DEBUG vs NDEBUG

Question

Which preprocessor define should be used to specify debug sections of code   Use  ifdef  DEBUG or  ifndef NDEBUG or is there a better way to do it  e g   define MY DEBUG   I think  DEBUG is Visual Studio specific  is NDEBUG standard

User · Accepted Answer

Visual Studio defines  DEBUG when you specify the  MTd or  MDd option  NDEBUG disables standard-C assertions  Use them when appropriate  ie  DEBUG if you want your debugging code to be consistent with the MS CRT debugging techniques and NDEBUG if you want to be consistent with assert     If you define your own debugging macros  and you don t hack the compiler or C runtime   avoid starting names with an underscore  as these are reserved

User · Answer

Be consistent and it doesn t matter which one  Also if for some reason you must interop with another program or tool using a certain DEBUG identifier it s easy to do   ifdef THEIRDEBUG  define MYDEBUG  endif   and vice-versa

User · Answer

Unfortunately DEBUG is overloaded heavily  For instance  it s recommended to always generate and save a pdb file for RELEASE builds  Which means one of the -Zx flags  and -DEBUG linker option  While  DEBUG relates to special debug versions of runtime library such as calls to malloc and free  Then NDEBUG will disable assertions

User · Answer

The macro NDEBUG controls whether assert   statements are active or not  In my view  that is separate from any other debugging - so I use something other than NDEBUG to control debugging information in the program  What I use varies  depending on the framework I m working with  different systems have different enabling macros  and I use whatever is appropriate  If there is no framework  I d use a name without a leading underscore  those tend to be reserved to  the implementation  and I try to avoid problems with name collisions - doubly so when the name is a macro

User · Answer

I rely on NDEBUG  because it s the only one whose behavior is standardized across compilers and implementations  see documentation for the standard assert macro    The negative logic is a small readability speedbump  but it s a common idiom you can quickly adapt to   To rely on something like  DEBUG would be to rely on an implementation detail of a particular compiler and library implementation   Other compilers may or may not choose the same convention   The third option is to define your own macro for your project  which is quite reasonable   Having your own macro gives you portability across implementations and it allows you to enable or disable your debugging code independently of the assertions   Though  in general  I advise against having different classes of debugging information that are enabled at compile time  as it causes an increase in the number of configurations you have to build  and test  for arguably small benefit   With any of these options  if you use third party code as part of your project  you ll have to be aware of which convention it uses

User · Answer

Is NDEBUG standard    Yes it is a standard macro with the semantic  Not Debug  for C89  C99  C  98  C  2003  C  2011  C  2014 standards  There are no  DEBUG macros in the standards   C  2003 standard send the reader at  page 326  at  17 4 2 1 Headers  to standard C       That NDEBUG is similar as This is the same as the Standard C library    In C89  C programmers called this standard as standard C  in  4 2 DIAGNOSTICS  section it was said     http   port70 net  nsz c c89 c89-draft html      If NDEBUG is defined as a macro name at the point in the source file   where  is included  the assert macro is defined simply as        define assert ignore    void 0     If look at the meaning of  DEBUG macros in Visual Studio https   msdn microsoft com en-us library b0084kay aspx  then it will be seen  that this macro is automatically defined by your  hoice of language runtime library version

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