Just-In-Time Debugging

Article
09/11/2012

Just-In-Time debugging launches Visual Studio automatically when an exception or crash occurs in an application running outside Visual Studio. This enables you to test your application when Visual Studio is not running and begin debugging with Visual Studio when a problem occurs.

Just-In-Time debugging does not work for Windows Store apps. Just-In-Time debugging does not work for managed code that is hosted in a native application, such as Visualizers.

Using Just-In-Time debugging

When you install Visual Studio, Just-In-Time debugging is enabled by default. If you need to disable or reenable Just-In-Time debugging, see Enabling or disabling Just-In-Time Debugging.

When Just-In-Time debugging is enabled, you can test your application outside of Visual Studio. When a crash or exception occurs, you will see a dialog box appears with a message that looks something like this:

An unhandled exception ('System.TypeInitializationException') occurred in terrarium.exe[3384]

When this dialog box appears, you can begin debugging with the following procedure.

To begin Just-In-Time debugging when an error occurs

In the Just-In-Time Debugging dialog box, in the Possible Debuggers list, click New instance of Visual Studio 2012 or click an instance of Visual Studio that is already running.
To use Visual Studio automatically for all future crashes, click Set the currently selected debugger as the default.
If you want to choose what types of code you will be able to debug, click Manually choose the debugging engines. If you do not choose this option, Visual Studio automatically selects the appropriate debug engines for the type of code in your program.
Click OK.
If your application contains an assembly with untrusted code, a dialog box with a security warning appears. This dialog box enables you to decide whether or not to proceed with debugging. Before you continue with debugging, decide whether you trust the code. Did you write the code yourself? Do you trust the coder? If the application is running on a remote machine, do you recognize the name of the process? Even if the application is running locally, that does not necessarily mean it can be trusted. In Internet Explorer, for example, a malicious ActiveX control could be running. Consider the possibility of such malicious code running on your computer. If you decide that the code you are about to debug is trustworthy, click Debug. Otherwise, click Don't Debug.

Enabling or disabling Just-In-Time debugging

You can enable or disable Just-In-Time debugging from the Options dialog box.

To enable or disable Just-In-Time debugging

On the Tools menu, click Options.
In the Options dialog box, select the Debugging folder.
In the Debugging folder, select the Just-In-Time page.
In the Enable Just-In-Time debugging of these types of code box, select or clear the relevant program types: Managed, Native, or Script.

To disable Just-In-Time debugging, once it has been enabled, you must be running with Administrator privileges. Enabling Just-In-Time debugging sets a registry key, and Administrator privileges are required to change that key.
Click OK.

By default, Windows Forms applications have a top-level exception handler that allows the program to continue to run if it can recover. As a result, you must perform the following additional steps to enable Just-In-Time debugging of a Windows Forms application.

To enable Just-In-Time debugging of a Windows Form

Set the jitDebugging value to true in the in the system.windows.form section of the machine.config or application.exe.config file:
```
<configuration>
    <system.windows.forms jitDebugging="true" />
</configuration>
```
In a C++ Windows Form application, you must also set DebuggableAttribute in a .config file or in your code. If you compile with /Zi and without /Og, the compiler sets this attribute for you. If you want to debug a non-optimized release build, however, you must set this yourself. You can do this by adding the following line to your the AssemblyInfo.cpp file of your application:
```
[assembly:System::Diagnostics::DebuggableAttribute(true, true)]; 
```
For more information, see DebuggableAttribute.

Just-In-Time debugging may still be enabled even if Visual Studio is no longer installed on your computer. When Visual Studio is not installed, you cannot disable Just-In-Time debugging from the Visual Studio Options dialog box. In that case, you can disable Just-In-Time debugging by editing the Windows registry.

To disable Just-In-Time debugging by editing the registry

On the Start menu, search for and run regedit.exe
In the Registry Editor window, locate and delete the follow registry keys:
- HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug\Debugger
- HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\DbgManagedDebugger
If your computer is running a 64-bit operating system, delete the following registry keys also:
- HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\AeDebug\Debugger
- HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\DbgManagedDebugger
Take care not to accidentally delete or change any other registry keys.
Close the Registy Editor window.