3 ms·

Bad implementation*, not so much a wholly bad idea. Being sometimes a macro, sometimes not, not threadsafe? And more.

• tzahola 9y ago
  Well... Yeah, there's some merit to errno: it lets you handle errors. Otherwise it's a horrible piece of crap: - It's a global (sorry, thread-local) variable, updated behind the scenes. - You can't tell whether a function will update errno or not by its signature. You have to consult the documentation. - You can't tell the range of possible errno values unless it's explicitly documented (and the documentation is kept in sync with the implementation). - Errno only communicates error metadata; the success/error bit has to be communicated in-band via the return value (e.g. printf returning < 0). - Except for some functions which return void (or like readdir, which returns NULL when reaching the end of the directory, or on error) and set errno on error. - In which case you better set errno to 0 before calling the function, because while these functions set errno on failure, they not necessarily set it to 0 on success...