...what? What are you talking about? In what world would a compiler implement a preprocessor directive to ever use an llm, the internet, or your credit card details (from where would it get those)??? There are always implementation defined things in every language, for example, ub behavior. Do you get worried that someone will steal your bitcoin every time you use after free? Of course not! Even in Python when you OOM -- at least in CPython -- you crash with undefined behavior.

This doesn't sound like the kind of portability anyone is really worried about. I get that the docs on the linked site are written in standards-ese and are complicated by macro replacement, but I don't think the outcome of sending your credit card details away is gonna be an outcome. If it was, an uncharitable implementation with access to your card details would be free to do that any time you gave it input invoking undefined behaviour (which is of course not uncommon, especially in incorrect code).

If you want to remain portable, write your code in the intersection of the big 3 - GCC, Clang and MSVC - and you’ll be good enough. Other implementations will either be weird enough that many things you’d expect to work won’t or are forced to copy what those 3 do anyway.

You're not the only one who feels that way, but IMHO it's not avalid complaint.

The C++ standard says implementation defined because the weeds get very thick here:

- Are paths formed with forward slash or backslash?

- Case sensitive?

- NT style drive letter or Posix style root dir?

- For relative paths, what is it relative to? When there all multiple matches, what is the algorithm to determine priority?

- What about symlinks and hard links?

- Are http and ftp URI's supported (e.g. an online IDE like godbolt). If so, which versions of those protocols? TLS 1.3+ only? Are you going to accept SHA-1?

- Should the file read be transactional?

People already complain that the C++ standard is overly complicated by one or two orders of mangitude more than it should be. So instead of adding even more complexity by redefining the OS semantics of your build platform in a language spec, they use "implementation defined" as a shorthand for "your compiler will call fopen" plus some implementation wiggle room

What if steals my credit card data is a pointless strawman. If a malicious compiler dev wanted to steal your credit card data, they'd just inject the malicious code; not act like a genie, searching the C++ spec with a fine comb for a place where they could execute malicious code while still *technically* being stanards conformant. You know that, I know what, we all know that. So why are we wasting words discussing it?

It's still lacking content that goes before/after the output.

Just write a Python script that does the whole thing.