4 ms·

> although I would still be surprised if Java is faster on a comparable-sized project Presumable I should really do a side by side comparison for a project of

> although I would still be surprised if Java is faster on a comparable-sized project Presumable I should really do a side by side comparison for a project of the same LOC but I always had the subjective feeling > You may have an include file that gets touched/changed a lot I more meant an initial clean&compile step > "pre-compiled header" option what do you mean here? > Finally, check to see whether you're doing a very aggressive "release" build, ok, this could be one cause, yes

dmlorenzetti 15y ago
what do you mean here? ("pre-compiled header") I don't know all the details, but consider that the compiler has to read the header file, parse it, make a map of its contents (its declarations and #defines and type definitions and so forth). And it has to do that over and over, for every source file that includes that header. So if the compiler stashes away a binary representation of the contents of that header, then it can skip the slow bits of reading the text file and figuring out its contents and all. It only has to do that the next time you change the header. edit: See http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html Java, I believe, essentially does this already, because it turns each .java file into a .class file (or whatever, it's been a while). And that .class file contains all the information that other java sources need in order to know what's in that java file. Fortran-90, a language that gets no love on Hacker News, has a nice module facility that also enables this. Module information can get stored in a binary form that other sources can look into without having to re-parse the original text file. Going back to C/C++, though-- if your root problem is that you have big header files that appear everywhere and slow down the compilation of every module, then you may want to think about reorganizing your code to reduce dependencies. Pre-compiling the headers may remove one of your symptoms, but not the real cause of the problem.
- karussell 15y ago
  Thanks for your explanation!

dmlorenzetti 15y ago

what do you mean here? ("pre-compiled header") I don't know all the details, but consider that the compiler has to read the header file, parse it, make a map of its contents (its declarations and #defines and type definitions and so forth). And it has to do that over and over, for every source file that includes that header. So if the compiler stashes away a binary representation of the contents of that header, then it can skip the slow bits of reading the text file and figuring out its contents and all. It only has to do that the next time you change the header. edit: See http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html Java, I believe, essentially does this already, because it turns each .java file into a .class file (or whatever, it's been a while). And that .class file contains all the information that other java sources need in order to know what's in that java file. Fortran-90, a language that gets no love on Hacker News, has a nice module facility that also enables this. Module information can get stored in a binary form that other sources can look into without having to re-parse the original text file. Going back to C/C++, though-- if your root problem is that you have big header files that appear everywhere and slow down the compilation of every module, then you may want to think about reorganizing your code to reduce dependencies. Pre-compiling the headers may remove one of your symptoms, but not the real cause of the problem.

karussell 15y ago
Thanks for your explanation!