When you use "%d" or "%g" (without any further specification) in stdio,you know exactly how the output will be formatted: as a decimal integerand a general floating-point with the default precision, without anypadding. Do you have any sources for your claim? I am aware of this. 2], Recovering a linear recurrence with the extended Euclidean algorithm, Lexington Informatics Tournament 2022 (Registration Open! Nonetheless, its real effects inthe case of iostreams are pretty minimal at worst.

> 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. 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. In some Online Judge if we use cout , we get TLE but if we use printf we get Accepted. 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. getline() Function and Character Array in C++.

I have an answer to this! 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.

Another thing speaking for iostreams is the fact, thatit can be much more then just a file/terminal. ), 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. 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. It'sjust a string and an integer. Not to mention that often compiles 10~15 times slower than and has twice the binary overhead std:cout won't actually call printf. I've never heard that before, I'd be very interested if that was true though and why it is.. When a newline character is encountered, it flushes the IO buffer. It will call something more like fwrite. It's usually quite a lot slower, in fact (usually around 200~300% slower at run-time).

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 suspect that a significant portion of C++ programs do not bother tocall sync_with_stdio(false), while not mixing stdio and iostream at all.I wonder, doesn't this violate the zero-overhead rule? 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.

Please use ide.geeksforgeeks.org,

Anyway if you have right solution it doesn't matter if u're using cout or printf :), EDIT: Check this ( I've changed your solution so i can use int everywhere ), http://codeforces.com/contest/436/submission/6890858, http://codeforces.com/contest/436/submission/6890844.

Benchmarks don't lie, but the results are nuanced. I tried it myself and cout is around 3 percent faster, In actual implementations printf is generally faster than cout <<, because. 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.

With synchronization turned off, using, With synchronization turned off, the above results indicate that.

Streams aresimply not designed to be used this way. I also don't really know if last thing i said is true.

I suspect that it defaults to true so that you don't have to worry iflegacy libraries write to stdout/cout or stderr/cerr.

> 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? What do you think? if the format string is available for them. printf is a parser. many say that printf is actually faster than cout, but the reality is the reverse. > This makes the "current" formatting properties stored in the iostream> object pretty useless. And they come up with things like this: QString("Processing file %1 of %2: %3").arg(i).arg(total).arg(fileName);. Isn't all output streams converted to printf, because that's what operating systems support? Which is probablythe wrong place to do this kind of stuff. 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. 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.

That's misleading at best -- it's only changed whensome part of your program changes it. hi! 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 doubt that this is a reasonable argument. 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).

What? If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org.

@rashedcs if you want to make cin cout faster just add this line in your code without quotes: Such an approach can be emulated today but inefficiently and withoutremoving the cost of all the unnecessary iostream cruft. Using ostreams the formatting getspretty unreadable.

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.

GNU). is there a good workaround with>> streams?> > Hmm -- I'm not sure if I understand that point. 90ms for printf(), 79ms for cout. 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. 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. 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 :). Then do you think the current design of iostreams is okay, despitethe problems I mentioned above?

Improve Your Code's Runtime with the Right Order of IF Statements or Using Switch Statements, http://codeforces.com/contest/436/submission/6890816. Get access to ad-free content, doubt assistance and more! and cin becomes faster than scanf() as it should have been. > 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. You can use some flags to disable it and it would perform as fast as printf. guess now i understand what you mean.

It shouldn't. 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). The real question is: is this where you're slow? Or do you have any other approach to> solve the problems in mind? 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.

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. You can not *reorder*> the arguments for printf matching values always have to appear in the> order given within the format string. Powered by Discourse, best viewed with JavaScript enabled.

The meaningless. I'm sharing it here as I feel it'll be useful. Whether youcreate the formatting objects on the fly or reuse them is up to you. is stored within the iostream in a more appropriate wayfor the CPU to understand. 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). C++11 got the two first. 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. 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.

> 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.

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. 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. When you unsynchronize the two, now you have to flush explicitly. ?

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.

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/.

I think the current design could be improved, but what's he's advocatedlooks to me like it'd do more harm than good. for security reasons, I want to get rid of type-unsafe printfphilosophy. - b) is a very strong issue! In general, streams have the advantage ofknowing the types at compile time, so can be faster. Output of above program when dummy file is redirected to stdin. Note that most modern compilers will check the arguments for you if theycan, i.e. where can I> find more info about that? 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++. Last update: 07.03.21. 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.

