After the Jump

re: After the Jump

Eric Battalio — Tue, 05 Feb 2013 18:59:50 GMT

Update: Stephan (STL) talks about do/while in his latest Core C++ video on Channel 9. Check it out at channel9.msdn.com/.../Stephan-T-Lavavej-Core-Cpp-8-of-n.

re: After the Jump

grumpy — Fri, 01 Feb 2013 11:33:21 GMT

@ildjarn: another quite important point: sync_with_stdio does nothing for file manipulation. It disables synchronization of the *standard* streams (stdin/stdout/stderr), but for file streams, it makes zero difference. If you think that setting sync_with_stdio to false magically solves all the performance problems with iostream, it sounds like cargo-cult programming to me. You haven't investigated whether what you're doing actually has an effect, you're just assuming it makes teh problem go away. :)

re: After the Jump

Diego Dagum — Mon, 28 Jan 2013 21:59:56 GMT

Not a bad idea to count with concrete performance requirements before dropping a meant-to-be-used library in favor of another one, just because the latter is faster.

The risk otherwise is to overcomplicate an approach to get a benefit that could be more apparent than real.

re: After the Jump

grumpy — Sun, 27 Jan 2013 10:20:16 GMT

@ildjarn have you actually benchmarked this? Because every test I've made has showed iostreams to be monstrously slow (easily a 5x over stdio). Of course, often performance doesn't matter, and type-safety is very nice, but the iostreams API is also so, well, messed-up that I don't think safety is much of an argument for using it. There's far too much to trip you up, far too much you can get wrong. It's just not a very good library, and as far as performance goes, the half-arsed "let's not even *try* to make it fast" implementation certainly doesn't help. (In fairness, it's not just the MSVC implementation that's slow. The same can be said of GCC's. I haven't tested Clang's, but I wouldn't be surprised to see that perform like crap as well)

re: After the Jump

ildjarn — Fri, 25 Jan 2013 22:47:53 GMT

> About reading a file using iostream. Don't. It is slower and difficult to manage for complicated file formats.

I could not disagree more. It's not (much) slower if you call `std::ios_base::sync_with_stdio(false)` first, and more importantly, it's *type-safe* – throwing away type-safety in C++ is the absolute last thing you want to do. If performance/complexity is that much of a concern, that's what Boost.Spirit is for . :-]

(And I know people will be inclined to balk at Spirit as a solution to complexity, but don't bother – after the initial learning curve, it's extremely easy to maintain very complicated file formats, both generation and parsing, and the runtime performance is unparalleled.)

re: After the Jump

Xiang Fan — Fri, 25 Jan 2013 17:05:57 GMT

One possible reason (implicit flush) for slow iostream:

blogs.msdn.com/.../speed-up-iostream.aspx

re: After the Jump

Eric Battalio — Fri, 25 Jan 2013 16:22:18 GMT

Andrew, stdio.

re: After the Jump

Andrew — Fri, 25 Jan 2013 01:13:24 GMT

What will you use instead of iostream?