Using IBM Application Development Tools for z/OS and OS/390

Chapter 17. Debug Tool and debugging C/C++ 361

17.2 Using the MFI debugger

Next we present the steps to using the MFI debugger:

1. The first step for using the main frame interface (MFI) is to invoke the program from batch

using the appropriate test runtime option. We will be debugging the C IVP that was

already compiled. The C IVP program can run with any number of command line

parameters. For our initial run, we will go with no parameters.

It may be to your advantage to allocate an INSPLOG data set. This will allow the setup

commands from this run to be captured, edited, and used as a preferences file for the next

run of this program. Remember that log data sets must be sequential and FB 72. We also

have had success with using the PC’s cut and paste feature to cut the commands we like

from the log screen of the debugger in order to create a preferences file.

For our purposes, the default LE values for the first three parameters are sufficient. But we

will not be using an INSPPREF file. Figure 17-1 shows the resultant command.

Figure 17-1 Invoking Debug Tool for the C IVP program

2. On entry to Debug Tool, the MFI screen looks as shown in Figure 17-2.

Figure 17-2 The MFI Screen on entry to C IVP

3. Now, we want to stop at the call to printf and at the exit. So we issue the commands:

AT CALL printf;

AT EXIT main;

362 Using IBM Application Development Tools for z/OS and OS/390

And we want to monitor i from the beginning and stop at main so we can monitor the

parameters to main:

MONITOR LIST i;

AT ENTRY main;

Pressing Enter produces the panel shown in Figure 17-3.

Figure 17-3 Debug Tool MFI screen after initial commands

4. If we press PF 11 to zoom to the log file, the panel in Figure 17-4 is displayed.

Figure 17-4 A zoom look at the log file after our initial commands

Chapter 17. Debug Tool and debugging C/C++ 363

5. Pressing PF11 gets us back to the original view. At this point we run the program and wait

for the first breakpoint to be reached, as shown in Figure 17-5.

Figure 17-5 At the first breakpoint

In Figure 17-5, note that the location where Debug Tool has stopped appears at the top

line of the screen.

6. At this point we want to add additional monitor statements for ac, av, and *av. Ideally one

should be able to put these monitor statements in one entry, but some experimentation

has found that they are not always accepted when the variable is out of scope. For this

reason we recommend putting a breakpoint at the appropriate scope and turning on the

monitoring at that point. The new monitor commands are:

MONITOR LIST ac;

MONITOR LIST av;

MONITOR LIST *av;

The monitor section at the top of Figure 17-6 now has entries for i, ac, av, and *av.

364 Using IBM Application Development Tools for z/OS and OS/390

Figure 17-6 At entry of main monitors showing initial values

7. Zooming to the log, we now find a summary of all our setup commands as shown in

Figure 17-7.

Figure 17-7 Current log file after all commands are set up

If you did not set up an INSPLOG this would be a good time to cut the commands from the

log file to later create a preference file.

Chapter 17. Debug Tool and debugging C/C++ 365

8. Press PF 11 to get back to the original view.

9. At this point we run again and the panel in Figure 17-8 is displayed.

Figure 17-8 At the exit of the program

Note that the printf breakpoint was never triggered because the printf was never executed.

Typ e qq to quit this session.

10.Edit your INSPLOG to create a preference file or paste the value cut from the log above.

Remember that a preference file should be FB 80

without sequence numbers. Our

preference file looks as shown in Figure 17-9.

Figure 17-9 Our new preferences file