I would guess that (http://www.dietmar-kuehl.de/cxxrt/) is about that work but I haven't looked at it, I just googled it up now. I believe that the formatting isought to be bound to the object rather than the sink. Can anyone help me with the better solution O(n^3) for this Problem ? But its very important to use "\n" instead of endl for newline!!!

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. This does not seem like a good enough reason for a performance hit of 5x. I also don't really know if last thing i said is true. 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. supposed to mean? for example, format strings allows. 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. The most generic answer I couldgive is that it is implementation dependent, but I don't see any particularperformance bottleneck in either of them. [ See http://www.gotw.ca/resources/clcm.htm for info about ]. 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. Can you please explain what these two lines actually do. It turns out that iostream makes use of stdios buffering system. You might change the formatdynamically via: int foo(int i,int n) { const char * str1 "%x:%s\n"; const char * str2 "%d:%s\n"; if (i==0) { printf(str1,n,"hello"); else { printf(str2,n,"hello"); }}. Or do you have any other approach tosolve the problems in mind?

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. > 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. C++17 finally got the last one, but only with bug-attracting unsigned result type. 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. 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. 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. What is the line. 2.std::cout test: 1.154 s ; printf test: 0.230 s 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.

> Sometimes, I find code where the developers prefer to use printf/> fprintf, instead of ostream classes. The moment you do this, you have basically nothing more or less than amediocre imitation of the current iostreams architecture -- i.e. Side effects: sets std::ios_base::fixed, width 8, precision 4 on os. I always thought printf is faster than than cout. 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. Such problem is accompanied with Warning: large I/O data.

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 ran this on Windows after compiling with VC++ 2013 (both x86 and x64 versions). 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? "s (without using endl) takes about -

//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'"<

> - b) is a very strong issue! Perhaps you should look at the boostformatting library, which uses printf()-style format strings but hasbenefits. Can somebody plase explain that to me?

I've always heard the exact opposite, that printf is faster. I'm curious, how did you do your benchmarks? 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.

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). Therefore it isnt much useful to switch from one to another, just because its slow. Feel free to skip the initial Python and Java portions: https://ayandas.me/blog-tut/2019/04/06/speeding-up-iostreams-in-c++.html. Output from one run (with output redirected to a disk file) looked like this: As expected, results vary, but there are a few points I found interesting: I've recently edited the code to force a call to printf. GNU) allow reordering. The direct answer is that yes, that's okay. This makes the "current" formatting properties stored in the iostreamobject pretty useless. It has to parse a format string to know the size of and how to interpret its arguments. 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 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. If I remember correctly cout is almost always slower than printf due to some buffer synchronisation it does to ensure order of output.

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*. 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. Astream should know how to output character sequences and some kind of'sequence producer' only. > []Another issue for me is readability. 3450ms for printf(), 3420ms for cout. Writing code in comment? No. However using iostream with sync_with_stdio(false) makes i/o operations comparable to scanf/printf. >> - b) is a very strong issue!

Is CP useful to prepare students for academic research (in computer science, of course)? I do not see why c++ streams would be slower than cstreams: I/O are very slow operations per se. Really? here is an interesting record. Also see below.

It alsointimately bound to the streambuf (usually it outright owns it).

He managed to implement C++ streams very efficiently, though as I recall that was not a full implementation. An ideal output wouldgo along the lines. > so I have some questions lying around:> > - is printf really faster than streams in most of cases? Re convenience and re-ordering, only certain printf() implementations(e.g. It is obviously incorrect usage but it compiles andruns just fine. ].

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.

A detailed article on Fast Input Output in Competitive Programming, This article is contributed by Ayush Govil. I know that it's implementation dependent, but on my Linux box printf is 8x faster. You should benchmark it yourself.

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.

The problem is that this formatting class isgeneral rather than specific to the class being formatted. Nonsense. Effects: prints the virtual time t into os (in such and such format). 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. Thats also a library.

The operating system doesnt support printf. So the usage of locks makes the printf take longer time than the cout. -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated.