Weird unused static string declaration in C++ code

Question

Today in a popular problem solving site, i submitted a solution for a problem, then looked up a more faster code to find out what is the reason that his/her code is running

Answer 1

You have guessed most of it:

• it is executed before the main by initializing a static variable using a lambda
• it disables i/o related things that will slow down execution:
  • std::ios::sync_with_stdio
  • cin.tie(nullptr) will untie cin from cout. See below
• initializing a string like this is not costly because it won't cause a heap allocation for an empty string

from cplusplus.com:

The tied stream is an output stream object which is flushed before each i/o operation in this stream object

I guess this problem takes input from cin and you provide the answer on cout, from this point onward, writing to cout will be faster.