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Macro expansion in VC++

, 4 Feb 2012
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Expanding a macro in VC++
Let us assume for some unknown reason, we have to write a macro [yes, yes, I know Macros are evil and can be substituted by in-line and template function friendlies - but just in case] or say if we are trying to understand an existing macro in some legacy code.
In these situations, it would be nice if we can see how exactly this macro is expanded by the compiler. This tip suggests a way to do so.
Look at this:

#define SQUARE(A) (A * A) 
void main(int argc, char* argv[])
    int y = 2;
    int s = SQUARE(++y); // Due to this the macro expands in a 
                         // different way and we will get abnormal results
                         // To debug, we have to see how this macro is expanded
                         // by the compiler 
We all know that the value of s will be 16 (rather than 4). To see how the macro expands,
Go to VS command prompt and enter:
cl /EP C:\Test\main.cpp > C:\Test\macro.txt
This command will expand the macro and dump it in macro.txt. The dump looks like
void main(int argc, char* argv[])
    int y = 2;
    int s = (++y * ++y);
See our macro is expanded.
And DO NOT down vote me:
  1. If you do not like macros (I too hate them, but ....)
  2. If this is old trick / re-post (I just want to share)
Yes, there could be many alternatives and this is one.
Thanks (:-


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Lakamraju Raghuram
Software Developer
India India
Did my masters from IIT-M in Advanced Manufacturing Technology and I am working mainly on C++ from 2004 onwards.

Comments and Discussions

GeneralMy vote of 3 Pinmemberrahman_tanzilur0113-Jan-13 11:00 
QuestionVS addin Pinmembersokolov765-Aug-12 23:04 
AnswerRe: VS addin PinmemberLakamraju Raghuram6-Aug-12 1:51 
GeneralMy vote of 5 PinmemberVolynsky Alex19-May-12 1:33 
GeneralRe: This way of analysis is cool .... how many will scroll thoug... PinmemberLakamraju Raghuram31-Jan-12 7:03 
GeneralRe: Technically you should wrap the usage of macro arguments wit... PinmemberChuck O'Toole4-Feb-12 16:22 
GeneralReason for my vote of 5 Good tip PinmemberManish K. Agarwal20-Feb-12 0:12 
GeneralReason for my vote of 5 Very well explained PinmemberJoxemi7-Feb-12 4:42 
GeneralReason for my vote of 5 Helped resolve 3rd party library API... Pinmembermriddle6-Feb-12 13:06 
GeneralIt would add to the article to describe why the result is 16... Pinmembernv33-Feb-12 2:41 

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