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Date: Sat, 6 May 2023 23:55:27 +0600
From: NRK <nrk@...root.org>
To: musl@...ts.openwall.com
Subject: Re: Question: Why vfprintf call twice printf_core?
On Sat, May 06, 2023 at 08:25:25AM +0200, Markus Wichmann wrote:
> If you're looking for performance, however, I suggest steering clear of
> the printf() family of functions. They contain complex logic that is
> typically way overpowered for common needs, and just straight string
> manipulation will always be faster.
Agreed. However...
> E.g. the above call could be turned into
>
> strlcpy(buf, "this is a more typical error message with detail: ", sizeof buf);
> strlcat(buf, "No such file or directory", sizeof buf);
strcat (and friends) are the opposite of performance:
https://en.wikipedia.org/wiki/Joel_Spolsky#Schlemiel_the_Painter.27s_algorithm
Better alternative: have your string copy function return a pointer to the
nul-byte. This pointer can be both used for efficient concat as well as
determining the string length.
Example using POSIX stpcpy(3) (minus bounds checking):
char *p = stpcpy(buf, "this is a more typical error message with detail: ");
p = stpcpy(p, "No such file or directory");
write(2, buf, p - buf);
Additionally, consider getting rid of nul-strings altogether and only
use them in interface boundaries that require them.
- NRK
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