C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  STL and Software Drivers          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message rajanikanth@gmail.com Guest Posted: Wed Jan 19, 2005 11:23 pm    Post subject: STL and Software Drivers hi! Could somebody tell me if STL(Standard Template Library) can be used for writing software drivers. Most people told me that it wont be as efficient as C language. Thanks, Raj [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Thu Jan 20, 2005 6:13 pm    Post subject: Re: STL and Software Drivers [email]rajanikanth (AT) gmail (DOT) com[/email] wrote: Quote: Could somebody tell me if STL (Standard Template Library) can be used for writing software drivers. I suspect that it depends on the driver, and the system. To tell the truth, I can't see much use for most of the STL in drivers; a basic driver just doesn't do that much. Quote: Most people told me that it won't be as efficient as C language. In what regard? There may be some restrictions, depending on the system; I can imagine systems in which operator new can't be used in an interrupt service routine, for example, or even that it cannot be used in kernel level software (like a driver) at all. In such cases, of course, any of the standard containers are out. On the other hand, I would imagine that most of the time, the standard algorithms are at least as fast as their C counterparts, if not faster. -- James Kanze GABI Software http://www.gabi-soft.fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top msalters Guest Posted: Thu Jan 20, 2005 6:15 pm    Post subject: Re: STL and Software Drivers [email]rajanikanth (AT) gmail (DOT) com[/email] wrote: Quote: hi! Could somebody tell me if STL(Standard Template Library) can be used for writing software drivers. Most people told me that it wont be as efficient as C language. Sure. The STL is a Template library, which means that a lot of overhead is kept to compile time. E.g. std::sort is often faster then C's qsort, because the sort order can be detected at compile time. In C, qsort only gets a function pointer, which is much slower on typical CPUs. A speedup of a factor 6 has been reported going from qsort to std::sort. Another good example is std::string. Modern std::string implementations are a lot better than malloc(), for a number of reasons: better locality than a char*, no alignment overhead ( malloc() usually needs to return 4 or 8byte aligned memory ), no heap access for small strings. So, C++ can be more efficient than C. In fact, C is almost a subset of C++, so it's very likely it will be more efficient if used by a good C++ programmer. But just like C, C++ is not a very forgiving language - especially if efficiency matters. ( a C programmer who changes char*s into std::string*s instead of std::strings will see no speedup. ) Regards, Michiel Salters [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Darren Bane Guest Posted: Thu Jan 20, 2005 6:51 pm    Post subject: Re: STL and Software Drivers This question is almost off-topic. The answer totally depends on your operating system. For Mac OS X, drivers _must_ be written in C++, but I think it's the Embedded C++ subset, which doesn't have the STL. For embedded systems, where most of my experience is (VRTX & VXWorks), I'm not sure that I would recommend C++ at all for code which is coupled tightly with the kernel. A C++ runtime assumes the existence of some facilities, like a memory manager, which may not be available to device drivers, and certainly won't be at system start-up time. I'd just copy what other people do on your platform. For instance, most UNIX drivers are written in C--you can read them in the source tree. In contrast, I think the idea with microkernel-based OSs is that your drivers are application programs, for which C++ is a fine (business, not technical) choice. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Allan W Guest Posted: Thu Jan 20, 2005 8:06 pm    Post subject: Re: STL and Software Drivers [email]rajanikanth (AT) gmail (DOT) com[/email] wrote: Quote: Could somebody tell me if STL(Standard Template Library) can be used for writing software drivers. Yes of course. If you can use C++ at all, and the compiler you're using supports templates, you can use STL. Quote: Most people told me that it wont be as efficient as C language. It all depends on what "efficient" means, and how you measure it. Embedded programmers often complain that any use of templates at all induces "code bloat." This is a controversial opinion, partly fueled by early compilers that didn't handle templates very well, and bad use of templates that failed to factor out the code that didn't depend on the template arguments. I don't want to trigger 1000 posts on whether templates cause "bloat" or not, so I'll point out that for much of the STL, this "bloat" is irrelevant. Most of the STL is optimized for speed, and one of the primary ways this is accomplished is through the use of inline functions. Sometimes inline functions actually produce LESS code than a call to an out-of-line function, but we all know that isn't the typical case. In many cases, expanding template code inline for speed is exactly what you want