Using ostreams the formatting getspretty unreadable. However: 1. Not really. That's the reason such librariesuse placeholders like '%1''%5' in their format string insteadof '%d' '%s'. Last update: 07.03.21. Formatting flags are persistent, so writing a I/O subroutine often involves saving the formatting flags at the beginning and restoring them at the end. When a newline character is encountered, it flushes the IO buffer. This makes the "current" formatting properties stored in the iostreamobject pretty useless. You maybuild up a whole collection of classes/functions/operatorsworking on a std::basic_ostream & andwork on std::cout for months and afterwards you writeyour own sublass of basic_ostream<> and the outputends up in a window, a database or as an outputstream of a web application. It's tedious and verbose to set the formatting flags: compare (a) printf("%6.4f", x);vs (b1) std::cout.setf(std::ios_base::fixed, std::ios_base::floatfield); std::cout.precision(4); std::cout.width(6); std::cout << x;or (with ) (b2) std::cout << std::fixed << std::setprecision(4) << std::setw(6) << x; (not counting restoration of the flags). When you unsynchronize the two, now you have to flush explicitly. many say that printf is actually faster than cout, but the reality is the reverse. while it's _typical_ to create a stream and allow it to create astream buffer, it's entirely possible to create a stream buffer, thenattach stream objects to that stream buffer as you see fit, each (forexample) with a separate set of format flags, and 2) that your setup islikely to require careful design to get good efficiency -- inparticular, since you're likely to create and destroy a lot offormatting objects, you need to be sure doing so is fairly inexpensive. If you have so little idea of what's happening in your program> that something might produce output without knowing what formatting is> currently in effect, then you have a _serious_ problem in your program,> that has nothing whatsoever to do with the design of iostreams. By using our site, you Printf is faster. By contrast, the iostreams classes are designed so theformatting object is more more permanent, and with at least somecapability to store formatting information in the longer term. Astream should know how to output character sequences and some kind of'sequence producer' only. No. And it's not type safe, and it's not locale aware. for example, format strings allowsreording of the arguments (their order is hardcoded using streams).this ease the application deployment. These two problems can be largely solved by helper classes that savethe formatting flags at construction, set them as specified by theclient, do the I/O, and restore the flags at destruction. I doubt that this is a reasonable argument. If you have so little idea of what's happening in your programthat something might produce output without knowing what formatting iscurrently in effect, then you have a _serious_ problem in your program,that has nothing whatsoever to do with the design of iostreams. (Anything coming in C++0x? Yes the problem is that cout is synchronized with printf, which slows it down a ton. That's misleading at best -- it's only changed whensome part of your program changes it. An output stream should be something that knows only to outputsequences of characters. The direct answer is that yes, that's okay. An ideal output wouldgo along the lines. I also don't really know if last thing i said is true. getline() Function and Character Array in C++. Another thing speaking for iostreams is the fact, thatit can be much more then just a file/terminal. In contrast, if you insert an_int or a_double into a basic_ostreamwithout any format specification, you never know how the numbers willbe formatted: an_int may be in decimal or hexadecimal or whatever,a_double may be general, fixed, or scientific, with an unknown precision,both with an unknown amount of padding, because you never know whatthe previously called functions might have set for the stream (exceptwhen you do know :D). supposed to mean? On the count of speed though the reputation is well earned with manyimplementations.The TR on C++ performance (http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf) has a detailed description.We once noticed a considerable performance difference between visual c++ 2005 iostreams and both qt's stream implementation or printf basedreading when reading large files. Such an approach can be emulated today but inefficiently and withoutremoving the cost of all the unnecessary iostream cruft. However using iostream with sync_with_stdio(false) makes i/o operations comparable to scanf/printf. If a state saving class is the answer, I'd like to see one standardizedat least so that I don't have to export and explain mine from my toolbox or try to understand others' every time. I'm curious, how did you do your benchmarks? In addition, doesn't the iostream library also incur the overhead ofa virtual function call for every character read or written? I believe that the formatting isought to be bound to the object rather than the sink. So dependent on the argument i n will be printed as a hex valueor a dec value. Why is scanf faster than cin?On a high level both of them are wrappers over theread() system call, just syntactic