Double-click the line in the Source window.The Data menu provides commands to add and delete watch expressions and breakpoints. Watch expressions allow you to observe how variables change as your program executes and also to expand arrays and dereference pointers. Breakpoints allow you to stop execution of your program to check the values of your variables, determine execution flow, and change how your program executes.
For more information about watch expressions, see Chapter 11, “Using Expressions in CodeView” and the “Add Watch Expression” command on page 460.
The following table summarizes the commands on the Data menu:
| Command | Purpose |
| Add Watch | Adds an expression to the Watch window |
| Delete Watch | Deletes an expression from the Watch window |
| Set Breakpoint | Sets a breakpoint in the program |
| Edit Breakpoints | Modifies or removes existing breakpoints |
| Quick Watch | Displays a quick view of a variable or expression |
The Add Watch command (CTRL+W) displays the Add Watch dialog box, which shows the selected text or the word at the cursor in the Expression text box. You can enter a different expression or add a format specifier to the expression. When you choose OK, the expression is added to the end of the Watch window.
The Delete Watch command (CTRL+U) displays the Delete Watch dialog box, which displays a list of the watch expressions in the Watch window. Select the expression you want to delete from the list and choose OK. Click the Clear All button to remove all expressions from the Watch window.
You can also delete expressions directly from the Watch window. Use the mouse or the cursor keys to move the cursor to the expression you want removed, and press CTRL+Y.
The Set Breakpoint command displays the Set Breakpoint dialog box, which allows you to select from several kinds of breakpoints and set options for each type. The following list describes the breakpoints you can set:
Break at Location
This is the simplest type of breakpoint. You specify an address or a line number where you want execution to pause. To specify a line number, precede it with a period (.); otherwise, CodeView will interpret it as an address. When your program's execution reaches the breakpoint location, your program stops temporarily, and you can enter CodeView commands.
Break at Location if Expression is True
You specify a location and an expression. Whenever execution reaches that location, CodeView checks the expression. If the expression is true (nonzero), the breakpoint is taken. Otherwise, execution continues.
Break at Location if Expression has Changed
You specify a location and an expression that represents a variable or any portion of memory. To specify a range of memory, enter the length of the range in the Length text box. CodeView checks the variable or the range of memory when execution reaches the breakpoint location. If the value of any byte has changed since the last time CodeView checked, the breakpoint is taken. Otherwise, execution continues.
Break When Expression is True
This breakpoint is taken whenever the expression becomes true. CodeView evaluates the expression after every line or every instruction, instead of only at a certain location. As a result, this type of breakpoint can greatly slow your program's execution.
Break When Expression has Changed
CodeView checks the variable or the range of memory as each line or each instruction is executed. You can also specify a range with the Length text box. This type of breakpoint can also slow your program's execution.
Each breakpoint is numbered, beginning with 0. For each type of breakpoint, you can set several options. If you try to use an option that does not apply to a certain breakpoint, CodeView displays N/A in the edit box and ignores that option. The options are:
Location
Specifies where CodeView should evaluate the breakpoint.
Expression
Specifies an expression that causes a break when it becomes true or a location that is to be watched for changes.
Length
Specifies a range of memory (starting at the address in the Expression text box) to watch for changes.
Pass Count
Specifies the number of times to pass over the breakpoint when it otherwise would be taken. For example, a pass count of 10 tells CodeView to ignore the breakpoint ten times.
Commands
Specifies a list of Command-window commands, separated by semicolons, that are executed when the breakpoint is taken. If several breakpoints with commands are taken, the commands are queued and executed in first-in, first-out order.
As shortcuts, you can also set simple (break at location) breakpoints with the following methods:
Double-click the line in the Source window.
Move the cursor to the breakpoint location in the Source window and press F9.
A line with a breakpoint is highlighted. In the Mixed and Assembly modes, an assembly-language comment that displays the breakpoint number appears. For example:
0047:0b30 57 push di ;BK0
In this example, breakpoint number 0 is set at the address 0047:0B30.
You can also set breakpoints with the Breakpoint Set (BP) command. See the “Breakpoint Set” command on page 429.
The Edit Breakpoints command displays the Edit Breakpoints dialog box, where you can add, remove, change, enable, and disable breakpoints. Select a breakpoint from the list of breakpoints, then choose one of the command buttons on the right side of the dialog box.
The list of breakpoints in the Edit Breakpoints dialog box shows the current state of each breakpoint in your program. For more information on the format of the breakpoint list, see the “Breakpoint List” command on page 429.
The command buttons in the Edit Breakpoints dialog box are described in the following table:
| Button | Description |
| Add | Adds a new breakpoint |
| Remove | Removes the selected breakpoint |
| Modify | Modifies the same breakpoint |
| Enable | Activates a disabled breakpoint |
| Disable | Disables an active breakpoint |
| Clear All | Removes all breakpoints |
If you select the Modify button, CodeView displays the Set Breakpoint dialog box with the appropriate options set for the breakpoint you selected. You can then modify the options and set the breakpoint just as you do with the Set Breakpoint command.
When you disable a breakpoint by selecting the Disable button, CodeView does not evaluate the breakpoint. Program execution continues as if the breakpoint was never set.
You may encounter several occasions where it is useful to disable a breakpoint. Sometimes a certain breakpoint is not practical when you are debugging a routine nested deeply in your program. You can reenable the breakpoint later when you really need it. Also, conditional breakpoints are evaluated at every program step and can slow execution. You can disable some conditional breakpoints in areas of your program where you're certain you won't need them.
The Quick Watch command (SHIFT+F9) displays the Quick Watch dialog box, which shows the variable at the cursor position or the selected expression. The Quick Watch dialog box is similar to the Watch window. However, you mainly use Quick Watch for a quick exploration of the current values in an array or a pointer-based data structure, rather than as a method to constantly display the values.
The Quick Watch dialog box automatically expands structures, arrays, and pointers to their first level. You can expand or contract an element just as you can in the Watch window. If the expanded item needs more lines than the Quick Watch dialog box can display, you can scroll the view up and down.
Choose the Add Watch button to add a Quick Watch item to the Watch window. Expanded items appear in the Watch window as they are displayed in the Quick Watch dialog box.
For complete information on using the Quick Watch dialog box, see the “Quick Watch” command on page 478.