Is there a way to place a watch on variable and only have Visual Studio break when that value changes?
It would make it so much easier to find tricky state issues.
Can this be done?
Breakpoint conditions still need a breakpoint set, and I'd rather set a watch and let Visual Studio set the breakpoints at state changes.
In the Visual Studio 2005 menu:
Debug -> New Breakpoint -> New Data Breakpoint
Enter:
&myVariable
You can also choose to break explicitly in code:
// Assuming C#
if (condition)
{
System.Diagnostics.Debugger.Break();
}
From MSDN:
Debugger.Break: If no debugger is attached, users are asked if they want to attach a debugger. If yes, the debugger is started. If a debugger is attached, the debugger is signaled with a user breakpoint event, and the debugger suspends execution of the process just as if a debugger breakpoint had been hit.
This is only a fallback, though. Setting a conditional breakpoint in Visual Studio, as described in other comments, is a better choice.
Update in 2019:
This is now officially supported in Visual Studio 2019 Preview 2 for .Net Core 3.0 or higher. Of course, you may have to put some thoughts in potential risks of using a Preview version of IDE. I imagine in the near future this will be included in the official Visual Studio.
Fortunately, data breakpoints are no longer a C++ exclusive because they are now available for .NET Core (3.0 or higher) in Visual Studio 2019 Preview 2!
I remember the way you described it using Visual Basic 6.0. In Visual Studio, the only way I have found so far is by specifying a breakpoint condition.
Right click on the breakpoint works fine for me (though mostly I am using it for conditional breakpoints on specific variable values. Even breaking on expressions involving a thread name works which is very useful if you're trying to spot threading issues).
As Peter Mortensen wrote:
In the Visual Studio 2005 menu:
Debug -> New Breakpoint -> New Data Breakpoint
Enter: &myVariable
Additional information:
Obviously, the system must know which address in memory to watch.
So
- set a normal breakpoint to the initialisation of myVariable (or myClass.m_Variable)
- run the system and wait till it stops at that breakpoint.
- Now the Menu entry is enabled, and you can watch the variable by entering &myVariable,
or the instance by entering &myClass.m_Variable. Now the addresses are well defined.
Sorry when I did things wrong by explaining an already given solution. But I could not add a comment, and there has been some comments regarding this.
You can use a memory watchpoint in unmanaged code. Not sure if these are available in managed code though.