On Friday, 6 December 2019 09:48:51 CET Giuseppe D'Angelo via Interest wrote: > Il 06/12/19 09:42, Uwe Rathmann ha scritto: > > Something you can try is to include the moc file at the end of your cpp > > file. This can be done like this: > > > > #include "moc_XYZ.cpp" > > > > This type of construction is at least supported by qmake. > > > > This does not reduce the number of moc runs, but it reduces the number > > of compiler runs. As a rule of thumb for not too large classes I would > > expect, that ~50% of the compile time is spent inside the Qt headers and > > by including the moc file the overall compile time goes down by 33% as > > the headers need to be processed only once. > > This trick is used in several places in Qt itself (look for "includemoc" > in commits). Not only it helps build times but also it produces slightly > better code overall.
Heya, On that note, CMake goes one step further and removes the need to do this manually. Using CMake's AUTOMOC feature, CMake will automatically create ONE mocs_compilations.cpp file per target which in turn includes all generated "moc_XYZ.cpp" files. Quoting: "Header files that are not included by an #include "moc_<basename>.cpp" statement are nonetheless scanned for Q_OBJECT or Q_GADGET macros. The resulting moc_<basename>.cpp files are generated in custom directories and automatically included in a generated <AUTOGEN_BUILD_DIR>/mocs_compilation.cpp file, which is compiled as part of the target." ... from: https://cmake.org/cmake/help/v3.9/prop_tgt/AUTOMOC.html Just as a side note. So if you thought about moving to CMake anyway this might be a good reason for a start. In general switching to e.g. CMake with the Ninja generator will give you better overall build times, esp. on Windows. And you said: > We probably don't strictly need the Q_OBJECT macro in some of those > classes, but I would prefer not to start removing Q_OBJECT unless that's > the last option. I'd rethink that opinion: Adding the Q_OBJECT (and thus inheriting from QObject) everywhere adds the dependency to moc (=> slower compilation time) and has a runtime performance impact (QObject creation is not cheap!). I'd consider only requiring Q_OBJECT where needed, it leads to overall better code. Regards, Kevin > HTH, -- Kevin Funk | kevin.f...@kdab.com | Senior Software Engineer KDAB (Deutschland) GmbH, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt, C++ and OpenGL Experts
smime.p7s
Description: S/MIME cryptographic signature
_______________________________________________ Interest mailing list Interest@qt-project.org https://lists.qt-project.org/listinfo/interest
