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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Why does C allow structs to have a tag?
Date: Wed, 11 Aug 2021 11:41:23 -0700
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scott@slp53.sl.home (Scott Lurndal) writes:
> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>On Wednesday, 11 August 2021 at 14:52:54 UTC+1, Scott Lurndal wrote:
>>> 
>>> strcat is almost never the right interface to use. It needs 
>>> to scan the entire string to find the terminal nul-byte before 
>>> appending. As the string gets longer, each strcat takes longer 
>>> than the one before. 
>>> 
>>> Just keep a pointer to the next element and increment the 
>>> pointer each time you add a new element.
>>>
>>Most strings are short. Building up a url with strcat is not going to
>>stress a 3GHz machine. If the strings become huge then, yes, you
>>need to look at more efficient ways of concatenating them.
>
> Building it with snprintf() will be far more flexible and efficient.
>
> Every cycle matters.

As Bart's measurements indicate, snprintf() is likely to have
substantial overhead, probably because it has to parse its format
string.  I wouldn't assume snprintf() is going to be faster than
strcat() without measuring it for the specific data I'm working with.

The non-standard strlcat() returns the initial length of the destination
plus the length of the source, which can be used to find the end of the
copyied string without re-scanning.  (It can be a little tricky to get
the compilation command right on some systems.)

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */