title: std::map default value for build-in type
body: <p>Recently, I was confused by the std::map operator[] function.
  In the MSDN library, it says: "If the argument key value is not found, then it is inserted along with the default value of the data type."
  I tryed to search much more exactly explanation for this issue. For example here:
  <a href="https://stackoverflow.com/questions/2333728/stdmap-default-value">std::map default value</a>
  In this page, Michael Anderson said that "the default value is constructed by the default constructor(zero parameter constructor)".</p>
  
  <p>Now my quest comes to this:"what the default value for the build-in type?". Was it compiler related? Or is there a standard for this issue by the c++ stardard committee?</p>
  
  <p>I did a test on visual studio 2008 for the "int" type, and found the "int" type is construted with the value 0.</p>