Precision loss with double C++

Question

I'm developing a C++ application that runs on linux environment. I need to store a large value with 6 decimal places. I used a double for that, but after assigning it, it didn't contain the exact value. It was rounded off.

Ex:

double dValue = 79447461534242.913072; //Assignement of value

But after doing that , whenever I see the value of dValue, it is something like 79447461534242.906

Can some one let me know why this is happening and suggest me the correct data type which can hold the exact value without losing any precision.

Answer 1

In a typical implementation, a double has about 15 digits of precision total. It doesn't matter much whether those are before or after the decimal point, it's just a total of 15 digits.

In your case, the original number is about 20 digits, so five are lost immediately.

Answer 2

On linux you can use __float128 which is a quadruple precision floating point type.