6 ms·

Linus is probably the %1 of people in the world who actually needs to get the performance gain that C has over C++ - as for the rest of us? Probably doesn't ma

Linus is probably the %1 of people in the world who actually needs to get the performance gain that C has over C++ - as for the rest of us? Probably doesn't matter.

Game_Ender 15y ago
> needs to get the performance gain that C has over C++ With RTTI and Exceptions disabled you should be able to get almost identical performance with C and C++. In some cases C++ compiler has additional information that can allow it to produce faster code as well.
- cube13 15y ago
  You also need to not use: STL(most implementations are too slow) Boost or STLPort(namespace and compatability issues if you're not producing executables) Most OO features like inheritance and polymorphism(a lot of that is resolved at runtime, which eats cycles) Function overloading(debatable, since the compiler should resolve the function signatures at compile time) You're pretty much left with C with namespaces at that point.
  - jmccaffrey 15y ago
    C++ actually has some performance advantages over C, especially relating to static polymorphism (qsort v. std::sort)
    - aidenn0 15y ago
      Technically you can do tricks like that with the C preprocessor, though it is a bit ugly and lacks automatic instantiation.
      - yannickt 15y ago
        It is also not type safe.
- sarvesh 15y ago
  Without RTTI how would you make it portable? From the thread it is clear he was also concerned about portability.
- dedward 15y ago
  Yup, and if you avoid using any of the new language constructs like objects and whatnot that C++ brings and basically stick to standard C, maybe using just a bit of C++ sugar here and htere, true.... but at that point you might as well be using C, and the argument is really moot.
  - Game_Ender 15y ago
    You are wrong. Those the only two features that incur any performance penalty for just existing, and even then it's implementation dependent and in some cases can be zero (ie. zero cost exceptions). Other things that are possibly slow, like virtual functions, can be avoided in specific cases when needed. This is similar to many how C projects use structures of functions pointers, for abstraction, but not everywhere (including the Linux kernel).
    - deleted 15y ago
      [deleted]
cageface 15y ago
C++ can actually be faster because it doesn't throw away as much type information. A good, typed C++ quicksort implementation, for example, will be faster than a C version using void*.
- cygx 15y ago
  One of the reasons for the performance difference is that you can't inline into the libc DLL blob: If you use qsort(), you'll get a lot of overhead from calling the comparison function. If you use a custom quicksort implementation and put it into the same translation unit as the comparison function (or compile statically and use link-time optimizations with a sufficiently advanced compiler) you can get the same performance out of C.
  - cageface 15y ago
    Function call overhead is only one of the issues with the C version based on void pointers. Check out Stroustrup's keynote at Going Native 2012 for more details: http://channel9.msdn.com/Events/GoingNative/GoingNative-2012/Keynote-Bjarne-Stroustrup-Cpp11-Style http://channel9.msdn.com/Events/GoingNative/GoingNative-2012...

Linus is probably the %1 of people in the world who actually needs to get the performance gain that C has over C++ - as for the rest of us? Probably doesn't matter.

Game_Ender 15y ago

> needs to get the performance gain that C has over C++ With RTTI and Exceptions disabled you should be able to get almost identical performance with C and C++. In some cases C++ compiler has additional information that can allow it to produce faster code as well.

cube13 15y ago
You also need to not use: STL(most implementations are too slow) Boost or STLPort(namespace and compatability issues if you're not producing executables) Most OO features like inheritance and polymorphism(a lot of that is resolved at runtime, which eats cycles) Function overloading(debatable, since the compiler should resolve the function signatures at compile time) You're pretty much left with C with namespaces at that point.
- jmccaffrey 15y ago
  C++ actually has some performance advantages over C, especially relating to static polymorphism (qsort v. std::sort)
  - aidenn0 15y ago
    Technically you can do tricks like that with the C preprocessor, though it is a bit ugly and lacks automatic instantiation.
    - yannickt 15y ago
      It is also not type safe.
sarvesh 15y ago
Without RTTI how would you make it portable? From the thread it is clear he was also concerned about portability.
dedward 15y ago
Yup, and if you avoid using any of the new language constructs like objects and whatnot that C++ brings and basically stick to standard C, maybe using just a bit of C++ sugar here and htere, true.... but at that point you might as well be using C, and the argument is really moot.
- Game_Ender 15y ago
  You are wrong. Those the only two features that incur any performance penalty for just existing, and even then it's implementation dependent and in some cases can be zero (ie. zero cost exceptions). Other things that are possibly slow, like virtual functions, can be avoided in specific cases when needed. This is similar to many how C projects use structures of functions pointers, for abstraction, but not everywhere (including the Linux kernel).
  - deleted 15y ago
    [deleted]

cageface 15y ago

C++ can actually be faster because it doesn't throw away as much type information. A good, typed C++ quicksort implementation, for example, will be faster than a C version using void*.

cygx 15y ago
One of the reasons for the performance difference is that you can't inline into the libc DLL blob: If you use qsort(), you'll get a lot of overhead from calling the comparison function. If you use a custom quicksort implementation and put it into the same translation unit as the comparison function (or compile statically and use link-time optimizations with a sufficiently advanced compiler) you can get the same performance out of C.
- cageface 15y ago
  Function call overhead is only one of the issues with the C version based on void pointers. Check out Stroustrup's keynote at Going Native 2012 for more details: http://channel9.msdn.com/Events/GoingNative/GoingNative-2012/Keynote-Bjarne-Stroustrup-Cpp11-Style http://channel9.msdn.com/Events/GoingNative/GoingNative-2012...