字符串处理1

string的妙用：

#include <iostream>
#include <string>
using namespace std;

int main()
{
   string filename, basename, extname, tmpname;
   const string suffix("tmp");
   cin >> filename ;
   size_t index = filename.find(".");
   if (index == string::npos)
   {
       filename += "." + suffix;
   } 
   else
   {
       basename = filename.substr(0,index+1);
       extname = filename.substr(index+1);
       if (extname.empty())
       {
           filename += suffix;
       } 
       else
       {
          if (extname == "dat")
          {
              filename = basename + suffix;
          }
          if (extname == "tmp")
          {
              filename = basename + "xxx";
          }
       }
   }
   cout << filename << endl;
}