How much faster is C than C

Question

Or is it now the other way around   From what I ve heard there are some areas in which C  proves to be faster than C    but I ve never had the guts to test it by myself   Thought any of you could explain these differences in detail or point me to the right place for information on this

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There are some major differences between C# and C++ on the performance aspect:

C# is GC / heap based. The allocation and GC itself is overhead as the non locality of the memory access
C++ optimizer's have become very good over the years. JIT compilers cannot achieve the same level since they have only limited compilation time and don't see the global scope

Besides that programmer competence plays also a role. I have seen bad C++ code where classes where passed by value as argument all over the place. You can actually make the performance worse in C++ if you don't know what you are doing.

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Inspired by this  I did a quick test with 60 percent of common instruction needed in most of the programs   Here   s the C  code   for  int i 0  i lt 1000  i          StreamReader str   new StreamReader  file csv        StreamWriter stw   new StreamWriter  examp csv        string strL           while  strL   str ReadLine       null                ArrayList al   new ArrayList            string   strline   strL Split               al AddRange strline           foreach string str1 in strline                        stw Write str1                           stw Write   n              str Close        stw Close        String array and arraylist are used purposely to include those instructions   Here s the c   code   for  int i   0  i lt 1000  i          std  fstream file  file csv   ios  in       if   file is open                  std  cout  lt  lt   File not found  n           return 1             ofstream myfile      myfile open   example txt        std  string csvLine       while  std  getline file  csvLine                 std  istringstream csvStream csvLine           std  vector csvColumn          std  string csvElement           while  std  getline csvStream  csvElement                                   csvColumn push back csvElement                      for  std  vector  iterator j   csvColumn begin    j    csvColumn end      j                        myfile  lt  lt   j  lt  lt                           csvColumn clear            csvElement clear            csvLine clear            myfile  lt  lt    n             myfile close        file close        The input file size I used was 40 nbsp KB   And here s the result -   C   code ran in 9 seconds  C  code  4 seconds      Oh  but this was on Linux    With C  running on Mono    And C   with g     OK  this is what I got on Windows     Visual nbsp Studio nbsp 2003    C  code ran in 9 seconds  C   code     horrible 370 seconds

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There is no strict reason why a bytecode based language like C  or Java that has a JIT cannot be as fast as C   code  However C   code used to be significantly faster for a long time  and also today still is in many cases  This is mainly due to the more advanced JIT optimizations being complicated to implement  and the really cool ones are only arriving just now   So C   is faster  in many cases  But this is only part of the answer  The cases where C   is actually faster  are highly optimized programs  where expert programmers thoroughly optimized the hell out of the code  This is not only very time consuming  and thus expensive   but also commonly leads to errors due to over-optimizations   On the other hand  code in interpreted languages gets faster in later versions of the runtime   NET CLR or Java VM   without you doing anything  And there are a lot of useful optimizations JIT compilers can do that are simply impossible in languages with pointers  Also  some argue that garbage collection should generally be as fast or faster as manual memory management  and in many cases it is  You can generally implement and achieve all of this in C   or C  but it s going to be much more complicated and error prone   As Donald Knuth said   premature optimization is the root of all evil   If you really know for sure that your application will mostly consist of very performance critical arithmetic  and that it will be the bottleneck  and it s certainly going to be faster in C    and you re sure that C   won t conflict with your other requirements  go for C    In any other case  concentrate on first implementing your application correctly in whatever language suits you best  then find performance bottlenecks if it runs too slow  and then think about how to optimize the code  In the worst case  you might need to call out to C code through a foreign function interface  so you ll still have the ability to write critical parts in lower level language   Keep in mind that it s relatively easy to optimize a correct program  but much harder to correct an optimized program   Giving actual percentages of speed advantages is impossible  it largely depends on your code  In many cases  the programming language implementation isn t even the bottleneck  Take the benchmarks at http   benchmarksgame alioth debian org  with a great deal of scepticism  as these largely test arithmetic code  which is most likely not similar to your code at all

