---
description: "Learn more about: _DEBUG"
title: "_DEBUG"
ms.date: "11/04/2016"
helpviewer_keywords: ["DEBUG macro", "_DEBUG macro"]
ms.assetid: a9901568-4846-4731-a404-399d947e2e7a
---
# `_DEBUG`

The compiler defines `_DEBUG` when you specify the /MTd or /MDd option. These options specify debug versions of the C run-time library.

For more information, see [CRT debugging techniques](./crt-debugging-techniques.md).

## See also

[Control flags](./control-flags.md)