Not to mention that often compiles 10~15 times slower than and has twice the binary overhead std:cout won't actually call printf. Not really. I am aware of this. where can I> find more info about that? > - b) is a very strong issue! (Anything coming in C++0x? I am still reading and evaluating your responses (very quick for amoderated group. Side effects: sets std::ios_base::fixed, width 8, precision 4 on os. So, cin wastes time synchronizing itself with the underlying C-librarys stdio buffer, so that calls to bothscanf()and cin can be interleaved. 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Differentiate printable and control character in C ? Recent changes: Fixed OP usages of tokens readme, I wrote an entire blog post about this. However: 1. 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. 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. http://codeforces.com/contest/436/submission/6890501, http://codeforces.com/contest/436/submission/6890486, I don't know for sure but maybe you have TLE on the first submission because of combining cin and printf? supposed to mean? >> - b) is a very strong issue! is there a good workaround with>> streams?> > Hmm -- I'm not sure if I understand that point. 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). Do you have any sources for your claim? The good thing is that libstdc++ provides an option to turn off synchronization of all the iostream standard streams with their corresponding standard C streams using. Printf is faster. is there a good workaround withstreams? An output stream should be something that knows only to outputsequences of characters. However C++ streams have the technical potential to be faster. It will make no difference mostly, but you could consider using '\n' instead of std::endl. generate link and share the link here. I've always heard the exact opposite, that printf is faster. 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"); }}. for example, format strings allows. Which is probablythe wrong place to do this kind of stuff. What do you think?>. 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. for security reasons, I want to get rid of type-unsafe printfphilosophy. > 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. 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. 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. As you can see, using printf and then fflushing takes about 5 times less time than using std::cout. 90ms for printf(), 79ms for cout. Dietmar Kuehl did some work on that in the C++03 days. Can anyone help me with the better solution O(n^3) for this Problem ? 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. "s (without using endl) takes about - Whereas,you can easily write a operator<< for your user-defined type.
In general, streams have the advantage ofknowing the types at compile time, so can be faster. 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. > An output stream should be something that knows only to output> sequences of characters. What do you think?
Effects: sets std::ios_base::fixed, width 8, precision 4 on os, and prints the virtual time t into os. Whether youcreate the formatting objects on the fly or reuse them is up to you. It depends on which operating system u are using, but actually it doesnt make much difference. That may not the greatest frustration, but a greatannoyance that you encounter often, here and there. printf is also Turing Complete, FYI. But i saw printf and ither printf-like functions defined in linux kernel. 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. It is obviously incorrect usage but it compiles andruns just fine. Is CP useful to prepare students for academic research (in computer science, of course)? 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. I think the current design could be improved, but what's he's advocatedlooks to me like it'd do more harm than good. 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? 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. 5.std::cout test: 1.108 s ; printf test: 0.232 s I saw some people claim cout is faster than printf in some cases and i wondered if it's true. It's notvery hard to write one, and I also have done that. I have an answer to this! 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). Therefore it isnt much useful to switch from one to another, just because its slow. 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. I decided to write a quick test program to get at least some idea of which techniques did what. One problem is that that one is using synced streams, which are already slower. getline() Function and Character Array in C++. Hello everybody i have a question for you. At least that was true for gcc back a few years when I was trying out competitive programming. Such an approach can be emulated today but inefficiently and withoutremoving the cost of all the unnecessary iostream cruft. 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. 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. Please have a look at these two solutions, the code using cout is accepted but the code using printf is giving TLE. 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. It doesn't need to know anything about *any*default formatting. Perhaps you should look at the boostformatting library, which uses printf()-style format strings but hasbenefits. You should benchmark it yourself. See James Kanze's formatting classes *Fmtand StateSavingManip at ,for an example of approach (2). Of one of code The only performance penalty I see is that printf has to parse theformat string, while the current output format (setprecision, hex,dec etc.) by jetnet aa. It will call something more like fwrite. 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*. is stored within the iostream in a more appropriate wayfor the CPU to understand. No. 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. If the iostreams classes are intended to be the way they are now,that's too bad. In some Online Judge if we use cout , we get TLE but if we use printf we get Accepted. > A stream buffer knows only about reading/writing streams of characters. Due to the locks being used by printf, on a large scale, the printf takes more time when compared to cout. > - b) is a very strong issue! That's the reason such librariesuse placeholders like '%1''%5' in their format string insteadof '%d' '%s'. Can somebody plase explain that to me? In addition, doesn't the iostream library also incur the overhead ofa virtual function call for every character read or written? > >> This makes the "current" formatting properties stored in the iostream>> object pretty useless.> > Nonsense. Isn't all output streams converted to printf, because that's what operating systems support? > 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 alsointimately bound to the streambuf (usually it outright owns it). Do you really want to keep in mind that the state of os is changedafter you print a VirtualTime object into os? ), 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. Isincerely hope modern streams implementations have at least ripped offthe *printf() implementation to inline it, and hopefully optimised ita bit in the process. *lf", ) call toprepare the data, hence ensuring real numbers rendered slower. How to split a string in C/C++, Python and Java? > > Don't get me wrong: overall, I tend to view modality as a shortcoming,> and I prefer to avoid it in general. Streams aresimply not designed to be used this way. 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. You can not *reorder*> the arguments for printf matching values always have to appear in the> order given within the format string. I believe that the formatting isought to be bound to the object rather than the sink. here is an interesting record.
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. 