Debugging is a crucial skill for any programmer, and Control Language (CL) is no exception. This section will cover various techniques and tools available for debugging CL programs. By the end of this module, you should be able to identify and fix errors in your CL scripts efficiently.

1. Understanding Debugging: The process of identifying, analyzing, and removing errors (bugs) from a program.
2. Types of Errors:
   • Syntax Errors: Mistakes in the code that prevent the program from running.
   • Runtime Errors: Errors that occur while the program is running.
   • Logical Errors: Errors in the logic of the program that produce incorrect results.

The DSPJOBLOG (Display Job Log) command is one of the most useful tools for debugging CL programs. It displays the job log, which contains messages about the job's execution, including errors and warnings.

Example:

Explanation:

• JOB(123456/QUSER/MYJOB): Specifies the job identifier. Replace with your job's identifier.

The SNDPGMMSG (Send Program Message) command allows you to send messages to the job log or a message queue. This is useful for tracking the flow of your program and the values of variables at different points.

Example:

Explanation:

• DCL VAR(&MYVAR) TYPE(*CHAR) LEN(10): Declares a variable &MYVAR of type character with a length of 10.
• CHGVAR VAR(&MYVAR) VALUE('Hello'): Changes the value of &MYVAR to 'Hello'.
• SNDPGMMSG MSG('Value of &MYVAR is ' *CAT &MYVAR): Sends a message to the job log with the value of &MYVAR.

The STRDBG (Start Debug) command allows you to set breakpoints in your CL program. When the program reaches a breakpoint, it pauses execution, allowing you to inspect variables and step through the code.

Example:

Explanation:

• PGM(MYLIB/MYPGM): Specifies the program to debug. Replace MYLIB with your library and MYPGM with your program name.

The STRISDB (Start Interactive Source Debugger) command provides an interactive debugging environment where you can set breakpoints, watch variables, and step through the code.

Example:

Explanation:

• PGM(MYLIB/MYPGM): Specifies the program to debug. Replace MYLIB with your library and MYPGM with your program name.

Task:

1. Write a CL program that declares a variable, changes its value, and sends a message with the variable's value.
2. Introduce a syntax error and a logical error.
3. Use the DSPJOBLOG, SNDPGMMSG, and STRDBG commands to identify and fix the errors.

Solution:

Step 1: Write the CL Program

Step 2: Introduce Errors

• Syntax Error: Misspell CHGVAR as CHGVR.
• Logical Error: Change the value of &MYVAR to 'World' instead of 'Hello'.

Step 3: Debug the Program

• Run the program and use DSPJOBLOG to identify the syntax error.
• Fix the syntax error and re-run the program.
• Use SNDPGMMSG to add debugging messages and identify the logical error.
• Use STRDBG to set breakpoints and step through the code to ensure the logic is correct.

• Common Mistake: Ignoring the job log.
  • Tip: Always check the job log for error messages and warnings.
• Common Mistake: Not using debugging messages.
  • Tip: Use SNDPGMMSG liberally to track the flow of your program and the values of variables.
• Common Mistake: Overlooking logical errors.
  • Tip: Use breakpoints and step through your code to ensure the logic is correct.

In this section, we covered various debugging techniques and tools available for CL programs. By using commands like DSPJOBLOG, SNDPGMMSG, STRDBG, and STRISDB, you can efficiently identify and fix errors in your CL scripts. Practice these techniques to become proficient in debugging and ensure your programs run smoothly.

Next, we will delve into performance optimization techniques to make your CL programs run more efficiently.