[C++]Template Argument Deduction: automatic type conversation is not allowed

  
    

   
      1 
   
     #include 
   
     <
   
     string
   
     >
   
     

   
      2 
   
     
   
     using
   
      
   
     namespace
   
      std;

   
      3 
   
     template 
   
     <
   
     typename T
   
     >
   
     

   
      4 
   
     inline T Add(
   
     const
   
      T
   
     &
   
      a,
   
     const
   
      T
   
     &
   
      b){

   
      5 
   
      
   
     return
   
      a
   
     +
   
     b;

   
      6 
   
     }

   
      7 
   
     

   
      8 
   
     
   
     string
   
      Add2(
   
     const
   
      
   
     string
   
     &
   
      a, 
   
     const
   
      
   
     string
   
     &
   
      b)

   
      9 
   
     {

   
     10 
   
      
   
     return
   
      a
   
     +
   
     b;

   
     11 
   
     }

   
     12 
   
     
   
     int
   
      _tmain(
   
     int
   
      argc, _TCHAR
   
     *
   
      argv[])

   
     13 
   
     {

   
     14 
   
      
   
     string
   
      a(
   
     "
   
     test
   
     "
   
     );

   
     15 
   
      
   
     //
   
     Add(a,"b"); 
   
     //
   
     error: template parameter 'T' is ambiguous
   
     

   
     16 
   
     
   
      Add2(a,
   
     "
   
     b
   
     "
   
     ); 
   
     //
   
     OK for none template parameter

   
     17 
   
     

   
     18 
   
      
   
     //
   
     how to fix it.
   
     

   
     19 
   
     
   
      Add(a,
   
     string
   
     (
   
     "
   
     b
   
     "
   
     ));

   
     20 
   
      Add(a,static_cast
   
     <
   
     string
   
     >
   
     (
   
     "
   
     b
   
     "
   
     ));

   
     21 
   
      Add
   
     <
   
     string
   
     >
   
     (a,
   
     "
   
     b
   
     "
   
     );

   
     22 
   
     

   
     23 
   
      
   
     return
   
      
   
     0
   
     ;

   
     24 
   
     }