Safer conditional compilation?

In an MSVC C++ program I have a part of code which I want to enable or disable depending on a preprocessor definition

// 1.h
#ifdef MYOPTION
//...
#endif

But I find that it is quite dangerous when it is used in a .h file included in more than one compilation unit, as I can easily get inconsistent headers (I don't want to define MYOPTION globally as it would require a complete recompilation each time I change it):

// 1.cpp
#define MYOPTION
#include "1.h"

// 2.cpp
#include "1.h"

Of course, it is much more complicated than this simplified example due to the chained header inclusion.

Is there a way to avoid such inconsistency, e.g. have a compile-time error without too much effort?

I thought of doing #define MYOPTION 0 or 1, but then I would have to write something like

#if MYOPTION == 1
//...
#elif !defined(MYOPTIO开发者_JS百科N)
#error ...
#endif

which looks too complicated... Maybe there is a better option?

How about something like this: have 1.h define a dummy section in the obj with different options. This way, if MYOPTION is ever used inconsistently, the linker will issue a warning.

1.h:

#ifdef MYOPTION
#pragma section("MYOPTION_GUARD",write)
#else
#pragma section("MYOPTION_GUARD",read)
#endif

namespace { __declspec(allocate("MYOPTION_GUARD")) int MYOPTION_guard; }

Compiling with MYOPTION defined in a.cpp but not in b.cpp yields this linker warning (using VC 2008):

b.obj : warning LNK4078: multiple 'MYOPTION_GUARD' sections found with different attributes (40300040)

A consistent definition yields no linker warnings at all.

I think you've listed most solution yourself, basically. I would use the last solution, but perhaps in a slightly different form:

#ifndef MYOPTION
#error ...
#endif

...

#if MYOPTION == 1
//...
#endif

Because often this #if MYOPTION == 1 will appear more than once in each file. It's also clearer that MYOPTION is a requisite for that file.

You say it "looks too complicated", but I'm afraid there's probably no solution that's less "complicated" than this.

Assuming that you actually need to use the defines, better is to define them via the compiler command line than #define in your source files. Then your configure script/makefile/build process sets the define once and you're guaranteed that it will agree properly across all source files.

Perhaps what you want is to create a separate configuration.

You can go to Build -> Configuration Manager and create a new configuration (separate from DEBUG, RELEASE). Creating a new configuration will allow you to define preprocessor symbols specific to that configuration.

For example, with a new configuration titled "MyOption 1" you could add the preprocessor definition MYOPTION = 1. The same thing goes with MYOPTION = 2, 3, ...

Each configuration has to be built separately. DEBUG and RELEASE are examples of separate configurations; DEBUG defines _DEBUG and RELEASE defines NDEBUG