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We have had to determine if C  was comparable to C   in performance and I wrote some test programs for that  using Visual Studio 2005 for both languages   It turned out that without garbage collection and only considering the language  not the framework  C  has basically the same performance as C    Memory allocation is way faster in C  than in C   and C  has a slight edge in determinism when data sizes are increased beyond cache line boundaries  However  all of this had eventually to be paid for and there is a huge cost in the form of non-deterministic performance hits for C  due to garbage collection

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I know it isn t what you were asking  but C  is often quicker to write than C    which is a big bonus in a commercial setting

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Applications that require intensive memory access eg  image manipulation are usually better off written in unmanaged environment  C    than managed  C    Optimized inner loops with pointer arithmetics are much easier to have control of in C    In C  you might need to resort to unsafe code to even get near the same performance

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We have had to determine if C  was comparable to C   in performance and I wrote some test programs for that  using Visual Studio 2005 for both languages   It turned out that without garbage collection and only considering the language  not the framework  C  has basically the same performance as C    Memory allocation is way faster in C  than in C   and C  has a slight edge in determinism when data sizes are increased beyond cache line boundaries  However  all of this had eventually to be paid for and there is a huge cost in the form of non-deterministic performance hits for C  due to garbage collection

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I found this April 2020 read  https   www quora com Why-is-C-so-slow-compared-to-Python by a real-world programmer with 15  years of Software Development experience  It states that C  is slower usually because it is compiled to Common Intermediate Language  CIL  instead of machine code like C    The CIL is then put through Common Language Runtime  CLR  which outputs machine code  However  if you keep executing C  it will take the output of the machine code and cache it so the machine code is saved for the next execution  All in all  C  can be faster if you execute multiple times since it is in machine code after multiple executions  There is also comments that a good C   programmer can do optimizations that can be time consuming that will in end be optimized

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For  embarassingly parallel  problems  when using Intel TBB and OpenMP on C   I have observed a roughly 10x performance increase compared to similar  pure math  problems done with C  and TPL  SIMD is one area where C  cannot compete  but I also got the impression that TPL has a sizeable overhead   That said  I only use C   for performance-critical tasks where I know I will be able to multithread and get results quickly  For everything else  C   and occasionally F   is just fine

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C  may not be faster  but it makes YOU ME faster  That s the most important measure for what I do

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I would put it this way  programmers who write faster code  are the ones who are the more informed of what makes current machines go fast  and incidentally they are also the ones who use an appropriate tool that allows for precise low-level and deterministic optimisation techniques  For these reasons  these people are the ones who use C C   rather than C   I would go as far as stating this as a fact

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The garbage collection is the main reason Java  CANNOT be used for real-time systems    When will the GC happen  How long will it take    This is non-deterministic

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After all  the answers have to be somewhere  haven t they      Umm  no   As several replies noted  the question is under-specified in ways that invite questions in response  not answers  To take just one way    the question conflates language with language implementation - this C program is both 2 194 times slower and 1 17 times faster than this C  program - we would have to ask you  Which language implementations    And then which programs  Which machine  Which OS  Which data set

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In my experience  and I have worked a lot with both languages   the main problem with C  compared to C   is high memory consumption  and I have not found a good way to control it  It was the memory consumption that would eventually slow down  NET software   Another factor is that JIT compiler cannot afford too much time to do advanced optimizations  because it runs at runtime  and the end user would notice it if it takes too much time  On the other hand  a C   compiler has all the time it needs to do optimizations at compile time  This factor is much less significant than memory consumption  IMHO

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From what I ve heard      Your difficulty seems to be in deciding whether what you have heard is credible  and that difficulty will just be repeated when you try to assess the replies on this site   How are you going to decide if the things people say here are more or less credible than what you originally heard   One way would be to ask for evidence   When someone claims  there are some areas in which C  proves to be faster than C    ask them why they say that  ask them to show you measurements  ask them to show you programs  Sometimes they will simply have made a mistake  Sometimes you ll find out that they are just expressing an opinion rather than sharing something that they can show to be true   Often information and opinion will be mixed up in what people claim  and you ll have to try and sort out which is which  For example  from the replies in this forum     Take the benchmarks at http   shootout alioth debian org  with a great deal of scepticism  as these largely test arithmetic code  which is most likely not similar to your code at all    Ask yourself if you really understand what  these largely test arithmetic code  means  and then ask yourself if the author has actually shown you that his claim is true   That s a rather useless test  since it really depends on how well the individual programs have been optimized  I ve managed to speed up some of them by 4-6 times or more  making it clear that the comparison between unoptimized programs is rather silly    Ask yourself whether the author has actually shown you that he s managed to  speed up some of them by 4-6 times or more  - it s an easy claim to make

