Break when a value changes using the Visual Studio debugger

Question

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.

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; }

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: &(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: &(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.

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;
    }
}