stdafx.h cross platform without issues?

Question

Hey i've been following learncpp.com tuts for the last couple days, they say to comment out "#include "stdafx.h" from .cpp files for Code::Blocks.

Is that a must, to remove the include line? What happens if you had hundreds of files and changed from Visual Studio on Win7 to Code::Blocks on Linux or hand it off to someone else with a mac?

Transfix

What happens if you don't comment it out? Did you try? – Robbegrillet

Answer 1

stdafx.h is the idiomatic name used for precompiled headers in the Visual Studio ecosystem. In a nutshell, it's a regular header, but the contents of this file will be compiled once and reused for all cpp files in the project.

That is useful since in most projects, a large number of headers (standard library, system header, shared project-wide definitions) are used by virtually all translation units (cpps), so using PCH is a huge performance benefit during compilation

(Actually, PCH is a hack to workaround C++' inefficient compilation and linkage model and it's a shame that we need to maintain it by hand … oups, blasphemy.)

But this also means that - as long as the contents of your stdafx.h are gcc-compatible - compilation with CodeBlocks should still work, but without the immediate performance benefit.

The stdafx.h generated by VS' app wizards doesn't work out of the box on other platforms - it typically includes Windows.h. So to make it work, guard the Windows-specific definitions with appropriate #ifdef/#endif pairs and vice versa for Linux or Mac-specific stuff.

Britanybritches

My VS2010 did not include one called windows.h, it added targetver.h stdio.h tchar.h, thats it. Otherwise i should be fine sending whatever i make to my friend on ubuntu? – Transfix

Just try it - it's essentially just a header file with a special name as mentioned above. You're more likely to hit other compatibility issues e.g. when working with format strings or different string functions. – Larry

Answer 2

No, that tutorial advice does not make any sense. stdafx.h does not break anything at all. The system of pre-compiled headers in Visual Studio compiler is intentionally designed that way.

If your compiler supports pre-compiled headers (and follows the same pre-compilation approach as Visual Studio), it can use stdafx.h for pre-compiling.

If your compiler does not support pre-compiled headers (or used a different pre-compilation approach), then stdafx.h is interpreted as an ordinary header file, no different from any other header file and processed the same way as any other header file.

It is possible that what is meant by that tutorial is that stdafx.h often includes some Windows-specific headers, not present on other platform. While it is possible, it really has nothing to do with stdafx.h itself at all. Obviously, if you are compiling your program on some other platform you should not attempt to include any Windows headers, regardless of how you are doing it: through stdafx.h or somewhere else.

Exurb

Answer 3

As far as I'm aware stdafx.h is a Windows-only file (for precompiled headers): Your code will just fail to compile if you don't comment it out.

Gaitskell

Answer 4

If you are not actually using a precompiled header (PCH), I advise going into Visual Studio's Options/Preferences->Precompiled Header and turning them off. If you try to remove them and still use Visual Studio, you will get a ton of errors.

Keffiyeh

Answer 5

The only thing to actually do is to include the path containing the stdafx.h (or precompiled header) in the default include path list. This is needed because the MS compiler actually replaces the #include "stdafx.h" with the precompiled data without really looking for the header.

Other compilers will usually want to pull in the data. But it should rather not be commented out. Usually you'll be able to tune your compiler to also make use of the precompiled header features to boost up compilation. With gcc that would be done with the -pch option. With Code Blocks I could find this wiki. Precompiled headers are not evil, on the contrary they will save you precious time if understood and used adequately.

Ballew