title: Guaranteed precision of sqrt function in C/C++
body: <p>Everyone knows <code>sqrt</code> function from <code>math.h</code>/<code>cmath</code> in C/C++ - it returns square root of its argument. Of course, it has to do it with some error, because not every number can be stored precisely. But am I guaranteed that the result has some precision? For example, 'it's the best approximation of square root that can be represented in the floating point type used<code>or</code>if you calculate square of the result, it will be as close to initial argument as possible using the floating point type given`?</p>
  
  <p>Does C/C++ standard have something about it?</p>