DO

DO*

Call a procedure

Syntax

      DO <idProcedure> [WITH <argument list>]

Arguments

<idProcedure> is the name of the procedure or user-defined function to be executed.

WITH <argument list> specifies up to 128 arguments, separated by commas, to pass to <idProcedure>. Each argument may be a single variable, field, array, array element, expression, or object. Arguments can be skipped or left off the end of the list.

Description

The DO statement calls a procedure or user-defined function, optionally passing arguments to the called routine. It performs the same action as a user-defined function or procedure specified on a line by itself with the exception that variables other than field variables are passed by reference as the default. In order to pass a field variable as an argument, enclose it in parentheses, unless you declare it with the FIELD statement or with an alias.

The number of specified arguments need not match the number of specified parameters in the called procedure. If the number of arguments is less than the number of parameters, the parameter variables with no corresponding arguments are initialized with a NIL value when the procedure is called. If the number of arguments is greater than the number of parameters, they are ignored.

Also, skipping an argument within the <argument list> by leaving an empty spot next to the comma initializes the corresponding argument to NIL. To detect the position of the last argument passed in the <argument list>, use PCOUNT(). To detect a skipped argument, compare the receiving parameter to NIL.

In addition to calling a procedure or user-defined function, DO also has an effect on compilation if you compile the current program file without the /M option. If the compiler encounters a DO statement and the specified procedure has not already been compiled, the compiler searches the current directory for a .prg file with the same name and compiles it. If the file with the same name as the procedure is not found, the called procedure is assumed to be external, and a reference is added to the object (.OBJ) file. At link time, the linker will search other object files and libraries for this external reference.

DO is a compatibility statement and therefore not recommended. Calling a procedure or function on a line by itself is the preferred method. Since this preferred calling convention normally passes parameters by value, you must preface an argument with the pass- by-reference operator (@) in order to pass by reference. If you are using DO to make a procedure call more readable, a user-defined command, specified with the #command directive, can provide greater readability without sacrificing the safety of variables passed as parameters. For more information on passing parameters refer to the Functions and Procedures section of the “Basic Concepts”.

Examples

       .  This example executes a procedure with no parameters:
          DO AcctsRpt
          AcctsRpt()                           // Preferred method
       .  This example executes a procedure passing two constants:
          DO QtrRpt WITH "2nd", "Sales Division"
          QtrRpt("2nd", "Sales Division")      // Preferred method
       .  In this example, a procedure is executed with the first
          argument passed by value and the second passed by reference:
          nNumber := 12
          DO YearRpt WITH nNumber + 12, nNumber
          YearRpt(nNumber + 12, @nNumber)      // Preferred method
       .  Here, a procedure is invoked with skipped arguments embedded
          in the list of arguments:
          DO DisplayWindow WITH ,,,,"My Window"
          DisplayWindow(,,,,"My Window")       // Preferred method

Seealso

FUNCTION, LOCAL, PARAMETERS, PRIVATE, PROCEDURE, PUBLIC

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One response to “DO

  1. Pingback: Harbour Statements | Viva Clipper !

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