for drivers. On the other hand, depending on what kind of drivers you're writing and the OS you're writing for, you could have severe memory limitations -- the inline aspect of the STL could actually work against you. Also, nothing in the STL comes for free. The containers, for example, are very fast compared to alternatives I've seen, but additional features come at the cost of some overhead. As an obvious example, you'll find that vector is extremely fast, but there is some overhead to keep track of some things such as the current size and capacity, and the ability to grow automatically. Suppose your driver needs to access 27 Foo objects -- always exactly 27. In user code, I might recommend that you use a vector for this, but in driver code I would stick to a raw "C-style" array. That way the size can be a constant and you won't include any code that checks the current size before it does an access. I guess the bigger answer is that it depends on what you need to do in the driver. If the STL fills those needs, use it! If it's only close, you need to figure out if you can do better on your own. HTH. Good luck. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maxim Yegorushkin Guest Posted: Thu Jan 20, 2005 8:07 pm    Post subject: Re: STL and Software Drivers On 19 Jan 2005 18:23:26 -0500, <rajanikanth (AT) gmail (DOT) com> wrote: Quote: Could somebody tell me if STL(Standard Template Library) can be used for writing software drivers. Most people told me that it wont be as efficient as C language. It depends on how you use STL. STL containers and algorithms on their own do not impose much of performance waste. There are two main performance killers to consider: * memory allocation * data copy The first one can be avoided by not using STL containers or using them with a custom allocator that gets memory from a preallocated pool. Except containers, there are no memory allocations in STL (please note, that streams are not a part of STL, rather they are part of the standard C++ library). As for the second, you've got no control over how many copies of your objects are made inside containers and algorithms, although it's resonably to assume that the authors of an STL implementation put some effort to minimize them. But you do have control over your objects' implementation and you can make their copy operation cheap, or use pointers instead of objects just like you do it in C. -- Maxim Yegorushkin [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Sat Jan 22, 2005 5:02 am    Post subject: Re: STL and Software Drivers Allan W wrote: Quote: rajanikanth (AT) gmail (DOT) com wrote: Could somebody tell me if STL(Standard Template Library) can be used for writing software drivers. Yes of course. If you can use C++ at all, and the compiler you're using supports templates, you can use STL. Not at all. If you're writing device drivers, you are very definitly in a freestanding environment, and according to the C++ standard (§17.4.1.3), the presence of the STL is optional. Operator new and exceptions aren't. In practice, however, I imagine that on most systems, they won't work, or won't work correctly, in an interrupt handler. (An exception certainly shouldn't be allowed to propagate out of the interrupt handler. And if your library uses a system request to get the memory it hands out, I'd be very surprised that new works correctly in a device driver, regardless of what the standard says. -- James Kanze GABI Software http://www.gabi-soft.fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top wkaras@yahoo.com Guest Posted: Sat Jan 22, 2005 11:26 am    Post subject: Re: STL and Software Drivers [email]rajanikanth (AT) gmail (DOT) com[/email] wrote: Quote: hi! Could somebody tell me if STL(Standard Template Library) can be used for writing software drivers. Most people told me that it wont be as efficient as C language. Thanks, Raj If you need an associative container, I have written an AVL tree template that allows/requires the instantiation to contruct, destroy, and locate the nodes in memory: http://www.geocities.com/wkaras/gen_cpp/avl_tree.html I have also written equivalent templates for hash tables, doubly-linked lists, etc. (Did this on company time, so I can't make these public domain.) This AVL tree template does not throw exceptions. I don't believe there's anything inherent about exceptions that would make it impossible to use them in a driver. But the run-time code to support exceptions in a particular compiler implementation might allocate memory from the heap, or do something else you potentially can't do in a driver. So far, I haven't seen a C++ compiler that didn't come with an STL version that doesn't throw exceptions, so the exception issue is not a show stopper. Probably, you can use template in the STL that doesn't use the 'new' operator. If you're going to write kernel code in any language besides assembler, I'd suggest you not use any code unless you feel you could hand-translate it into assembler if you had to. The information you need to have this level of understanding is harder to come by for C++ than for C. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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