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.

[Skizmo]

string::c_str.

[D_Drmmr]

my problem is to get number of decimals digits after the decimal in a number of type double.

If you use a stringstream, you can call precision to set the number of decimals.

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.

You cannot write to a string like this. If you really want to use the printf function, then you can use a std::vector<char> as a buffer. However, I recommend just using a stringstream.

[Lindley]

my problem is to get number of decimals digits after the decimal in a number of type double.

This is not a well-defined problem in general. Some real numbers may have an infinite number of "digits after the decimal", such as PI or 1/3. Of course, in floating point only a limited number of digits is supported.

Furthermore, because floating point is not exact, even a value which *should* have a finite number of digits after the decimal, like 2.0, may actually be represented by 1.999999999999999999999999.

Therefore, "digits after the decimal" is purely a matter of output formatting. When outputting the value, you instruct the program how many digits to round off to. You should not think of it as an inherent property of the double value.