Templates - efficiency and implementation

Ben Sizer · 2001-01-05T08:05:31

Ok, I am getting more and more disillusioned with templates the more I use them. Yes, things like the Standard Template Library give me a lot of efficiency in terms of how quickly I can implement things? But at what cost? Firstly, compile times. A simple C/C++ file with just ''C'' features, maybe the odd inherited class or two, compiles very swiftly. Throw a templatized list in there, or a map, and it starts taking 2 to 5 times longer. The amount of include files is probably a major culprit too: if I wish to use a STL list, including the "list" header in turn includes the "cstddef", "functional", "iterator", "memory", "stdexcept", and "xutility" headers, which in turn includes "stddef.h", "xstddef", "utility", "xmemory", "exception", and "xstring"... etc. A lot of these included files are just template functions that are there just in case I use them, which a lot of the time, I won''t. Secondly, executable/object file size. If I use an STL list, for example, it has to create a new instantiation of the code for every different type that uses it. Even if they are completely equivalent, eg. int* and char* behave exactly the same way in terms of storing them in a container class. You are just manipulating blocks of 4 bytes, essentially. Technically, certain parts of a template class can be shared (eg, where the functionality doesn''t depend on the type) which could reduce the amount of duplicated instantiation that goes on... ... but this is surely made irrelevant by the fact that the STL template code is all inlined in the classes, so it is almost certainly all just expanded inline in your code. Every single push_back() and pop_front() and remove() is getting expanded inline, for every use of the function, no matter whether it''s the same type and could therefore share the implementation. In every single file that uses it. A program with only 12 lines of code in a single function (main), that includes the "map", "string", and "iostream" headers is 120kb in release build. Expanding to almost 10k per line of my high-level-language. Doesn''t that seem a bit much? And if I wanted very similar functionality in a different source file, all the identical code appears to get re-inserted there too. If the code gets too bloated, then the benefits of inlined code start to get outweighed by the problems of having too much code for the cache to hold at once. Maybe it would be worthwhile just making an "stl.h", including every single STL header, and precompiling it? Is there some other way I can wrap these classes or otherwise use them that will let me use their functionality as function calls rather than inline expansions everywhere throughout my code, duplicating functionality a billion times? And, perhaps more importantly to me, cut my 35 minute rebuild times to a more manageable 10 minutes or so? I welcome opinions from those who are more knowledgable in compiler implementation and efficient template usage than myself, as I expect I have got some of my facts wrong... but who knows.

General and Gameplay Programming Programming

Started by Kylotan January 01, 2001 02:40 PM

31 comments, last by Kylotan 24 years ago

Stoffel

250

January 04, 2001 06:38 PM

quote: Original post by Kylotan

Wilka, here''s an example of the STL bug/issue I was talking about:
compiled in MSVC5.0:

Works fine with MSVC5 and MSVC6 with the latest respective service packs . MSVC had severe known bugs with templates period (nothing to do with STL specifically) in their initial releases. The service packs fix most of the bugs. There are still some bugs, as I understand, with templated members--haven''t run into any myself. But I use STL extensively and haven''t had a bug yet. In fact, MSVC''s STL is more standard compliant than gcc''s STL.

I''ve been interviewing a lot of recent graduates lately and have found that most computer science programs (bachelor''s and master''s) seem to be using STL. It''s just a matter of time before the population at whole adopts this newest part of the C++ standard. But of course, you should always know your compiler--no compiler is without bugs or limitations, at least not yet.

Void

126

January 04, 2001 07:52 PM

Kylotan:

Are u building static libs of common classes so that you don''t have to compile them when you do a full rebuild.

Kylotan

Author

10,513

January 05, 2001 08:05 AM

Void: Makes no difference whether they''re static libs or not. I only ever rebuild the stuff that needs rebuilding.

Stoffel: I can''t apply the service packs cos I have the cheap version of MSVC5. Oh well.

Wilka: I dunno anything about custom build steps... would I have to set that up on a per-file basis? Would it be feasible to instead write a DevStudio macro to compile using Borland?

*sigh* And Visual C++ was the only Microsoft product I liked, too.

Templates - efficiency and implementation

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Templates - efficiency and implementation

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines