Recipe 13.9. Using a Breakpoint to Stop Execution of an Application When a Condition Is Met

Problem

You have some fairly complicated code that is having a problem after many iterations, and you need an easy way to stop execution when the conditions are met.

Solution

Set a conditional breakpoint using an expression in the Visual Studio debugger. The value of the expression will determine whether program execution breaks when the breakpoint is hit.

To set a conditional breakpoint in the Visual Studio debugger:

1. Set a breakpoint in the usual fashion by clicking in the gray border to the left of the line where you want execution to break.

2. Right-click the breakpoint and select the Condition command from the menu.

3. Use the Conditions dialog box to set the conditions for the break, as shown in Figure 13-5. Typically, you'll set a conditional expression like any of these:

    
    counter = 5000 i=100 AND j=150 message.Length > 0 
    counter == 5000 i==100 && j==150 message.Length > 0 

   
   

When you run the program, execution will break at the location when the expression is true or has changed, depending on the option you've chosen in the dialog box.

Discussion

You can view the contents of the Visual Studio Locals window to verify the values of the variables involved in the expression. Access the Locals window by selecting the Debug Windows Locals command; the Locals window is accessible only when the Visual Studio Debugger is active.

Figure 13-5. Setting a conditional breakpoint in Visual Studio

Another approach is to set a hit count by selecting the Hit Count command from the menu. The hit count lets you specify how many times the breakpoint is hit before the debugger enters break mode. For example, you might choose to break when the hit count is equal to 100. The debugger will break only when the hit count reaches the target number.

See Also

All the rules for setting breakpoint expressions are available from Visual Studio Help under the "Expressions in the Debugger" topic, which is accessible from the Breakpoint Properties dialog box (the expression evaluator accepts most expressions written in Visual Basic or C#).