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

Yes, C# normally compiles a lot faster. Not always fast enough though. My biggest C# codebase with maybe a million lines of code with lots of projects took about an hour to compile. But I suspect much of this time is due to visual studios poor build system. Compile time for C++ on the other hand is usually much longer, but is also much more dependent on how you organize your code. Poor handling of header file dependencies can easily increase compilation time with several orders of magnitude.

Answer 2

As far as I can tell from my own experience, yes, C# compiles a lot faster than C++ projects. Even for large applications.

This can be explained by the fact that C# is less complicated as a language than C++, and that C# is translated to IL (which can be optimized and translated later on to machine code) and C++ is translated immediately to machine language.

Answer 3

It is also my observation that C# is significantly faster to compile than C++. One of the main reasons is of course templates that don't need to be in headers in C#, as there are no headers. But heavy use of templates (mostly any modern C++ library like Boost) is killing the compile time in C++.

Answer 4

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)