Inspect variables and return values in the Visual Studio debugger

When you try to debug an issue, you're often attempting to find out whether variables are storing the values that you expect them to have in a particular app state. Some of the most useful features of the debugger are those that allow you to inspect variables.

This article shows you how to inspect variables and view return values using the debugger in Visual Studio. The debugger provides several convenient ways to perform these tasks, including the following:

• In the code editor, you can view data tips and inline return values
• In debugger windows (Autos, Locals, and Watch windows), you can view variable values
• In visualizers, you can view large strings or complex .NET objects

These features are only available while debugging. To learn how to start a debugging session, see Start debugging and enter break mode.

View variables in the code editor

Often, when debugging, you want a quick way to check property values on objects in the code editor, and the data tips are a good way to do it.

While paused in the debugger, hover over an object with the mouse and you see its value, or its default property value.

If the variable has properties, you can expand the object to see all its properties.

For detailed information on using data tips, see View data values in data tips.

Set a watch on variables

You can use a Watch window to specify a variable (or an expression) that you want to keep an eye on.

While debugging, right-click an object in the code editor and choose Add Watch. A Watch window opens.

In this example, you've a watch set on the object, and you can see its value change as you move through the debugger. Unlike the other variable windows, the Watch windows always show the variables that you're watching (they're grayed out when out of scope).

For detailed information, see Set a Watch using the Watch and QuickWatch Windows.

Inspect variables in debugger windows (Autos and Locals)

The Autos and Locals windows show variable values while you're debugging. The windows are only available during a debugging session. The Autos window shows variables used around the current statement where the debugger is paused. The Locals window shows variables defined in the local scope, which is usually the current function or method.

• To open the Autos window, while debugging, select Debug > Windows > Autos, or press Ctrl+Alt+V > A.

  The Autos window is available for C#, Visual Basic, C++, and Python code, but not for JavaScript or F#.

• To open the Locals window, while debugging, select Debug > Windows > Locals, or press Alt+4.

Expandable arrays and objects show up in the Autos and Locals windows. Select the arrow to the left of a variable name to expand the view to show fields and properties. Here is an example of a System.IO.FileStream object in the Locals window:

A red value in the Locals or Autos window means the value has changed since the last evaluation. The change could be from a previous debugging session, or because you have changed the value in the window.

The default numeric format in debugger windows is decimal. To change it to hexadecimal, right-click in the Locals or Autos window and select Hexadecimal Display. This change affects all debugger windows.

Edit variable values in the Autos or Locals window

To edit the values of most variables in the Autos or Locals windows, double-click the value and enter the new value.

You can enter an expression for a value, for example a + b. The debugger accepts most valid language expressions.

In native C++ code, you might have to qualify the context of a variable name. For more information, see Context operator (C++).

Search in the Autos or Locals window

You can search for keywords in the Name, Value, and Type columns of the Autos or Locals window using the search bar above each window. Hit ENTER or select one of the arrows to execute a search. To cancel an ongoing search, select the "x" icon in the search bar.

Use the left and right arrows (Shift+F3 and F3, respectively) to navigate between found matches.

To make your search more or less thorough, use the Search Deeper dropdown list at the top of the Autos or Locals window to select how many levels deep you want to search into nested objects.

Pin properties in the Autos or Locals window

You can quickly inspect objects by their properties in the Autos and Locals windows with the Pinnable Properties tool. To use this tool, hover over a property and select the pin icon that appears or right-click and select the Pin Member as Favorite option in the resulting context menu. This bubbles up that property to the top of the object's property list, and the property name and value are displayed in the Value column. To unpin a property, select the pin icon again or select the Unpin Member as Favorite option in the context menu.

You can also toggle property names and filter out non-pinned properties when viewing the object's property list in the Autos or Locals windows. You can access each option by selecting the buttons in the toolbar above the Autos or Locals windows.

Change the context for the Autos or Locals window

You can use the Debug Location toolbar to select a desired function, thread, or process, which changes the context for the Autos and Locals windows.

To enable the Debug Location toolbar, click in an empty part of the toolbar area and select Debug Location from the dropdown list, or select View > Toolbars > Debug Location.

Set a breakpoint and start debugging. When the breakpoint is hit, execution pauses and you can see the location in the Debug Location toolbar.

Language differences in the Autos window (C#, C++, Visual Basic, Python)

Different code languages display different variables in the Autos window.

• In C# and Visual Basic, the Autos window displays any variable used on the current or preceding line. For example, in C# or Visual Basic code, declare the following four variables:

       public static void Main()
       {
          int a, b, c, d;
          a = 1;
          b = 2;
          c = 3;
          d = 4;
       }
  

  Set a breakpoint on the line c = 3;, and start the debugger. When execution pauses, the Autos window will display:

  

  

  The value of c is 0, because the line c = 3 has not yet been executed.

• In C++, the Autos window displays the variables used in at least three lines before the current line where execution is paused. For example, in C++ code, declare six variables:

       void main() {
           int a, b, c, d, e, f;
           a = 1;
           b = 2;
           c = 3;
           d = 4;
           e = 5;
           f = 6;
       }
  

  Set a breakpoint on the line e = 5; and run the debugger. When execution stops, the Autos window will display:

  

  

  The variable e is uninitialized, because the line e = 5 has not yet been executed.

View return values in the Autos window

In the following example, this C# code adds the return values of two functions:

static void Main(string[] args)
{
    int a, b, c, d;
    a = 1;
    b = 2;
    c = 3;
    d = 4;
    int x = sumVars(a, b) + subtractVars(c, d);
}

private static int sumVars(int i, int j)
{
    return i + j;
}

private static int subtractVars(int i, int j)
{
    return j - i;
}

To see the return values of the sumVars() and subtractVars() method calls in the Autos window:

1. Set a breakpoint on the int x = sumVars(a, b) + subtractVars(c, d); line.

2. Start debugging, and when execution pauses at the breakpoint, select Step Over or press F10. You should see the following return values in the Autos window:

   

   

Open a visualizer to inspect variables

While you're debugging in Visual Studio, you can view large strings or complex objects with built-in visualizers that make the data easier to inspect. For example:

• The string visualizer shows text, XML, HTML, and JSON strings that are too long for a data tip or debugger window. It can also help you identify malformed strings. For more information, see View strings in a string visualizer.
• The DataSet and IEnumerable visualizers show .NET collection objects in a tabular visualizer. For more information, see Tabular visualizers in Visual Studio) objects.

The visualizers appear in the Autos windows, data tips, and other debugger windows.

To open a visualizer, you must be paused during debugging. Hover over a variable that has a supported visualizer value, and select the magnifying glass icon .

Related content

• What is debugging?
• Debugging techniques and tools
• First look at debugging
• Debugger windows