tui-cs/Terminal.Gui · warning · ApplicationException

Failed to set output console mode, error code: {GetLastError

Error message

Failed to set output console mode, error code: {GetLastError()}.

What it means

This error is thrown by WindowsVTOutputHelper.TryEnable() when SetConsoleMode fails while adding ENABLE_VIRTUAL_TERMINAL_PROCESSING to the output handle. Unlike NetWinVTConsole, TryEnable is designed to be fault-tolerant -- the thrown ApplicationException is immediately caught by the surrounding try/catch (WindowsVTOutputHelper.cs:127) and converted to a logged warning returning false. The user normally sees only a warning, not the exception, unless examining logs.

Source

Thrown at Terminal.Gui/Drivers/WindowsHelpers/WindowsVTOutputHelper.cs:107

                return false;
            }

            if (!GetConsoleMode (OutputHandle, out _originalConsoleMode))
            {
                Logging.Warning ("Failed to get Windows console mode.");

                return false;
            }

            uint newMode = _originalConsoleMode;

            if ((newMode & ENABLE_VIRTUAL_TERMINAL_PROCESSING) == 0)
            {
                newMode |= ENABLE_VIRTUAL_TERMINAL_PROCESSING;

                if (!SetConsoleMode (OutputHandle, newMode))
                {
                    throw new ApplicationException ($"Failed to set output console mode, error code: {GetLastError ()}.");
                }
            }

            if ((newMode & ENABLE_PROCESSED_OUTPUT) == 0)
            {
                newMode |= ENABLE_PROCESSED_OUTPUT;

                if (!SetConsoleMode (OutputHandle, newMode))
                {
                    throw new ApplicationException ($"Failed to set output console mode, error code: {GetLastError ()}.");
                }
            }

            IsEnabled = true;

            //Logging.Information ($"Windows VTS output mode enabled successfully. Mode: 0x{newMode:X} (was 0x{_originalConsoleMode:X})");

            return true;

View on GitHub (pinned to 2e47b11478)

Solutions

Check the application log for the warning 'Failed to enable Windows VTS mode' -- the underlying Win32 error code is in the exception message.
Upgrade the Windows version or console host to one supporting VT processing.
If VT is unavailable, select the legacy WindowsDriver via Application.ForceDriver = "Windows".
Since TryEnable already catches and logs this, usually no action is needed unless VT rendering was expected -- investigate the Win32 error code.

Example fix

// before -- relying on VT, which silently fails on old consoles
using IApplication app = Application.Create().Init();

// after -- check logs; force legacy driver if VT is unsupported
Application.ForceDriver = "Windows";
using IApplication app = Application.Create().Init();

Defensive patterns

Strategy: fallback

Try / catch

// TryEnable already catches this internally and returns false;
// check the return value or logs
if (!windowsVTOutputHelper.TryEnable())
{ Logging.Warning("VT output could not be enabled; falling back to legacy rendering."); }

Prevention

Monitor application logs for 'Failed to enable Windows VTS mode' warnings.
Upgrade Windows to a version supporting VT processing.
Force the legacy WindowsDriver if VT is unavailable.
Note that TryEnable already handles this gracefully -- usually no action needed.

When it happens

Trigger: Thrown at WindowsVTOutputHelper.cs:107 when (newMode & ENABLE_VIRTUAL_TERMINAL_PROCESSING) == 0 and SetConsoleMode(OutputHandle, newMode | ENABLE_VIRTUAL_TERMINAL_PROCESSING) returns false. The OutputHandle is obtained from TerminalDevice.OutputHandle (CONOUT$). Because TryEnable wraps this in try/catch, the exception is caught and TryEnable returns false.

Common situations: Running on a Windows version or console host without VT processing support, the output handle being invalid despite being non-zero, or the console being in a restricted mode. The user-facing symptom is a logged warning 'Failed to enable Windows VTS mode' and VT rendering being disabled (falling back to legacy rendering).

Related errors

AI-assisted analysis of tui-cs/Terminal.Gui@2e47b11478 (2026-08-13). Data as JSON: /api/errors/2f7154148a2523d8. Report an issue: GitHub.