how to use if else macro while compilation

[devphylosoff]

I have cpp file with :

#if 1
#include"myfile.h"
#else
#include "libfile.h"
#endif

how it works ?

[Victor Bazarov]

devphylosoff wrote:

I have cpp file with :

#if 1
#include"myfile.h"
#else
#include "libfile.h"
#endif

how it works ?

The preprocessor lets through everything between '#if 1' and '#else'
and drops everything between '#else' and '#endif'. The result of
the filtering is

#include"myfile.h"

which then preprocessed, and then the code from 'myfile.h' is itself
included and preprocessed.

V
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[Neelesh Bodas]

On Sep 19, 9:44 pm, devphylosoff <[e-mail]:

I have cpp file with :

#if 1
#include"myfile.h"
#else
#include "libfile.h"
#endif

how it works ?

w.r.t. subject line: "macros" are considered in the pre-processing
stage, which comes before compilation.

The preprocessor evaluates the #if macro and expands the appropriate
clause(s).
In the above example, since 1 evaluates to true, the file "myfile.h"
will get included.

-N

[devphylosoff]

rights, #if 1 is always true, so if I need switch I should use
different condition.

for example
#if sth
....

and compile with -Dsth.
it's really no way to make #if 1 equals false using -D ?

[Michal Nazarewicz]

devphylosoff <de*****@gmail.comwrites:

I have cpp file with :

#if 1
#include"myfile.h"
#else
#include "libfile.h"
#endif

how it works ?

Any textbook on C or C++ should explain that. If condition given in #if
statement is true the portion between #if and #else will be compiled
otherwise the part between #else and #endif. (There is also #ifdef,
#ifndef, #elsif.)

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[Chris Thomasson]

"Michal Nazarewicz" <mi****@tlen.plwrote in message
news:87************@erwin.mina86.com...
[...]

Any textbook on C or C++ should explain that. If condition given in #if
statement is true the portion between #if and #else will be compiled
otherwise the part between #else and #endif. (There is also #ifdef,
#ifndef, #elsif.)

[...]

#elif

[Michal Nazarewicz]

"Michal Nazarewicz" <mi****@tlen.plwrote:

>Any textbook on C or C++ should explain that. If condition given in #if
statement is true the portion between #if and #else will be compiled
otherwise the part between #else and #endif. (There is also #ifdef,
#ifndef, #elsif.)

"Chris Thomasson" <cr*****@comcast.netwrites:

#elif

Bah... Too much Perl. :P

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Best regards, _ _
.o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michal "mina86" Nazarewicz (o o)
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