Add traces to programs

Before a traced statement processes, the value of the variable is recorded. Also, you can specify that the values of the variables are to be recorded only if they have changed from the last time a traced statement was processed. These variables can be displayed in character format or hexadecimal format.

To specify which statements are to be traced, you can specify:

• The statement identifier at which the trace is to start and the statement identifier at which the trace is to stop
• That all statements in the program are to be traced
• A single statement identifier of a statement to be traced

On the Start Debug (STRDBG) or Change Debug (CHGDBG) command, you can specify how many statement traces can be recorded for a job and what action the system should take when the maximum is reached. When the maximum is reached, the system performs one of the following actions (depending on what you specify):

• For an interactive job, either of the following can be done:
  • Stop the trace (*STOPTRC). Control is given to you (a breakpoint occurs), and you can remove some of the trace definitions (Remove Trace (RMVTRC) command), clear the trace data (Clear Trace Data (CLRTRCDTA) command), or change the maximum (MAXTRC parameter on the Change Debug (CHGDBG) command).
  • Continue the trace (*WRAP). Previously recorded trace data is overlaid with trace data recorded after this point.
• For a batch job, either of the following can be done:
  • Stop the trace (*STOPTRC). The trace definitions are removed and the program continues processing.
  • Continue the trace (*WRAP). Previously recorded trace data is overlaid with trace data recorded after this point.

You can change the maximum and the default action any time during the debug job using the Change Debug (CHGDBG) command. However, the change does not affect traces that have already been recorded.

You can only specify a total of five statement ranges for a single program at any one time, which is a total taken from all the Add Trace (ADDTRC) commands for the program. In addition, only 10 variables can be specified for each statement range.

In high-level language programs, different statements and labels may be mapped to the same internal instruction. This happens when there are several inoperable statements (such as DO, END) following one another in a program. You can use the IRP list to determine which statements or labels are mapped to the same instruction.

When you specify CL variables, you must enclose the & and the variable name in single apostrophes. For example:

ADDTRC PGMVAR('&IN01')

When you specify a statement range, the source statement number for the stop statement is ordinarily larger than the number for the start statement. Tracing, however, is performed with machine interface (MI) instructions, and some compilers (notably RPG/400^®) generate programs in which the order of MI instructions is not the same as the order of the source statements. Therefore, in some cases, the MI number of the stop statement may not be larger than the MI number of the start statement, and you will receive message CPF1982.

When you receive this message, you should do one of the following:

• Trace all statements in the program.
• Restrict a statement range to one specification.
• Use MI instruction numbers gotten from an intermediate representation of a program (IRP) list of the program.

The following Add Trace (ADDTRC) command adds a trace to the program CUS310. CUS310 is the default program, so it does not have to be specified. The value of the variable &TOTBAL is recorded only if its value changes between the times each traced statement is processed.

ADDTRC STMT((900 2700))  PGMVAR('&TOTBAL')  OUTVAR(*CHG)

The following displays result from this trace and are displayed using the Display Trace Data (DSPTRCDTA) command. Note that column headers are not supplied for all displays.

                            Display Trace Data
 
                 Statement/
Program          Instruction           Recursion level       
Sequence number
CUS310           900                          1              
             1
 
 Start position  . . . . . . . . . . . . :   1
 Length  . . . . . . . . . . . . . . . . :   *DCL
 Format  . . . . . . . . . . . . . . . . :   *CHAR
 
 Variable  . . . . . . . . . . . . . . . :   &TOTBAL
   Type  . . . . . . . . . . . . . . . . :     PACKED
   Length  . . . . . . . . . . . . . . . :     5 2
  '    .00'
 
                 Statement/
Program          Instruction           Recursion level       
Sequence number
CUS310           1000                         1              
             2
CUS310           1100                         1              
             3  +
 
Press Enter to continue.
 
F3=Exit   F12=Cancel
 

                            Display Trace Data
 
 
 Start position  . . . . . . . . . . . . :   1
 Length  . . . . . . . . . . . . . . . . :   *DCL
 Format  . . . . . . . . . . . . . . . . :   *CHAR
 
*Variable  . . . . . . . . . . . . . . . :   &TOTBAL
   Type  . . . . . . . . . . . . . . . . :     PACKED
   Length  . . . . . . . . . . . . . . . :     5 2
  '   1.00'
 
                 Statement/
Program          Instruction           Recursion level       
Sequence number
CUS310           1600                         1              
             4
CUS310           1700                         1              
             5
CUS310           2100                         1              
             6
CUS310           2200                         1              
             7
CUS310           2600                         1              
             8  +
 
Press Enter to continue.
 
F3=Exit   F12=Cancel
 

                            Display Trace Data
 
CUS310           2700                         1              
             9
 
 Start position  . . . . . . . . . . . . :   1
 Length  . . . . . . . . . . . . . . . . :   *DCL
 Format  . . . . . . . . . . . . . . . . :   *CHAR
 
*Variable  . . . . . . . . . . . . . . . :   &TOTBAL
   Type  . . . . . . . . . . . . . . . . :     PACKED
   Length  . . . . . . . . . . . . . . . :     5 2
  '   2.00'
 
 
 
 
 
 
 
 
Press Enter to continue.
 
F3=Exit   F12=Cancel