title: How to check conversion from C++ string to unsigned int
body: <p>I need to:</p>
  
  <p>1) Find what is the maximum unsigned int value on my current system. I didn't find it on limits.h. Is it safe to write <code>unsigned int maxUnsInt = 0 - 1;</code>? I also tried <code>unsigned int maxUnsInt = MAX_INT * 2 + 1</code> that returns the correct value but the compiler shows a warning about int overflow operation.</p>
  
  <p>2) Once found, check if a C++ string (that I know it is composed only by digits) exceeded the maximum unsigned int value on my system.</p>
  
  <p>My final objective is to convert the string to a unsigned int using atoi if and only if it is a valid unsigned int. I would prefer to use only the standard library.</p>