As one example, a lot of the libraries referenced in the book have gone through major version changes (1.x to 2.x etc.) that change the functions being exported and/or architecture reworks changing which libraries you need to import which means that if you try to copy + compile a lot of the code snippets, they will not compile. It is generally trivial changes in most cases, but if you are a newbie to the language, it is likely not immediately obvious because you will think you copied from the book wrong (or that the book has a typo) instead of the libraries having been changed.
There is also a lot written about historical quirks you will come across that have since been fixed.