Setting a watch breakpoint

A watch breakpoint is a type of breakpoint that is triggered whenever execution changes data at a specific address. You use this type of breakpoint when you want to see where and how a variable is being changed in your program.

About this task

To set a watch breakpoint, do the following:

Procedure

  1. Right-click in the Breakpoints view and select Add Breakpoint > Watch from the pop-up menu. This will invoke the Add a Watch Breakpoint wizard, from which you will complete all other steps.

    Note: You can also open the Add a Watch Breakpoint wizard by right-clicking inside the editor and choosing Add Watch Breakpoint from the pop-up menu. This also works in the LPEX editor, but only if you are in a debug session already. Variables do not have an address if the program has not been started.

  2. In the Expression field, enter the name of the expression where the breakpoint is to be set. If you highlight a variable in the editor when you invoke the Add a Watch Breakpoint wizard, the Expression field of this dialog will be pre-filled with the variable.

    Applies to C Applies to C++ For C/C++, an expression is the name of a variable or any other expression that resolves to a storage address. For example, a dereferenced pointer is an expression.

  3. Enter the number of bytes of the address or expression you want to watch in the Number of bytes to watch field, or choose the number of bytes to watch from the field's drop-down menu. The expression will be evaluated and the result used as an address where the watch will start. The default value of this field is 0, which means that the entire length of the variable is watched.
  4. If you do not wish to set the frequency of the breakpoint, click Finish to set the breakpoint and dismiss the Add a Watch Breakpoint wizard.
  5. If you wish to set the frequency of the breakpoint, click Next >. In the resulting wizard page, you use the Frequency controls to tell the debugger when to stop on a breakpoint and when to skip it. The debugger keeps track of how many times each breakpoint is encountered. The fields in this section tell the debugger on which encounter of a breakpoint the debugger should first stop, how often it should stop, and on which encounter the debugger should no longer stop. The following parameters are used to set the breakpoint frequency:
    • From: Enter the first breakpoint encounter you want the debugger to stop on. For example, if you want the debugger to skip over the breakpoint the first five times it is encountered, enter "6".
    • To: Enter the last breakpoint encounter you want the debugger to stop on. For example, if you want it to start ignoring the breakpoint after the 20th encounter, enter "20". To have it always stop on the breakpoint, enter "Infinity".
    • Every: Enter the frequency with which you want the debugger to stop on this breakpoint. For example, if you want it to stop on only one out of every four it encounters, enter "4".
    Note: Other than the "Infinity" value, any frequency setting that you enter should be a numeric value. If you enter an alphabetic value, the debugger will use the default value for the field in which the alphabetic value was entered.

    When you are finished setting the frequency, click Finish to set the breakpoint and dismiss the Add a Watch Breakpoint wizard.

Results

In the Add a Watch Breakpoint wizard, all fields must be completed with valid entries before the breakpoint can be set. Note that the default frequency does not have to be changed.


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