Most useful or amazing STL short liners

Question

I\'m looking for practical and educational samples of C++ / STL code fitting in few lines. My actual favorites are:

1. Empty a vector freeing its reserved memory:<

Answer 1

I like this one for looping over each line in a file. From a Andrew Koenig column in Dr. Dobbs.

for (string s; getline(stream,s); ) {
  // Process line
}