sugar. ios_base::sync_with_stdio(false); cin.tie(0); http://lmgtfy.com/?q=ios_base+sync+with+stdio+0, try the same with second one :) there's a lot of information in internet, so search for it and read it :). Output of above program when dummy file is redirected to stdin. but right now, I have to disagree about the I/O boundness argument(what about sprintf versus stringstream, for example?). On running this program, one gets to know the working of printf is lock inclusive and cout is lock exclusive. is there a good workaround withstreams? Feel free to skip the initial Python and Java portions: https://ayandas.me/blog-tut/2019/04/06/speeding-up-iostreams-in-c++.html. Do you have any sources for your claim? Effects: prints the virtual time t into os (in such and such format). So my idea is to mix the two printing methods: I want to use cout for simple prints, and I plan to use printf for producing huge outputs (typically in a loop). Standard IO streams are templates, they're type safe, and type and size of parameters are decided at compile time, so that is where most of the runtime performance edge comes from. for example, format strings allows>> reording of the arguments (their order is hardcoded using streams).>> this ease the application deployment. Thats also a library. That's exactly how things work now, except that the names are different.A stream buffer knows only about reading/writing streams of characters.A stream is a formatting class that's attached to a stream buffer thatacts as its source or sink -- but all the stream itself does isformat/parse data going to/coming from the stream buffer. Nonsense. [ See http://www.gotw.ca/resources/clcm.htm for info about ]. if the format string is available for them. I tried it myself and cout is around 3 percent faster, In actual implementations printf is generally faster than cout <<, because. I decided to write a quick test program to get at least some idea of which techniques did what. In pretty much all cases I know if, it's not. That may not the greatest frustration, but a greatannoyance that you encounter often, here and there. Do you really want to keep in mind that the state of os is changedafter you print a VirtualTime object into os? thanks!). If I remember correctly cout is almost always slower than printf due to some buffer synchronisation it does to ensure order of output. Except it also consults locale to do the conversion. The argument for printf that formats a long, Correct format specifier for double in printf, C++ What are the basic rules and idioms for operator overloading, C++ printf more than 5 times faster than std::cout, C++ the printf format specifier for bool, C++ Why does GCC generate 15-20% faster code if I optimize for size instead of speed, C++ Why does C++ code for testing the Collatz conjecture run faster than hand-written assembly, printf/puts are much faster than cout when writing to the NUL device, but cout keeps up quite nicely when writing to a real file, Quite a few proposed optimizations accomplish little, In my testing, fill_n is about as fast as anything else, By far the biggest optimization is avoiding endl, cout.write gave the fastest time (though probably not by a significant margin. Or do you have any other approach to> solve the problems in mind? The only issue I had with iostreams - related to performances - waswhen I forgot to call sync_with_stdio( false ) on my C++ streams andsuffered a penalty hit (do not know if this still stands today) usingsome vendor lib. some_stream << setprecision(4) << foobar(); > 2) that your setup is> likely to require careful design to get good efficiency -- in> particular, since you're likely to create and destroy a lot of> formatting objects, you need to be sure doing so is fairly inexpensive. an implementation that implements C++ streams in terms of the C streams can't be more efficient than the C streams, and will generally add overhead. Side effects: sets std::ios_base::fixed, width 8, precision 4 on os. Even if it's some part of my program, there can be a lot of them sincemost I/O routines are included, and the fact stays the same that I don'twant to be distracted by side effects they cause. The moment you do this, you have basically nothing more or less than amediocre imitation of the current iostreams architecture -- i.e. 90ms for printf(), 79ms for cout. Please have a look at these two solutions, the code using cout is accepted but the code using printf is giving TLE. So now you know why everyone using printf willburn in hell ;-). "s (without using endl) takes about - > > Quite the contrary: you've advocated virtually nothing that's not> > already available via iostreams, but your idea:> > 1) has a poorly defined architecture, mixing some formatting> > responsibility into the buffer class.> > 2) will require very careful design to avoid even worse efficiency from> > the number of formatting objects you create and destroy.