Comment by marcosdumay

It's not an overwhelming hard problem. There are some issues with radix signaling, exponent notation, decimal points being allowed or not, and group separators that make parsing numbers incredibly irritating. So you usually don't want to do it yourself.

But it's not hard at all. It's not even as full of small issues that you can't handle the load, like dates. It's just annoying as hell.

The problem is exclusive to C and C++. It's created by the several rounds of standardization of broken behavior.