[Development] Using #pragma once
thiago.macieira at intel.com
Sun Oct 7 20:39:22 CEST 2018
On Sunday, 7 October 2018 01:56:47 PDT Lars Knoll wrote:
> Just a quick question: Does anybody have any good arguments against us
> starting to use #pragma once instead of header guards throughout our code
a) not supported everywhere
b) not well-defined behaviour when it comes to anything but the simplest
For example, I have ~/src as a bind-mount to ~/dev/src. That means
are actually the same file, but they aren't for the effects of #pragma once
because the paths differ.
Another problem is qcompilerdetection.h, qprocessordetection.h,
qsystemdetection.h, qtypeinfo.h, etc. which depend on the header guards to
break the include cycle. Ditto for qlist.h + qstringlist.h and
> I’ve started using it implicitly when updating 3rd party code (the macro
> assembler) in qtdeclarative without any problems (so I’d supported by all
> our compilers). IMO #pragma once is both safer and nicer to use than
> classic header guards.
On all the compilers that compile that macro assembler. We still have
architectures where they don't.
Another aspect is that the macro assembler headers don't get installed and
aren't subject to syncqt.pl, so their hierarchy is a lot simpler than for Qt's
I recommend against changing Qt.
Thiago Macieira - thiago.macieira (AT) intel.com
Software Architect - Intel Open Source Technology Center
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