> > Then do you think the current design of iostreams is okay, despite> the problems I mentioned above? Which is probablythe wrong place to do this kind of stuff. where can I, >> In contrast, if you insert an_int or a_double into a basic_ostream, http://www.open-std.org/jtc1/sc22/wg21/docs/, 13d312b60@p10g2000prf.googlegroups.com, http://kanze.james.neuf.fr/doc/en/IO/html/. a subreddit for c++ questions and answers, Press J to jump to the feed. First you have the overhead ofcreating a general stream object with all its bases and information.Then by default streams assume that they own the buffer. I've never heard that before, I'd be very interested if that was true though and why it is.. Producing these sequences from objects andfeeding them into a stream should be left to a separate formattinglibrary (that's also where locales should live). I know that it's implementation dependent, but on my Linux box printf is 8x faster. You do not have permission to delete messages in this group, Either email addresses are anonymous for this group or you need the view member email addresses permission to view the original message, Sometimes, I find code where the developers prefer to use printf/, > - is printf really faster than streams in most of cases? And they come up with things like this: QString("Processing file %1 of %2: %3").arg(i).arg(total).arg(fileName);. printfis faster compared to coutmostly unless you have turned off the sync in which case both are at par. What is the line. I do not see why c++ streams would be slower than cstreams: I/O are very slow operations per se. Powered by Discourse, best viewed with JavaScript enabled. for internationalization.that's a big issue and if for example you look at the effort librarieslike Qt take in QString::args I think there really isn't an easy solution.and (f|)printf doesn't help you much since different languages needdifferent ordering for their args. Most of my programs clear the execution time limit, mostly 3 seconds or 5 seconds, on online compilers when using scanf/printf which exceeded the limit while using cin/cout. 5.std::cout test: 1.108 s ; printf test: 0.232 s Can anyone help me with the better solution O(n^3) for this Problem ? It can be interesting if you produce large outputs. How to use getline() in C++ when there are blank lines in input? Also, only certain printf() implementations allow you to supplementthe conversion specifiers (e.g. They also support locales and code conversion. you'vetaken the current architecture, but rather than its clean separation offormatting from buffering, you advocate something that's supposed to bea buffer, only it knows about _some_ default formatting > Such an approach can be emulated today but inefficiently and without> removing the cost of all the unnecessary iostream cruft. The templates can also be inlined, whereas printf is always a function call. > An ideal output would>> > go along the lines>> > cout << format("08x", an_int)> > << " "> > << format(".2", a_float)> > << format(foobar())> > << format("my_custom$3$", foobar());>> > This doesn't preclude simple cout << 1; usage but it has to be defined> > in terms of some default format().>> The moment you do this, you have basically nothing more or less than a> mediocre imitation of the current iostreams architecture -- i.e. >> - b) is a very strong issue! Let us compare the time taken to read the file from stdin (get the file from disk to stdin using redirection) by using scanf() versus cin. This works both ways, which is why hitting flushes input to cin (you can cause an explicit flush in Windows with or on *nix with ). What do you think? It can be done inexpensively and I believe that results could be muchfaster than the current iostreams. But i saw printf and ither printf-like functions defined in linux kernel. Isn't all output streams converted to printf, because that's what operating systems support? 2], Recovering a linear recurrence with the extended Euclidean algorithm, Lexington Informatics Tournament 2022 (Registration Open! A lot of people have thrown around various ideas of how to improve speed, but there seems to be quite a bit of disagreement over which is most effective. It's notvery hard to write one, and I also have done that. Therefore it isnt much useful to switch from one to another, just because its slow. No this is not the real difference. Of one of code You might change the format> dynamically via:>. > Sometimes, I find code where the developers prefer to use printf/> fprintf, instead of ostream classes. I also don't really know if last thing i said is true. The code in your program is the only thing that can change> them. However C++ streams have the technical potential to be faster. If you care about the formats, you have to do something: either havethe subroutines revert to the old state every time after changing it,or don't depend on the current state and set every flag you care aboutbefore any I/O. printf is also Turing Complete, FYI. are pretty slow, compared to their C counterparts. You snipped the beginning of my post which argued that howto format an object is a property of the object rather than somegeneral formatting class. You can not *reorder*> the arguments for printf matching values always have to appear in the> order given within the format string. The only performance penalty I see is that printf has to parse theformat string, while the current output format (setprecision, hex,dec etc.) hi! is there a good workaround with>> streams?> > Hmm -- I'm not sure if I understand that point. > - b) is a very strong issue! I've encountered the same doubt about 5 years ago and found an answer in OS perspective and I even discussed it with my professor then, for a healthy argument to arrive at a conclusion.

