6.9 Debugging programs

To debug a program, it must be compiled with debug information. Compiling a program with debug information allows to:

1. Execute the program line by line.
2. Run the program till a certain point (a breakpoint)
3. Inspect the contents of variables or memory locations while the program is running.

Using breakpoints

To set a breakpoint on the current source line, use the ”Debug--Breakpoint” menu entry, or press CTRL-F8.

A list of current breakpoints can be obtained through the ”Debug--Breakpoint list” menu. The breakpoint list window is shown in figure (6.11).

In the breakpoint list window, the following things can be done:

New

Shows the breakpoint property dialog where the properties for a new breakpoint can be entered.

Edit

Shows the breakpoint property dialog where the properties of the highlighted breakpoint can be changed.

Delete

Deletes the highlighted breakpoint.

The dialog can be closed with the ’Close’ button. The breakpoint properties dialog is shown in figure (6.12)

The following properties can be set:

type

function

function breakpoint. The program will stop when the function with the given name is reached.

file-line

Source line breakpoint. The program will stop when the source file with given name and line is reached;

watch

Expression breakpoint. An expression may be entered, and the program will stop as soon as the expression changes.

awatch

(access watch) Expression breakpoint. An expression that references a memory location may be entered, and the program will stop as soon as the memory indicated by the expression is accessed.

rwatch

(read watch) Expression breakpoint. An expression that references a memory location may be entered, and the program will stop as soon as the memory indicated by the expression is read.

name

Name of the function or file where to stop.

line

Line number in the file where to stop. Only for breakpoints of type file-line.

Conditions

Here an expression can be entered which must evaluate True for the program to stop at the breakpoint. The expressions that can be entered must be valid GDB expressions.

Ignore count

The number of times the breakpoint will be ignored before the program stops;

Remark:

1. Because the IDE uses GDB to do its debugging, it is necessary to enter all expressions in uppercase on FREEBSD.
2. Expressions that reference memory locations should be no longer than 16 bytes on LINUX or go32v2 on an Intel processor, since the Intel processor’s debug registers are used to monitor these locations.
3. Memory location watches will not function on Win32 unless a special patch is applied.

Using watches

Setting a new watch can be done with the ”Debug--Add watch” menu command or by pressing CTRL-F7. When this is done, the watch property dialog appears, and a new expression can be entered. The watch property dialog is shown in figure (6.13).

In the dialog, the expression can be entered, any possible previous value and current value are shown.

Remark: Because the IDE uses GDB to do it’s debugging, it is necessary to enter all expressions in uppercase in FREEBSD. A list of watches and their present value is available in the watches window, which can be opened with the ”Debug--Watches” menu. The watch list window is shown in figure (6.11).

Pressing ENTER or the space bar will show the watch property dialog for the currently highlighted watch in the watches window.

The list of watches is updated whenever the IDE resumes control when debugging a program.

The call stack

By pressing the space bar in the call stack window, the line corresponding to the call will be highlighted in the edit window.

The GDB window

Some more information on using GDB can be found in section 10.2, page 349, but the final reference is of course the GDB manual itself ³. The GDB window is shown in figure (6.16).