Question

I have simple question about floating number,

double temp;  
std::cout.precision(std::numeric_limits<double>::digits10);
temp = 12345678901234567890.1234567890;
std::cout << (temp < std::numeric_limits<double>::max()) << std::endl;
std::cout << std::fixed << std::endl;
std::cout << temp << std::endl;

However, the output I get is this,

1
12345678901234567168.000000000000000

The value of temp is still within the range of double, however, the value is completely different. I am wondering what have I done wrong here?

Thanks.

Answer 1

A double has only 15.95 decimal digits of precision. You’ve already exceeded this number of digits in the integer part of the value, hence the loss of precision in the last few digits, and the lack of any useful digits after the decimal point.

You should probably take a look at this: http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html before doing any more work with floating point values.