CL Programming
While each source statement entered as part of a CL procedure is actually a
CL command, the source can be divided into the following basic parts used in
many typical CL procedures.
- PGM command
- PGM PARM(&A)
Optional PGM command beginning the procedure and identifying any parameters
received.
- Declare commands
- (DCL, DCLF)
Mandatory declaration of procedure variables when variables are
used. The declare commands must precede all other commands except the
PGM command.
- CL processing commands
- CHGVAR, SNDPGMMSG, OVRDBF, DLTF, ...
CL commands used as source statements to manipulate constants or variables
(this is a partial list).
- Logic control commands
- IF, THEN, ELSE, DO, ENDDO, GOTO
Commands used to control processing within the CL procedure.
- Built-in functions
- %SUBSTRING (%SST), %SWITCH, and %BINARY (%BIN)
Built-in functions and operators used in arithmetic, relational or logical
expressions.
- Program control commands
- CALL, RETURN
CL commands used to pass control to other programs.
- Procedure control commands
- CALLPRC, RETURN
CL commands used to pass control to other procedures.
- ENDPGM command
- ENDPGM
Optional End Program command.
The sequence, combination, and extent of these components are determined by
the logic and design of your application.
A CL procedure may refer to other objects that must exist when the
procedure is created, when the command is processed, or both. This
distinction is discussed in Accessing Objects in CL Programs, and in the sections discussing various objects. In
some circumstances, for your procedure to run successfully, you may
need:
- A display file. Use display files to format information on a device
display. If your procedure uses a display, you must enter and create
the display file and record format by using the Create Display File (CRTDSPF)
command before creating the module. You must declare it to the
procedure in the DCL section by using the Declare File (DCLF) command.
See Working with Files in CL Procedures for more information.
- A database file. Records in a database file may be read by a CL
procedure. If your procedure uses a database file, the file must be
created using the Create Physical File (CRTPF) command or the Create Logical
File (CRTLF) command before the module is created. You can use Data
Description Specifications (DDS), Structured Query Language (SQL), or
interactive data definition utility (IDDU) to define the format of the records
in the file. The file must also be declared to the procedure in the DCL
section using the Declare File (DCLF) command. See Working with Files in CL Procedures for more information.
- Other programs. If you use a CALL command, the called program must
exist before running the CALL command. It does not have to exist when
compiling the calling module. See Accessing Objects in CL Programs and "Controlling Flow and Communicating between Programs and Procedures" for more information.
- Other procedures. If you use the CALLPRC command, the called
procedure must exist at the time CRTPGM is run. It does not have to
exist when CRTCLMOD is run.
[ Top of Page | Previous Page | Next Page | Table of Contents | Index ]
(C) Copyright IBM Corporation 1992, 2005. All Rights Reserved.