=ALLTRIM(STR(Month))
   ENDCASE

   RETURN lcmonth+"/"+lcday+"/"+lcyear

   *** End Of Sample Code ***

REFERENCES

For more information about passing parameters in a parameter list, refer to the Visual FoxPro Help file, "Parameters Command" topic.