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I ve tested vector in C   and C  equivalent - List and simple 2d arrays   I m using Visual C  C   2010 Express editions  Both projects are simple console applications  I ve tested them in standard  no custom settings  release and debug mode  C  lists run faster on my pc  array initialization is also faster in C   math operations are slower   I m using Intel Core2Duo P8600 2 4GHz  C  -  NET 4 0   I know that vector implementation is different than C  list  but I just wanted to test collections that I would use to store my objects  and being able to use index accessor    Of course you need to clear memory  let s say for every use of new   but I wanted to keep the code simple   C   vector test   static void TestVector         clock t start finish      start clock        vector lt vector lt double gt  gt  myList vector lt vector lt double gt  gt         int i 0      for  i 0  i lt 500  i                  myList push back vector lt double gt              for int j 0 j lt 50000 j                myList i  push back j i             finish clock        cout lt  lt  finish-start  lt  lt endl      cout lt  lt  double finish - start  CLOCKS PER SEC       C  list test   private static void TestVector          DateTime t1   System DateTime Now      List lt List lt double gt  gt  myList   new List lt List lt double gt  gt         int i   0      for  i   0  i  lt  500  i                  myList Add new List lt double gt              for  int j   0  j  lt  50000  j                myList i  Add j  i             DateTime t2   System DateTime Now      Console WriteLine t2 - t1       C   - array   static void TestArray         cout  lt  lt   Normal array test    lt  lt  endl      const int rows   5000      const int columns   9000      clock t start  finish       start   clock        double   arr   new double  rows       for  int i   0  i  lt  rows  i            arr i    new double columns       finish   clock         cout  lt  lt   finish - start   lt  lt  endl       start   clock        for  int i   0  i  lt  rows  i            for  int j   0  j  lt  columns  j                arr i  j    i   j      finish   clock         cout  lt  lt   finish - start   lt  lt  endl      C  - array   private static void TestArray         const int rows   5000      const int columns   9000      DateTime t1   System DateTime Now      double     arr   new double rows         for  int i   0  i  lt  rows  i            arr i    new double columns       DateTime t2   System DateTime Now       Console WriteLine t2 - t1        t1   System DateTime Now      for  int i   0  i  lt  rows  i            for  int j   0  j  lt  columns  j                arr i  j    i   j      t2   System DateTime Now       Console WriteLine t2 - t1        Time   Release Debug   C     600   606 ms array init  200   270 ms array fill  1sec  13sec  vector init  amp  fill     Yes  13 seconds  I always have problems with lists vectors in debug mode    C     20    20  ms array init  403   440 ms array fill  710   742 ms list init  amp  fill

