_DEBUG vs. NDEBUG: Which Preprocessor Macro Should You Use for Debugging?

Understanding the Preprocessor Macros _DEBUG and NDEBUG

When specifying sections of code specifically intended for debugging, programmers often grapple with the question of which preprocessor define to utilize. This article aims to shed light on the options available, discussing the usage and implications of _DEBUG, NDEBUG, and custom macros.

_DEBUG vs. NDEBUG

Both _DEBUG and NDEBUG are widely used preprocessor macros. _DEBUG is commonly associated with Microsoft's Visual Studio development environment, while NDEBUG is a standard macro defined by the C/C standard library.

_DEBUG is typically set when the "/MTd" or "/MDd" compiler options are specified. These options enable runtime library routines specifically tailored for debugging purposes.

On the other hand, NDEBUG is commonly used to disable standard C assertions (assert()), which are useful for debugging but may slow down performance in non-debug scenarios.

When to Use Which?

The choice between _DEBUG and NDEBUG depends on the specific requirements of the code and the development environment being used. If the primary concern is to align with Microsoft CRT debugging practices, _DEBUG offers a convenient solution.

If the goal is to ensure compatibility with standard assert() behavior, NDEBUG is a suitable option. However, it is important to note that NDEBUG may not disable all debugging functionality in some compilers.

Custom Macros

Programmers may also consider defining their own custom debugging macros, but it is generally advised to avoid starting macro names with an underscore. Reserved by convention, using an underscore may interfere with compiler or C runtime behavior.

Conclusion

To specify debug sections of code, _DEBUG and NDEBUG serve as established preprocessor macros. _DEBUG, aligned with Visual Studio C Runtime, offers specific debugging techniques, while NDEBUG favors standard C assertions and compatibility. Custom debugging macros provide flexibility but should be used judiciously. Understanding these options enables programmers to effectively manage debugging code in their projects.

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