_DEBUG vs. NDEBUG: When Should You Use Which Debug Preprocessor Definition?

_DEBUG vs NDEBUG: Understanding Debug Preprocessor Definitions

In C programming, preprocessor defines are used to conditionally include or exclude code based on certain conditions. When it comes to debugging sections of code, two common preprocessor defines are _DEBUG and NDEBUG.

_DEBUG:

_DEBUG is a preprocessor define specific to Microsoft Visual Studio. It is set when using the /MTd or /MDd compilation options. When _DEBUG is defined, it enables debugging-specific features, such as additional runtime assertions and memory debugging capabilities.

NDEBUG:

NDEBUG is a standard C preprocessor define that disables standard-C assertions. Assertions are used to test for errors during runtime. When NDEBUG is defined, it suppresses these assertions, potentially improving performance.

Usage Recommendations:

• Use _DEBUG when you require debugging code consistent with MS CRT debugging techniques, particularly when working with Visual Studio.
• Use NDEBUG when you want to adhere to standard assert() behavior, even with MS CRT.

Custom Debugging Macros:

If you prefer defining your own custom debugging macros, avoid using names beginning with an underscore, as these are typically reserved by the compiler or runtime.

Example Usage:

#ifdef _DEBUG
    // Debugging code, specific to MS CRT
#else
    // Release code, without assertions
#endif

Remember to use these preprocessor defines judiciously, as excessive conditional compilation can impact code readability and maintainability.

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