On Tue, Oct 31, 2017 at 2:00 PM, Steve D'Aprano <steve+pyt...@pearwood.info> wrote: > Python has no GOTO, fortunately, but C has at least two, GOTO and LONGJMP. A C > macro could, if I understand correctly, jump into the middle of another > function. (Yay for spaghetti code!)
No, I don't think you do understand them correctly - or at least, I don't know of any way for a C macro to jump into the middle of a function. There are three quite different things mentioned here. 1) The 'goto' statement, which unconditionally jumps you to another location *in the same function* 2) setjmp/longjmp, which is not actually a "goto", but more of a "multi-level return" 3) Preprocessor macros, which expand to some form of C source code. Since macros have to expand to legal C code, they can't do anything that you couldn't do by simply writing out the code - they just hide it behind a token that looks like a function call. To use setjmp/longjmp (which, btw, are actually standard library functions, not language features) to jump into another function, you first have to call the destination; they're much more akin to exception handling than to an unstructured 'goto' (in fact, they're often used in the implementation of exception handling). Basically, longjmp can only rewind you to a previous setjmp, and only if the function that called setjmp has *not returned* - so you can only use it to jump outwards, not inwards. But feel free to point out something I've forgotten, wherein you can actually jump into the middle of a function using a macro. There's enough dark corners in C that it's entirely possible I've missed something obvious. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
