C/C++ preprocessor directive check defined and string not empty [duplicate]

Question

I'm trying to obtain something like:

#if (!defined(SVN_REV) || (SVN_REV==""))
   char svnrev[10]="not found";
#else
   char svnrev[16]=SVN_REV;
#endif

to handle the case that the compiler, not finding a particular environment variable, sets:

define SVN_REV ""

which for me should be treated same as the define is missing.

But it seems that this is not possible, did anybody found a way to achieve the result?

Visual C++ is complaining that it is "invalid integer constant expression", didn't try on linux gcc/g++ yet — giuspen
– giuspen, Commented Jan 23, 2015 at 15:28
Why not char svnrev[]="not found"; Let it count the characters for you. — Neil Kirk
– Neil Kirk, Commented Jan 23, 2015 at 16:10
What is "C/C++"? Why is this question tagged C if you are actually writing C++? — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Jan 23, 2015 at 16:20

unwind · Accepted Answer · 2015-01-23 15:29:18Z

0

No, the C preprocessor doesn't compare strings.

You can do:

#if !defined SVN_REV
#define SVN_REV "not found"
#endif
const char *svnrev = SVN_REV;

To achieve the same effect.

answered Jan 23, 2015 at 15:29

unwind

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2 Comments

giuspen Over a year ago

But this does not cover the case that Visual C++ (which in the case does not find a particular environment variable) defines SVN_REV as an empty string - so it is defined but as empty which for me is like not defined. Probably it is not possible to obtain the result only with preprocessor code.

Zordid Over a year ago

This is not an answer to the question... :(

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