What is the definition of a string type for a few bytes??

Test code:

#include <iostream>
using namespace Std;
int main (void)
{
String name;
cout<< "sizeof (name)" <<sizeof (name) <<endl;

return 0;
}

The same code runs on different platforms:

First run on QT using MINGW with the output sizeof (name) = 4; (as a pointer ...)

Run on QT using MSVC2010 to output sizeof (name) = 28;

Then the VS2010 on the output sizeof (name) = 32;

Finally, VS2013 on the output sizeof (name) = 28;

Do not understand the ~ ~??

What is the definition of a string type for a few bytes??