When are C++ macros beneficial?


The C preprocessor is justifiably feared and shunned by the C++ community. In-lined functions, consts and templates are usually a safer and superior alternative to a #define.

The following macro:

#define SUCCEEDED(hr) ((HRESULT)(hr) >= 0)  

is in no way superior to the type safe:

inline bool succeeded(int hr) { return hr >= 0; }

But macros do have their place, please list the uses you find for macros that you can't do without the preprocessor.

Please put each use-cases in a seperate answer so it can be voted up and if you know of how to achieve one of the answers without the preprosessor point out how in that answer's comments.

6/3/2016 5:28:57 PM

Accepted Answer

As wrappers for debug functions, to automatically pass things like __FILE__, __LINE__, etc:

#ifdef ( DEBUG )
#define M_DebugLog( msg )  std::cout << __FILE__ << ":" << __LINE__ << ": " << msg
#define M_DebugLog( msg )
8/13/2009 8:10:03 PM

Methods must always be complete, compilable code; macros may be code fragments. Thus you can define a foreach macro:

#define foreach(list, index) for(index = 0; index < list.size(); index++)

And use it as thus:

foreach(cookies, i)
    printf("Cookie: %s", cookies[i]);

Since C++11, this is superseded by the range-based for loop.

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