string - get length of `wchar_t*` in c++ -

Please, how can I type a variable type length in wchar_t * C ++ ?

Example of the code given below:

  wchar_t * dimObjPrefix = L "retro_";  

I need to find out how many letters are included in dimObjPrefix

  szaffe (wchar_t);   Edit:  
 
 I have just seen the  string  tag if you  Want to know the size of the  wchar_t  string  ( wchar_t * ), then you want to use it: 
 
  size_t wcslen (Const wchar_t * ws);