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procedure_define_a_procedure_.htm
Navigation:  Language Reference > 2 - Program Source Code Format > Program Format >====== PROCEDURE (define a procedure) ====== Previous pageReturn to chapter overviewNext page
label PROCEDURE [ ( parameter list ) ]
local data
CODE
statements
[RETURN( [ value ] ) ]

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PROCEDURE Begins a section of source code that can be executed from within a PROGRAM.
label Names the PROCEDURE. For a CLASS method's definition, this may contain the label of the CLASS prepended to the label of the PROCEDURE.
parameter list A comma delimited list of names (and, optionally, their data types) of the parameters passed to the PROCEDURE. These names define the local references within the PROCEDURE to the passed parameters. For a CLASS method's definition, this may contain the label of the CLASS (named SELF) as an implicit first parameter (if the class is not prepended to the PROCEDURE's label), and must always contain both the data type and parameter name.
local data Declare Local data visible only in this procedure.
CODE Terminate the data declaration section and begin the executable code section of the PROCEDURE.
statements Executable program instructions.
RETURN Terminate procedure execution. Return to the point from which the procedure was called and return the value to the expression in which the procedure was used (if the procedure has been prototyped to return a value).
value A numeric or string constant or variable which specifies the result of the procedure call.

PROCEDURE begins a section of source code that can be executed from within a PROGRAM. It is called by naming the PROCEDURE label (with its parameter list, if any) as an executable statement in the code section of a PROGRAM or PROCEDURE.

The parameter list defines the data type of each parameter (optional) followed by the label of the parameter as used within the PROCEDURE's source code (required). Each parameter is separated by a comma. The data type of each parameter (including the angle brackets if the parameter is omittable) is required along with the parameter's label if the procedure is overloaded (has multiple definitions). The parameter list may be exactly the same as it appears in the PROCEDURE's prototype, if that prototype contains labels for the parameters.

A PROCEDURE may contain one or more ROUTINEs in its executable code statements. A ROUTINE is a section of executable code local to the PROCEDURE which is called with the DO statement.

A PROCEDURE terminates and returns to its caller when a RETURN statement executes. An implicit RETURN occurs at the end of the executable code. The end of executable code for the PROCEDURE is defined as the end of the source file, or the first encounter of a ROUTINE or another PROCEDURE.

A RETURN statement is required if the PROCEDURE has been prototyped to return a value. A PROCEDURE which has been prototyped to return a value can be used as an expression component, or passed as a parameter to another PROCEDURE. A PROCEDURE which has been prototyped to return a value may also be called in the same manner as a PROCEDURE without a RETURN value, if the program logic does not require the RETURN value. In this case, if the PROCEDURE prototype does not have the PROC attribute, the compiler will generate a warning which may be safely ignored.

Data declared within a PROCEDURE, between the keywords PROCEDURE and CODE, is Procedure Local data that can only be accessed by that PROCEDURE (unless passed as a parameter to another PROCEDURE). This data is allocated memory upon entering the procedure, and de-allocated when it terminates. If the data is smaller than the stack threshold (5K is the default) it is placed on the stack, otherwise it is allocated from the heap.

A PROCEDURE must have a prototype declared in a CLASS or the MAP of a PROGRAM or MEMBER module. If declared in the PROGRAM MAP, it is available to any other procedure in the program. If declared in a MEMBER MAP, it is available to other procedures in that MEMBER module.

Example:

PROGRAM                         !Example program code

MAP

OpenFile PROCEDURE(FILE AnyFile)!Procedure prototype with parameter

ShoTime   PROCEDURE              !Procedure prototype without parameter

DayString PROCEDURE,STRING       !Procedure prototype with a return value

END

FileOne FILE,DRIVER('Clarion')   !Declare a file

        RECORD                  !begin record declaration

Name      STRING(20)

Number    LONG

        END                     ! end record declaration

       END                      !End file declaration

TodayString STRING(9)

CODE

TodayString = DayString()      !Procedure called with a return value

OpenFile(FileOne)              !Call procedure to open file

ShoTime                        !Call ShoTime procedure

 !More executable statements

OpenFile PROCEDURE(FILE AnyFile)!Open any file

CODE                           !Begin code section

OPEN(AnyFile)                  !Open the file

IF ERRORCODE() = 2             !If file not found

 CREATE(AnyFile)               !create it

END  

RETURN                         !Return to caller

ShoTime PROCEDURE               !Show time

Time  LONG                      !Local variable

Window WINDOW,CENTER

       STRING(@T3),USE(Time),AT(34,70)

       BUTTON('Exit'),AT(138,92),USE(?Exit)

      END

CODE                           !Begin executable code section

Time = CLOCK()                 !Get time from system

OPEN(Window)

ACCEPT

 CASE ACCEPTED()

 OF ?Exit

  BREAK

 END

END

RETURN                         !Return to caller

DayString   PROCEDURE           !Day string procedure

ReturnString STRING(9),AUTO     !Uninitialized local stack variable

CODE                           !Begin executable code section

EXECUTE (TODAY() % 7) + 1      !Find day of week from system date

 ReturnString = 'Sunday'

 ReturnString = 'Monday'

 ReturnString = 'Tuesday'

 ReturnString = 'Wednesday'

 ReturnString = 'Thursday'

 ReturnString = 'Friday'

 ReturnString = 'Saturday'

END

RETURN(ReturnString)           !Return the resulting string

See Also:

PROCEDURE Prototypes

Data Declarations and Memory Allocation

Procedure Overloading

CLASS

ROUTINE

MAP

procedure_define_a_procedure_.htm.txt · Last modified: 2021/04/15 15:57 (external edit)