Is cin/cout slower than scanf/printf ?

There are few potential pitfalls with cin/cout :

  • By default, cin/cout waste time synchronizing themselves with the C library’s stdio buffers, so that you can freely intermix calls to scanf/printf with operations on cin/cout. Turn this off with std::ios_base::sync_with_stdio(false);
  • Many C++ tutorials tell you to write cout << endl instead of cout << '\n'. But endl is actually slower because it forces a flush, which is usually unnecessary. (You’d need to flush right before prompting the user for input from cin, but not when writing a million lines of output.) Write '\n' instead of endl.
  • There was a bug in very old versions of GCC (pre-2004) that significantly slowed down C++ iostreams. Don’t use ancient compilers.

Avoid these pitfalls, and cin/cout will be just as fast as scanf/printf. My benchmarks indicate that cin/cout is actually 5%–10% faster.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s