Re: C++ is Slow?

nw wrote:


  My own practical experience has shown that for example if you are
reading&parsing tons of formatted data (in ascii format) and/or
outputting tons of formatted data (in ascii), switching from C++ streams
to C streams can produce a very considerable speedup (it can be at least
twice as fast) with all compilers I have tried. I have been in several
such projects where parsing of large ascii input files were necessary,
and in each case, with different compilers, switching to C streams gave
a very large speedup.

  I haven't tested what happens if you simply read/write a large block
of binary data with fread()/fwrite() or the iostream equivalents, but I
assume that in this case the difference should be minimal, if there is any.


  While in theory iostream could be even faster than C streams for
certain operations (eg. printf() vs. std::cout) because in the latter
typing can be performed at compile time while in the former it's done at
runtime (by parsing the format string), in practice most iostream
implementations are considerably slower than the C equivalents. One
reason for this might be that most iostream operations are performed by
virtual functions, which probably cannot be inlined, or other such
reasons. Another reason may be that compiler makers simply haven't
optimized iostream as well as the C stream functions have been.