Re: #defining a comment

From:

"Axter" <google@axter.com>

Newsgroups:

comp.lang.c++

Date:

5 Jun 2006 11:39:36 -0700

Message-ID:

<1149532776.184892.11730@f6g2000cwb.googlegroups.com>

hobbes_7_8@yahoo.com wrote:

Hi everybody!

This is basically a pre-processor doubt. I have this very simple
define:

#ifdef NDEBUG
#define QTRACE //
#else
#define QTRACE qDebug()
#endif

... so that the line:

QTRACE << "Foi lido o valor" << *it;

... is expanded to:

qDebug() << "Foi lido o valor" << *it;

... in debug mode, and is expanded to:

// << "Foi lido o valor" << *it;

... in release mode. Unfortunately compilation yields:

main.cpp(17) : error C2143: syntax error : missing ';' before '<<'

... Meaning the pre-processor expanded the macro to absolutely nothing
:( Does anyone know a way to overcome this? I'm developing this on
Visual Studio .NET 2003 but it will run on a HP-UX system, so I can't
rely on any Microsoft extension.

Thanks in advance,

Andr=E9

I recomend you use the following method:
#ifdef NDEBUG
#define QTRACE if (1);else qDebug()
#else
#define QTRACE qDebug()
#endif

Most compilers will optimize away the No-Debug QTRACE.

When using this method, it's important to use if(1);else instead of if
(0)
The reason you want to do this is to avoid incorrect logic flow with
code like the following:

if (foofoo == 0 )
QTRACE("Error: No foofoo");
else
printf("We have some foofoo.");

By using an if(1);else in the macro, the above printf will still get
called if foofoo is not zero.