Re: strncpy clarify result may not be null terminated

[Alejandro Colomar <alx@kernel.org>]

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On Thu, Nov 09, 2023 at 12:38:37PM +0100, Alejandro Colomar wrote:
> If you would want to write something based on Michael Kerrisk's article,
> you could do this:
> 
> 	ssize_t
> 	strxcpy(char *restrict dst, char *restrict src, size_t dsize)
> 	{
> 		if (strlen(src) < dsize)

Heh, here's my off-by-one bug of the day.  Good thing is I can fix it in
a single place; unlike calling strncpy(3) all the time.

This should have been <=.

Cheers,
Alex

> 			return -1;
> 
> 		strcpy(dst, src);
> 	}
> 
> You may also want to calculate 'dsize' automagically, to avoid human
> error, in case it's an array, so you could write a macro on top of it:
> 
> 	#define STRXCPY(dst, src)  strxcpy(dst, src, ARRAY_SIZE(dst))
> 
> These are just small wrappers over standard functions, so you shouldn't
> have problems adding them to your project.
> 
> This is my long term plan for shadow-utils, indeed.  I'm first
> transforming strncpy(3) calls into strlcpy(3) to remove the superfluous
> padding, and later will use this strxcpy() to remove the truncated
> strings to avoid misinterpretation.

-- 
<https://www.alejandro-colomar.es/>

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