Break when a value changes using the Visual Studio debugger

Question

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

User · Answer

You can use a memory watchpoint in unmanaged code  Not sure if these are available in managed code though

User · Answer

Change the variable into a property and add a breakpoint in the set method  Example   private bool m Var   false  protected bool var       get            return m var             set            m var   value

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If you are using WPF  there is an awesome tool   WPF Inspector  It attaches itself to a WPF app and display the full tree of controls with the all properties  an it allows you  amongst other things  to break on any property change   But sadly I didn t find any tool that would allow you to do the same with ANY property or variable

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You can optionally overload the   operator for the variable and can put the breakpoint inside the overloaded function on specific condition

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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

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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

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Really old post but in case someone is unaware     In Visual Studio 2015  you can place a breakpoint on the set accessor of an Auto-Implemented Property and the debugger will break when the property is updated  public bool IsUpdated       get      set       set breakpoint on this line     Update  Alternatively   AbdulRaufMujahid has pointed out in the comments that if the auto implemented property is on a single line  you can position your cursor at the get  or set  and hit F9 and a breakpoint will be placed accordingly  Nice   public bool IsUpdated   get  set

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Imagine you have a class called A with the following declaration   class A           public            A         private          int m value       You want the program to stop when someone modifies the value of  m value    Go to the class definition and put a breakpoint in the constructor of A   A  A                set breakpoint here     Once we stopped the program   Debug -  New Breakpoint -  New Data Breakpoint      Address   amp  this- m value  Byte Count  4  Because int has 4 bytes   Now  we can resume the program  The debugger will stop when the value is changed   You can do the same with inherited classes or compound classes   class B      private         A m a       Address   amp  this- m a m value   If you don t know the number of bytes of the variable you want to inspect  you can use the sizeof operator   For example      to know the size of the word processor       if you want to inspect a pointer  int wordTam   sizeof  void        If you look at the  Call stack  you can see the function that changed the value of the variable

User · Answer

As Peter Mortensen wrote      In the Visual Studio 2005 menu       Debug -  New Breakpoint -  New Data Breakpoint      Enter   amp 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  amp myVariable  or the instance by entering  amp 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

User · Answer

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

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You can probably make a clever use of the DebugBreak   function

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In the Visual Studio 2005 menu   Debug -  New Breakpoint -  New Data Breakpoint  Enter    amp myVariable

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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   https   blogs msdn microsoft com visualstudio 2019 02 12 break-when-value-changes-data-breakpoints-for-net-core-in-visual-studio-2019      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

[visual-studio] Break when a value changes using the Visual Studio debugger

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