You can use some flags to disable it and it would perform as fast as printf. A detailed article on Fast Input Output in Competitive Programming, This article is contributed by Ayush Govil. Even printf is reduced to system calls that copy bytes into buffers, and flag the associated file descriptor that there are bytes ready to read at the destination. Producing these sequences from objects and> feeding them into a stream should be left to a separate formatting> library (that's also where locales should live). See James Kanze's formatting classes *Fmtand StateSavingManip at ,for an example of approach (2). It is true that some parts are modal, and it's not at all obvious rightoff what's modal and what's not, or why some particular things are modalor others aren't. !.std::cout test: 1.125 s ; printf test: 0.195 s It'sjust a string and an integer. Hmm -- I'm not sure if I understand that point. for example, format strings allows. The answer shows different cases where cout might be faster than printf() but for most circumstances, printf() is faster. It will make no difference mostly, but you could consider using '\n' instead of std::endl. I haven't seen the rationale behind the decision to make the flagspersistent, but I suspect that it was caused by the limitation of thebinary inserter/extractor syntax, the inability to supply formattingspecification together with the data, and I wish there had been abetter way to solve it. printf() and streams shouldbe I/O bound, I would guess that the execution time of the call itselfis irrelevant compared to the time to do the I/O (e.g. They're synchronized with stdio, which is a performance penalty in order to: A) Get line buffering, especially for output, B) Interleave with stdio, so you can mix printf and cout. Nonetheless, its real effects inthe case of iostreams are pretty minimal at worst. //use this in Linux environment, feel free to change the size to a larger value, #include #include #include void function_cout(){std::cout<<"This printing is being done by 'cout'"< An output stream should be something that knows only to output> sequences of characters. It shouldn't. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. ), Ultimate Topic list (by YouKn0wWho) with filters on Difficulty, categories and topics, An interesting computer game - Aircraft War, Solution to problem M. Algoland and Berland of 2018-2019 ICPC, NEERC. > Now, there does appear to be one basic difference: you'd (apparently)> like to create a formatting object on the fly, feed it all the> formatting flags, have it format an object, and then destroy that> object. It does not mean that OO alone makes it slow, but certainlythere are places where virtual function calls prevent compilers fromdoing some optimizations that would be otherwise quite easy. Saving and restoring formatting flags are often wasteful, because you'll be setting another flag after restoring them anyway. @rashedcs printf is definitely faster than cout because of internal syncing / flushing in iostream i/o which normally slows down their performance. The reason is, printf uses system locks while cout doesn't. Effects: sets std::ios_base::fixed, width 8, precision 4 on os, and prints the virtual time t into os. I know there are solutions such as Boost.Format, but I doubt ifthat's just an extra layer of abstraction, adding the cost of parsingthe format string while not eliminating the cost of manipulatingthe formatting flags (and of course the virtual function call). Consider afoobar class that doesn't have any notion of 'precision' for itsformatted output. Moving the format string to a global array, and passing that as the format string produces identical output, but forces it to be produced via printf instead of puts. > so I have some questions lying around:> > - is printf really faster than streams in most of cases? In general, streams have the advantage ofknowing the types at compile time, so can be faster. I'm sharing it here as I feel it'll be useful. Or you can use boost::format, which works with streams andstd::strings, for example like this: cout << boost::format("writing %1%, x=%2% : %3%-th try") % "toto" %40.23 % 50; Of course you won't get Qt's very good i18n features. Don't get me wrong: overall, I tend to view modality as a shortcoming,and I prefer to avoid it in general. If you write these 2 lines in the beggining of your code: will make cin faster than csdtio. Such problem is accompanied with Warning: large I/O data. I assume this is asking for a flame war, where people claimthat their implementation of vendor X on platform Y is much moreperformant with (iostream|printf). Of course, it's possible they might optimize around this some day as well, but at least for now (g++ 5.1) a test with g++ -O3 -S confirms that it's actually calling printf (where the previous code compiled to a call to puts). Anders Kaseorg was kind enough to point out--that g++ recognizes the specific sequence printf("%s\n", foo); is equivalent to puts(foo);, and generates code accordingly (i.e., generates code to call puts instead of printf).

Can somebody plase explain that to me? > A stream is a formatting class that's attached to a stream buffer that> acts as its source or sink -- but all the stream itself does is> format/parse data going to/coming from the stream buffer. std::ios::sync_with_stdio(false);, Ive made some programs and saw that scanf and printf are considerably faster than using cin and cout? the ability to have yourvalues printed within different strings e.g. guess now i understand what you mean. Someone canargue: if programs are not using the feature of mixing the two, theyshouldn't be forced to pay for it, either the synchronization overheador the explicit function call to turn it off; only those using thefeature should be required to do something explicitly. Isincerely hope modern streams implementations have at least ripped offthe *printf() implementation to inline it, and hopefully optimised ita bit in the process. Use "\n" instead. So the usage of locks makes the printf take longer time than the cout. I don't mean I have no idea of what's happening, but do you really wantto keep track of the details of formatting flag changes that happen asyou call subroutines?

