coversion

[dskp]

my problem is to get number of decimals digits after the decimal in a number of type double.So i have written below code.but it displays the ERROR which is


cannot convert parameter 1 from 'std::string' to 'char *'

string s;
 string t;
 wsprintf(s, "%g" ,error_bound);
 t = s.substr(s.find(".")+1);

 return t.length();

where did i go wrong ?
pls help.