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I m going to start by disagreeing with part of the accepted  and well-upvoted  answer to this question by stating   There are actually plenty of reasons why JITted code will run slower than a properly optimized C    or other language without runtime overhead   program including    compute cycles spent on JITting code at runtime are by definition unavailable for use in program execution  any hot paths in the JITter will be competing with your code for instruction and data cache in the CPU   We know that cache dominates when it comes to performance and native languages like C   do not have this type of contention  by definition  a run-time optimizer s time budget is necessarily much more constrained than that of a compile-time optimizer s  as another commenter pointed out    Bottom line  Ultimately  you will almost certainly be able to create a faster implementation in C   than you could in C    Now  with that said  how much faster really isn t quantifiable  as there are too many variables  the task  problem domain  hardware  quality of implementations  and many other factors   You ll have run tests on your scenario to determine the the difference in performance  and then decide whether it is worth the the additional effort and complexity   This is a very long and complex topic  but I feel it s worth mentioning for the sake of completeness that C  s runtime optimizer is excellent  and is able to perform certain dynamic optimizations at runtime that are simply not available to C   with its compile-time  static  optimizer   Even with this  the advantage is still typically deeply in the native application s court  but the dynamic optimizer is the reason for the  almost certainly  qualifier given above    --  In terms of relative performance  I was also disturbed by the figures and discussions I saw in some other answers  so I thought I d chime in and at the same time  provide some support for the statements I ve made above   A huge part of the problem with those benchmarks is you can t write C   code as if you were writing C  and expect to get representative results  eg  performing thousands of memory allocations in C   is going to give you terrible numbers    Instead  I wrote slightly more idiomatic C   code and compared against the C  code  Wiory provided   The two major changes I made to the C   code were   1  used vector  reserve    2  flattened the 2d array to 1d to achieve better cache locality  contiguous block   C    NET 4 6 1   private static void TestArray         const int rows   5000      const int columns   9000      DateTime t1   System DateTime Now      double     arr   new double rows         for  int i   0  i  lt  rows  i            arr i    new double columns       DateTime t2   System DateTime Now       Console WriteLine t2 - t1        t1   System DateTime Now      for  int i   0  i  lt  rows  i            for  int j   0  j  lt  columns  j                arr i  j    i      t2   System DateTime Now       Console WriteLine t2 - t1       Run time  Release   Init  124ms  Fill  165ms   C  14  Clang v3 8 C2    include  lt iostream gt   include  lt vector gt   auto TestSuite  ColMajorArray         constexpr size t ROWS   5000      constexpr size t COLS   9000       auto initStart   std  chrono  steady clock  now         auto arr   std  vector lt double gt         arr reserve ROWS   COLS        auto initFinish   std  chrono  steady clock  now        auto initTime   std  chrono  duration cast lt std  chrono  microseconds gt  initFinish - initStart        auto fillStart   std  chrono  steady clock  now         for auto i   0  r   0  r  lt  ROWS    r                for  auto c   0  c  lt  COLS    c                        arr i      static cast lt double gt  r   c                        auto fillFinish   std  chrono  steady clock  now        auto fillTime   std  chrono  duration cast lt std  chrono  milliseconds gt  fillFinish - fillStart        return std  make pair initTime  fillTime       Run time  Release   Init  398  s  yes  that s microseconds   Fill  152ms  Total Run times   C   289ms  C   152ms  roughly 90  faster   Observations   Changing the C  implementation to the same 1d array implementation yielded Init  40ms  Fill  171ms  Total  211ms  C   was still almost 40  faster   It is much harder to design and write  fast  code in C   than it is to write  regular  code in either language  It s  perhaps  astonishingly easy to get poor performance in C    we saw that with unreserved vectors performance   And there are lots of pitfalls like this  C  s performance is rather amazing when you consider all that is going on at runtime   And that performance is comparatively easy to access  More anecdotal data comparing the performance of C   and C   https   benchmarksgame alioth debian org u64q compare php lang gpp amp lang2 csharpcore   The bottom line is that C   gives you much more control over performance   Do you want to use a pointer   A reference   Stack memory   Heap   Dynamic polymorphism or eliminate the runtime overhead of a vtable with static polymorphism  via templates CRTP    In C   you have to    er  get to make all these choices  and more  yourself  ideally so that your solution best addresses the problem you re tackling   Ask yourself if you actually want or need that control  because even for the trivial example above  you can see that although there is a significant improvement in performance  it requires a deeper investment to access

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It really depends on what you re trying to accomplish in your code   I ve heard that it s just stuff of urban legend that there is any performance difference between VB NET  C  and managed C     However  I ve found  at least in string comparisons  that managed C   beats the pants off of C   which in turn beats the pants off of VB NET   I ve by no means done any exhaustive comparisons in algorithmic complexity between the languages   I m also just using the default settings in each of the languages   In VB NET I m using settings to require declaration of variables  etc   Here is the code I m using for managed C     As you can see  this code is quite simple    I m running the same in the other languages in Visual Studio 2013 with  NET 4 6 2    include  stdafx h   using namespace System  using namespace System  Diagnostics   bool EqualMe String  first  String  second        return first- gt Equals second     int main array lt String   gt   args        Stopwatch  sw   gcnew Stopwatch        sw- gt Start        for  int i   0  i  lt  100000  i                  EqualMe L one   L two              sw- gt Stop        Console  WriteLine sw- gt ElapsedTicks       return 0

