What is the difference between a file descriptor and a file descriptor?

Question

*nix-like systems

I do not understand what and how. Is there a working code where it can be felt and touched?
Sometimes it is not clear what is copied to the child process from the parent

Answer 1

There is no difference. That's right - a file descriptor.
It's just a number - the ID of a particular I/O thread.
In Unix, under descriptors 0, 1, 2 for each process, STDIN, STDOUT, STDERR are usually immediately opened by default.

Answer 2

This is a process at the end of which a result is returned. For example, the code is executed and exit 0
comes at the end . The answer is that everything went well. In short, it is a return from a function or value code about the status of the operation. Often used in permissions handling events. For example, if you request access to a file and the system response is 0, then everything is fine with access. If 1 is not available. The existence of the file is also checked. This is conditional. In the program, you can implement this in any way. How much fantasy is enough.