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. printf is a parser. The only programming contests Web 2.0 platform, Finding least difference between max and min value of all possible sets of numbers, Educational Codeforces Round 132 [Rated for Div. This does not seem like a good enough reason for a performance hit of 5x.
I ran this on Windows after compiling with VC++ 2013 (both x86 and x64 versions). > 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. The universe is a figment of its own imagination. I suspect that it defaults to true so that you don't have to worry iflegacy libraries write to stdout/cout or stderr/cerr. > Sometimes, I find code where the developers prefer to use printf/> fprintf, instead of ostream classes. (a) Both systems have to format the output somehow, (b) managean internal file/stream buffer and (c) pump out the result into a filehandle which in both of the cases is done via (f|)write I assume.And at that point it is the operating systems responsibilityto do it as efficiently as possible. Nonsense. The reason is, printf uses system locks while cout doesn't. This isa core reason to use streams: the type of a variable can be changed tosome customised type and the input/output code typically worksunchanged. Powered by Discourse, best viewed with JavaScript enabled. Writing code in comment? The answer shows different cases where cout might be faster than printf() but for most circumstances, printf() is faster. As you can see, using printf and then fflushing takes about 5 times less time than using std::cout. The templates can also be inlined, whereas printf is always a function call.
(Anything coming in C++0x?
If performance is an issue, IOStreams tend to perform rather badly.This is due not only to the internal handling and potential dependencyon stdio (in which case it cannot be faster than stdio), but also tothe overhead of the heavily object-oriented design of the wholelibrary. Whether youcreate the formatting objects on the fly or reuse them is up to you. Then do you think the current design of iostreams is okay, despitethe problems I mentioned above? 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++. the ability to have yourvalues printed within different strings e.g. Last update: 07.03.21. make the lettersappear on the console). You might change the formatdynamically via:
is there a good workaround with>> streams?> > Hmm -- I'm not sure if I understand that point. 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. 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. ), 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. [ See http://www.gotw.ca/resources/clcm.htm for info about ]. When a newline character is encountered, it flushes the IO buffer. Of one of code 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. A detailed article on Fast Input Output in Competitive Programming, This article is contributed by Ayush Govil. 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. > so I have some questions lying around:> > - is printf really faster than streams in most of cases? 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. 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. How to use getline() in C++ when there are blank lines in input? I decided to write a quick test program to get at least some idea of which techniques did what. > I know there are solutions such as Boost.Format, but I doubt if> that's just an extra layer of abstraction, adding the cost of parsing> the format string while not eliminating the cost of manipulating> the formatting flags (and of course the virtual function call). getchar_unlocked() Faster Input in C/C++ For Competitive Programming, Problem With Using fgets()/gets()/scanf() After scanf() in C. Differentiate printable and control character in C ? hi!
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 not *reorder*> the arguments for printf matching values always have to appear in the> order given within the format string. They're not standardized, so everyone's inventing their own wheel, and it's a waste of time both to write them individually and to understand each other's. 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
Suppose you're printing a table, where each column has its own format [a very common situation].
Some ostream implementations use printf (sprintf) internally, perhapsfor consistency reasons - but I'm not sure about that.So for these implementations ostreams can't be faster than printf.My impression is that many implementations of iostreams, stringstreams,fstreams etc. 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. Using ostreams the formatting getspretty unreadable. I also don't really know if last thing i said is true. Can somebody plase explain that to me? They also support locales and code 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.
C++11 got the two first.
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.
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 :). How to print size of array parameter in C++? supposed to mean? Improve Your Code's Runtime with the Right Order of IF Statements or Using Switch Statements, http://codeforces.com/contest/436/submission/6890816. It's notvery hard to write one, and I also have done that. Also see below. If you write these 2 lines in the beggining of your code: will make cin faster than csdtio. > []Another issue for me is readability. I always thought printf is faster than than cout. Not to mention that
No. Hello everybody i have a question for you. thanks!). Or wait -- yes you *are* allowed to change the order without anypenalty of the great god of C-Programming, but then yourprogram dumps out junk or even crashes trying to interpret aninteger as a string address, and that AFAICT is the main reason that(f|)printf is said to be *evil*.
Anyway it's true that '\n' is much faster than endl. Please have a look at these two solutions, the code using cout is accepted but the code using printf is giving TLE. So dependent on the argument i n will be printed as a hex valueor a dec value. > > 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? I saw some people claim cout is faster than printf in some cases and i wondered if it's true. -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. So, cin wastes time synchronizing itself with the underlying C-librarys stdio buffer, so that calls to bothscanf()and cin can be interleaved. Dynamic Memory Allocation in C using malloc(), calloc(), free() and realloc(), Fast Input Output in Competitive Programming, Like with all things, there is a caveat here. It can be done inexpensively and I believe that results could be muchfaster than the current iostreams. Someone can> argue: if programs are not using the feature of mixing the two, they> shouldn't be forced to pay for it, either the synchronization overhead> or the explicit function call to turn it off; only those using the> feature should be required to do something explicitly. This works both ways, which is why hitting
> I suspect that a significant portion of C++ programs do not bother to> call sync_with_stdio(false), while not mixing stdio and iostream at all.> I wonder, doesn't this violate the zero-overhead rule?