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NET languages can be as fast as C   code  or even faster  but C   code will have a more constant throughput as the  NET runtime has to pause for GC  even if it s very clever about its pauses   So if you have some code that has to consistently run fast without any pause   NET will introduce latency at some point  even if you are very careful with the runtime GC

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The garbage collection is the main reason Java  CANNOT be used for real-time systems    When will the GC happen  How long will it take    This is non-deterministic

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If I m not mistaken  C  templates are determined at runtime  This must be slower than compile time templates of C      And when you take in all the other compile-time optimizations mentioned by so many others  as well as the lack of safety that does  indeed  mean more speed     I d say C   is the obvious choice in terms of raw speed and minimum memory consumption  But this also translates into more time developing the code and ensuring you aren t leaking memory or causing any null pointer exceptions   Verdict    C   Faster development  slower run C    Slow development  faster run

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It s an extremely vague question without real definitive answers   For example  I d rather play 3D-games that are created in C   than in C   because the performance is certainly a lot better   And I know XNA  etc   but it comes no way near the real thing    On the other hand  as previously mentioned  you should develop in a language that lets you do what you want quickly  and then if necessary optimize

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One particular scenario where C   still has the upper hand  and will  for years to come  occurs when polymorphic decisions can be predetermined at compile time   Generally  encapsulation and deferred decision-making is a good thing because it makes the code more dynamic  easier to adapt to changing requirements and easier to use as a framework  This is why object oriented programming in C  is very productive and it can be generalized under the term    generalization     Unfortunately  this particular kind of generalization comes at a cost at run-time   Usually  this cost is non-substantial but there are applications where the overhead of virtual method calls and object creation can make a difference  especially since virtual methods prevent other optimizations such as method call inlining   This is where C   has a huge advantage because you can use templates to achieve a different kind of generalization which has no impact on runtime but isn t necessarily any less polymorphic than OOP  In fact  all of the mechanisms that constitute OOP can be modelled using only template techniques and compile-time resolution   In such cases  and admittedly  they re often restricted to special problem domains   C   wins against C  and comparable languages

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Well  it depends  If the byte-code is translated into machine-code  and not just JIT   I mean if you execute the program  and if your program uses many allocations deallocations it could be faster because the GC algorithm just need one pass  theoretically  through the whole memory once  but normal malloc realloc free C C   calls causes an overhead on every call  call-overhead  data-structure overhead  cache misses        So it is theoretically possible  also for other GC languages    I don t really see the extreme disadvantage of not to be able to use metaprogramming with C  for the most applications  because the most programmers don t use it anyway   Another big advantage is that the SQL  like the LINQ  extension   provides opportunities for the compiler to optimize calls to databases  in other words  the compiler could compile the whole LINQ to one  blob  binary where the called functions are inlined or for your use optimized  but I m speculating here

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I suppose there are applications written in C  running fast  as well as there are more C   written apps running fast  well C   just older    and take UNIX too     - the question indeed is - what is that thing  users and developers are complaining about     Well  IMHO  in case of C  we have very comfort UI  very nice hierarchy of libraries  and whole interface system of CLI  In case of C   we have templates  ATL  COM  MFC and whole shebang of alreadyc written and running code like OpenGL  DirectX and so on    Developers complains of indeterminably risen GC calls in case of C   means program runs fast  and in one second - bang  it s stuck   To write code in C  very simple and fast  not to forget that also increase chance of errors   In case of C     developers complains of memory leaks  - means crushes  calls between DLLs  as well as of  DLL hell  - problem with support and replacement libraries by newer ones    I think more skill you ll have in the programming language  the more quality  and speed  will characterize your software

