Determine if a float number is irrational of a fraction

I have a random float number and I have to determine if it is an irrati开发者_开发技巧onal number like √2 or a fraction like 123/321. Both of them are represented like an endless set of numbers anywhere but is there any way to definitely say whether a number is a fraction or it's irrational?

Thank you!

All floating point numbers are rational because the mantissa has a fixed length. Irrational numbers stored in floating point are truncated into rational numbers.

If you have a specific list of numbers you need to match, you can compare the random number to numbers on the list at a set floating point precision, but do keep in mind that you will get false positives due to truncation or rounding.

All (finite, non-NaN) floating point values are rational, because all finite (binary) floating-point numbers are of the form f*2^e for integers f and e.