Such problem is accompanied with Warning: large I/O data. That may not the greatest frustration, but a greatannoyance that you encounter often, here and there. 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. > - b) is a very strong issue! 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.
In addition, doesn't the iostream library also incur the overhead ofa virtual function call for every character read or written? In pretty much all cases I know if, it's not. The real question is: is this where you're slow? is there a good workaround with> streams? C++20 finally finally got the last one also with signed result, named std::ssize.
Press question mark to learn the rest of the keyboard shortcuts, https://ayandas.me/blog-tut/2019/04/06/speeding-up-iostreams-in-c++.html. 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.
Re convenience and re-ordering, only certain printf() implementations(e.g. 2], Recovering a linear recurrence with the extended Euclidean algorithm, Lexington Informatics Tournament 2022 (Registration Open! 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.
I tried it myself and cout is around 3 percent faster, In actual implementations printf is generally faster than cout <<, because. @rashedcs printf is definitely faster than cout because of internal syncing / flushing in iostream i/o which normally slows down their performance. Which one do you think is better: std::ostream& operator<<(std::ostream& os, const VirtualTime& t); Effects: prints the virtual time t into os (in such and such format). What is the reason for this? Such an approach can be emulated today but inefficiently and withoutremoving the cost of all the unnecessary iostream cruft. @rashedcs if you want to make cin cout faster just add this line in your code without quotes: here is an interesting record. 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. Now, there does appear to be one basic difference: you'd (apparently)like to create a formatting object on the fly, feed it all theformatting flags, have it format an object, and then destroy thatobject. Effects: prints the virtual time t into os (in such and such format). I've never heard that before, I'd be very interested if that was true though and why it is.. 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. It's usually quite a lot slower, in fact (usually around 200~300% slower at run-time). I do not see why c++ streams would be slower than cstreams: I/O are very slow operations per se.
My impression is that many early streams implementations got to thestage where they knew the precision and width and needed to put itinto the stream, so they used an sprintf("%*. I saw some people claim cout is faster than printf in some cases and i wondered if it's true. GNU). Yes the problem is that cout is synchronized with printf, which slows it down a ton. However using iostream with sync_with_stdio(false) makes i/o operations comparable to scanf/printf. but right now, I have to disagree about the I/O boundness argument(what about sprintf versus stringstream, for example?). Get access to ad-free content, doubt assistance and more! I think the current design could be improved, but what's he's advocatedlooks to me like it'd do more harm than good. By using our site, you The code in your program is the only thing that can change> them. 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. and cin becomes faster than scanf() as it should have been. The most generic answer I couldgive is that it is implementation dependent, but I don't see any particularperformance bottleneck in either of them. But its very important to use "\n" instead of endl for newline!!! I'm a firm believer that almost every class should bestreamable too very useful for test cases, debug trace, etc.. My major complaints about the iostream library are: 1.
"s (without using endl) takes about - You might change the format> dynamically via:>. Due to the locks being used by printf, on a large scale, the printf takes more time when compared to cout.
Recent changes: Fixed OP usages of tokens readme, I wrote an entire blog post about this. The moment you do this, you have basically nothing more or less than amediocre imitation of the current iostreams architecture -- i.e. 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. >> - b) is a very strong issue! It alsointimately bound to the streambuf (usually it outright owns it). > Your alternative is certainly a viable possibility, but you should be> aware that, > while it's _typical_ to create a stream and allow it to create a> stream buffer, it's entirely possible to create a stream buffer, then> attach stream objects to that stream buffer as you see fit, each (for> example) with a separate set of format flags, Well try it and see if it works. are pretty slow, compared to their C counterparts. 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). Summary of the answers: if you want to avoid tricky solutions, simply stick with cout but don't use endl since it flushes the buffer implicitly (slowing the process down).
It will call something more like fwrite. I've always heard the exact opposite, that printf is faster. if the format string is available for them. 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.
Don't get me wrong: overall, I tend to view modality as a shortcoming,and I prefer to avoid it in general. printfis faster compared to coutmostly unless you have turned off the sync in which case both are at par. Do you have any sources for your claim? 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 problem is that this formatting class isgeneral rather than specific to the class being formatted. 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.