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C C   can perform vastly better in programs where there are either large arrays or heavy looping iteration over arrays  of any size   This is the reason that graphics are generally much faster in C C    because heavy array operations underlie almost all graphics operations   NET is notoriously slow in array indexing operations due to all the safety checks  and this is especially true for multi-dimensional arrays  and  yes  rectangular C  arrays are even slower than jagged C  arrays    The bonuses of C C   are most pronounced if you stick directly with pointers and avoid Boost  std  vector and other high-level containers  as well as inline every small function possible  Use old-school arrays whenever possible  Yes  you will need more lines of code to accomplish the same thing you did in Java or C  as you avoid high-level containers  If you need a dynamically sized array  you will just need to remember to pair your new T   with a corresponding delete   statement  or use std  unique ptr  mdash the price for the extra speed is that you must code more carefully  But in exchange  you get to rid yourself of the overhead of managed memory   garbage collector  which can easily be 20  or more of the execution time of heavily object-oriented programs in both Java and  NET  as well as those massive managed memory array indexing costs  C   apps can also benefit from some nifty compiler switches in certain specific cases   I am an expert programmer in C  C    Java  and C   I recently had the rare occasion to implement the exact same algorithmic program in the latter 3 languages  The program had a lot of math and multi-dimensional array operations  I heavily optimized this in all 3 languages  The results were typical of what I normally see in less rigorous comparisons  Java was about 1 3x faster than C   most JVMs are more optimized than the CLR   and the C   raw pointer version came in about 2 1x faster than C   Note that the C  program only used safe code mdash it is my opinion that you might as well code it in C   before using the unsafe keyword   Lest anyone think I have something against C   I will close by saying that C  is probably my favorite language  It is the most logical  intuitive and rapid development language I ve encountered so far  I do all my prototyping in C   The C  language has many small  subtle advantages over Java  yes  I know Microsoft had the chance to fix many of Java s shortcomings by entering the game late and arguably copying Java   Toast to Java s Calendar class anyone  If Microsoft ever spends real effort to optimize the CLR and the  NET JITter  C  could seriously take over  I m honestly surprised they haven t already mdash they did so many things right in the C  language  why not follow it up with heavy-hitting compiler optimizations  Maybe if we all beg

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C    or C for that matter  gives you fine-grained control over your data structures  If you want to bit-twiddle you have that option  Large managed Java or  NET apps  OWB  Visual nbsp Studio nbsp 2005  that use the internal data structures of the Java  NET libraries carry the baggage with them  I ve seen OWB designer sessions using over 400 nbsp MB of RAM and BIDS for cube or ETL design getting into the 100 s of MB as well   On a predictable workload  such as most benchmarks that repeat a process many times  a JIT can get you code that is optimised well enough that there is no practical difference   IMO on large applications the difference is not so much the JIT as the data structures that the code itself is using  Where an application is memory-heavy you will get less efficient cache usage  Cache misses on modern CPUs are quite expensive  Where C or C   really win is where you can optimise your usage of data structures to play nicely with the CPU cache

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It s five oranges faster  Or rather  there can be no  correct  blanket answer  C   is a statically compiled language  but then  there s profile guided optimization  too   C  runs aided by a JIT compiler  There are so many differences that questions like    how much faster    cannot be answered  not even by giving orders of magnitude

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In theory  for long running server-type application  a JIT-compiled language can become much faster than a natively compiled counterpart   Since the JIT compiled language is generally first compiled to a fairly low-level intermediate language  you can do a lot of the high-level optimizations right at compile time anyway   The big advantage comes in that the JIT can continue to recompile sections of code on the fly as it gets more and more data on how the application is being used   It can arrange the most common code-paths to allow branch prediction to succeed as often as possible   It can re-arrange separate code blocks that are often called together to keep them both in the cache   It can spend more effort optimizing inner loops   I doubt that this is done by  NET or any of the JREs  but it was being researched back when I was in university  so it s not unreasonable to think that these sort of things may find their way into the real world at some point soon

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As usual  it depends on the application   There are cases where C  is probably negligibly slower  and other cases where C   is 5 or 10 times faster  especially in cases where operations can be easily SIMD d

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Applications that require intensive memory access eg  image manipulation are usually better off written in unmanaged environment  C    than managed  C    Optimized inner loops with pointer arithmetics are much easier to have control of in C    In C  you might need to resort to unsafe code to even get near the same performance

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For graphics the standard C  Graphics class is way slower than GDI accessed via C C    I know this has nothing to do with the language per se  more with the total  NET platform  but Graphics is what is offered to the developer as a GDI replacement  and its performance is so bad I wouldn t even dare to do graphics with it   We have a simple benchmark we use to see how fast a graphics library is  and that is simply drawing random lines in a window  C   GDI is still snappy with 10000 lines while C  Graphics has difficulty doing 1000 in real-time

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