On Tue, Sep 19, 2017, at 10:42, Larry McVoy wrote: Random832 replied: Well. It's less useful in one way - it doesn't say what file it was trying to open. You could pass the filename *instead* of "open failed", but that still omits the issue I had pointed out: what were you trying to open the file for (at the very least, were you trying to read, write, or exec it). Ideally the function would have a format and arguments. ==== Exactly. The string interpretation of errno is just another item of data that goes in an error message. There is no fixed place it belongs, and it doesn't always belong there, because all that is error does not fail from a syscall (or library routine). I do often insert a function of the form void errmsg(char *, ...) in my C programs. It takes printf-like arguments. Normally they just get passed to vfprintf(stderr, ...), though sometimes there is something more esoteric, and often fprintf(stderr, "%s: ", progname) ends up in front. But errmsg never knows anything about errno. Why should it? It's supposed to send complaints to a standard place; it's not supposed to invent the complaints for itself! If an errno is involved, I write something like errmsg("%s: cannot open: %s", filename, strerror(errno)); (Oh, yes, errmsg appends a newline too. The idea is to avoid cluttering code with minutiae of how errors are reported.) I don't print the source code filename or line number except for `this shouldn't have happened' errors. For routine events like the user gave the wrong filename or it had the wrong permissions or his data are malformed, pointers to the source code are just unhelpful clutter, like the complicated %JARGON-OBSCURE-ABBREVIATION prefixes that accompanied every official error message in VMS. Of course, if the user's data are malformed, he should be told which file has the problem and where in the file. But that's different from telling him that line 193 of some file he doesn't have and will probably never see contains the system call that reported that he typed the wrong filename. Norman Wilson Toronto ON