C# compilation time for large projects (compared to C++)

Question

I often hear people praise the compilation speed of C#. So far I have only made a few tiny applications, and indeed I noticed that compilation was very fast. However, I was wond

Answer 1

C++ is so slow to compile as the header files have to be reread and reparse every time they are included. Due to the way “#defines” work, it is very hard for a compiler to automatically pre-compile all header files. (Modula-2 made a much better job of this) Having 100s of headers read for each C++ file that is compiled is normal on a lot of C++ projects.

Sometimes incremental c++ compiles can be a lot faster than C#. If you have all your C++ header files (and design) in a very good state (see books like Large-Scale C++ Software Design, Effective C++) You can make a change to the implementation of a class that is used by most of the system and only have one dll recompile.

As C# does not have separate header files whenever you change the implantation of a class, all uses of the class get recompiled even if the public interface of the class has not changed. This can be reduced in C# by using “interface based programming” and “dependency injection” etc. But it is still a pain.

However on the whole I find that C# compiles fast enough, but large C++ projects are so slow to compile that I find myself not wanting to add a methods to a “base class” due to the time of the rebuild.

Having lots of Visual Studio projects with a handful of classes in each can slow down C# builds a lot. Combining related projects together and then “trusting” the developers not to use class that are private to a namespace can at times have a great benefit. (nDepends can be used to check for people breaking the rules)

(When trying to speed up C++ compiles I have found FileMon very useful. One project I worked on, the STL was added to a header file and the build got a lot slower. Just adding STL to the precompiled header file made a big difference! Therefore track your build time and investigate when it gets slower)