Unhandled Exceptions

In Windows programming, an unhandled exception terminates the process unless a debugger is attached or a structured exception handler (SEH) is present. This article explains how to detect, diagnose, and mitigate unhandled exceptions in native and managed code.

Overview
Native (C/C++) Exceptions
Managed (.NET) Exceptions
Debugging Unhandled Exceptions
Best Practices

Overview

When an exception propagates out of the top‑level thread entry point without being caught, Windows raises a EXCEPTION_UNHANDLED event. The default behaviour is to display the Windows Error Reporting (WER) dialog and terminate the process.

Native (C/C++) Exceptions

Windows uses Structured Exception Handling (SEH) to manage low‑level exceptions such as access violations.

#include <windows.h>
#include <stdio.h>

int main()
{
    __try
    {
        int *p = NULL;
        *p = 42; // Access violation
    }
    __except(EXCEPTION_EXECUTE_HANDLER)
    {
        printf("Caught an access violation!\\n");
    }
    return 0;
}

For C++ exceptions, use try/catch blocks or combine with SEH via __try/__except.

Managed (.NET) Exceptions

In .NET, unhandled exceptions on any thread cause the runtime to invoke AppDomain.UnhandledException. You can subscribe to this event to log or perform cleanup.

using System;

class Program
{
    static void Main()
    {
        AppDomain.CurrentDomain.UnhandledException += (s, e) =>
        {
            Console.WriteLine("Unhandled exception: " + ((Exception)e.ExceptionObject).Message);
        };

        throw new InvalidOperationException("Oops!");
    }
}

Debugging Unhandled Exceptions

Use Visual Studio or WinDbg to capture a crash dump. Enable WER local dump collection:

reg add "HKLM\SOFTWARE\Microsoft\Windows\Windows Error Reporting\LocalDumps" /v DumpFolder /t REG_EXPAND_SZ /d "%LOCALAPPDATA%\\CrashDumps" /f
reg add "HKLM\SOFTWARE\Microsoft\Windows\Windows Error Reporting\LocalDumps" /v DumpType /t REG_DWORD /d 2 /f

After a crash, open the .dmp file in WinDbg and run !analyze -v to view the exception stack.

Best Practices