acknowledge that you have read and understood our, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Find a pair of overlapping intervals from a given Set, Count substrings consisting of equal number of a, b, c and d, Program to reverse a string (Iterative and Recursive), Print reverse of a string using recursion, Write a program to print all permutations of a given string, Print all distinct permutations of a given string with duplicates, All permutations of an array using STL in C++, std::next_permutation and prev_permutation in C++, Lexicographically Next Permutation in C++. ]. so I have some questions lying around: - is printf really faster than streams in most of cases? And if were not mixing cstdio and iostream, we can turn it off, and then iostream is fastest. An ideal output would> go along the lines> > cout << format("08x", an_int)> << " "> << format(".2", a_float)> << format(foobar())> << format("my_custom$3$", foobar());> > This doesn't preclude simple cout << 1; usage but it has to be defined> in terms of some default format(). where can Ifind more info about that? Isn't all output streams converted to printf, because that's what operating systems support? generate link and share the link here. The difference between their execution time is not big enough to cause worries if your algorithm is working properly. Please have a look at a simple replacement library that has beendesigned specifically to allow aggressive compiler optimizations.Performance charts are included further down the page: > b) the ability of quickly replacing the format string, --Maciej Sobczak * www.msobczak.com * www.inspirel.com. Whether youcreate the formatting objects on the fly or reuse them is up to you. Really? To be sure of the formatting used, you shouldeither: (1) set every relevant formatting flag explicitly, at leastafter calling a stream I/O function, or (2) conform to the requirementthat every stream I/O function should save the flags at the beginningand restore them at the end. While you can probably makeit work it misses the whole point. Agreed but IMHO these are just a manifestation of a larger problem.Formatting information is not a property of a stream and, in general,a stream has no business doing any formatting at all. > []Another issue for me is readability. If the iostreams classes are intended to be the way they are now,that's too bad. I saw some people claim cout is faster than printf in some cases and i wondered if it's true. Having to modify "%d", x to "%s", x.str() everywhere istedious.

4.std::cout test: 1.322 s ; printf test: 0.221 s You should benchmark it yourself. GNU). The universe is a figment of its own imagination. The operating system merely supports outputting a single character or a line of characters. Secondly http://codeforces.com/contest/436/submission/6890816 scanf is faster than cin, but i guess printf is slower when it comes to long long int. With the -Wall flag gcc warns me that I'm doing he wrong thingwhen trying this: But I think that's just pure luxury and not part of the standard.And it fails if I provide the format string as a variable. What do you think? You have a couple of arguments whichare semantically linked (the %d and the n in the example above)but printf does not force you to respect this semantics. I think you completely misunderstood what I meant by example above. Regular competitive programmers face common challenge when input is large and the task of reading such an input from stdin might prove to be a bottleneck. I ran this on Windows after compiling with VC++ 2013 (both x86 and x64 versions). The meaningless. Due to the locks being used by printf, on a large scale, the printf takes more time when compared to cout. Your alternative is certainly a viable possibility, but you should beaware that 1) it's primarily a difference in degree rather than kind --i.e.

But its very important to use "\n" instead of endl for newline!!! is stored within the iostream in a more appropriate wayfor the CPU to understand. Let us create a dummy input file containing a line with 16 bytes followed by a newline and having 1000000 such lines, making a file of 17MB should be good enough. I suspect if C++ streams are faster it's because it doesn't have to unpack the format string to figure out how to extract the varargs stuff from the stack. I have an answer to this!

Improve Your Code's Runtime with the Right Order of IF Statements or Using Switch Statements, http://codeforces.com/contest/436/submission/6890816. C++11 got the two first. It doesn't need to know anything about *any*default formatting. Also see below. for example, format strings allows> reording of the arguments (their order is hardcoded using streams).> this ease the application deployment. ), 2. Nonetheless, its real effects in> the case of iostreams are pretty minimal at worst. and cin becomes faster than scanf() as it should have been. printf deals with less complex locale machinery, by default the C++ streams are synchronized with the C streams, which adds enough overhead that it's possible to turn that off, and. for security reasons, I want to get rid of type-unsafe printfphilosophy. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. It may not be that expensive (especially compared to the actual I/O cost), and compilers really good at optimization could get away with even that, but I doubt such are very common, and it makes me uncomfortable anyway. How to print size of array parameter in C++? So, cin wastes time synchronizing itself with the underlying C-librarys stdio buffer, so that calls to bothscanf()and cin can be interleaved. But may be there are even optimizationsavailable for the parsing step. Anyway it's true that '\n' is much faster than endl. The only visible difference is that scanf() has to explicitly declare the input type, whereas cin has the redirection operation overloaded using templates. It's not portable. 3450ms for printf(), 3420ms for cout. It depends on which operating system u are using, but actually it doesnt make much difference. make the lettersappear on the console). scanf printf