<b>浮点数的格局化</b>[VC/C++编程]

string do_fraction(long double value, int decplaces=3)

char DECIMAL_POINT='.';

int prec = numeric_limits<long double>::digits10; // 18

out.precision(prec);//override default

out << value;

string str= out.str(); //extract string from stream

size_t n=str.find(DECIMAL_POINT);

if ((n!=string::npos) //is there a decimal point?

　　&& (str.size()> n+decplaces)) //is it followed by at

　　　//least decplaces digits?

{

　　str[n+decplaces]='';//overwrite first redundant digit

}

str.swap(string(str.c_str()));//get rid of spurious

//characters after the nul
return str;

}

如

cout << do_fraction(123456789.69999001) << endl;
cout << do_fraction(12.011) << endl;

输出

123456789.69
12.01