Date: Thu, 14 May 2020 23:18:10 +0300 From: Yuri Pankov <ypankov@fastmail.com> To: Polytropon <freebsd@edvax.de>, FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: Multi-line text output via printf() et al. Message-ID: <0d78f2bb-4169-c1ba-48c0-3f9c6993c961@fastmail.com> In-Reply-To: <20200514220904.7a4c1e28.freebsd@edvax.de> References: <20200514220904.7a4c1e28.freebsd@edvax.de>
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Polytropon wrote:
> In the FreeBSD sources, there are several ways shown about
> how to emit several lines of text to the console or to a
> file. Allow me to phrase the question in C, even though
> it will be a valid question in almost every other programming
> language (compiled or interpreted):
>
> What is the _proper_ way of printing multiple lines?
>
> My research basically did bring up the following methods:
>
> a) multiple function calls:
>
> printf("This is the first line of text.\n");
> printf("And this is the second line.\n");
> printf("Finally a third line.\n");
>
> b) one string in multiple parts in one function call:
>
> printf("This is the first line of text.\n"
> "And this is the second line.\n"
> "Finally a third line.\n");
>
> c) multiple lines in one string:
>
> printf("This is the first line of text.\n
> And this is the second line.\n
> Finally a third line.\n");
>
> There is a specific restriction that if a string contains
> conversion specifications for variables, those have to be
> in the 1st argument, so printf() does not print several
> strings as individual arguments except there's a first
> one containing appropriate %s entries. This applies for
> any string containing %<something>: it has to be in the
> first argument passed to printf().
>
> d) multiple strings with format string:
>
> printf("%s%s%s",
> "This is the first line of text.\n",
> "And this is the second line.\n",
> "Finally a third line.\n");
>
> In this case, the \n could be in the format string instead
> of the text lines.
>
> So, what's the correct (or at least recommended way) of
> doing this? Think about use cases like fprintf(stderr, ...)
> for things like usage messages, or printing to a file for
> multi-line entries.
b) and d) are what I see the most in the code, b) mostly in illumos
(solaris) codebase and d) in FreeBSD codebase. I just checked how some
utilities print their usage messages (as that's where you'd expect
multiline strings):
https://svnweb.freebsd.org/base/head/bin/cp/utils.c?revision=326025&view=markup#l550
https://svnweb.freebsd.org/base/head/bin/mv/mv.c?revision=326025&view=markup#l506
https://svnweb.freebsd.org/base/head/bin/ln/ln.c?revision=326025&view=markup#l352
I've also seen a); c) looks completely weird to me.
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