Re: Error in manual page memcpy(3)

Alejandro Colomar <[email protected]> Thu, 4 Jun 2026 13:03:03 +0200

Newsgroups	org.kernel.vger.linux-man
Message-ID	<aiFagMMoVEGdlJop@devuan>

Hi Siegfried,

On 2026-06-04T12:14:08+0200, Siegfried Ehlert wrote:
> An error has crept into the synopsis of the *memcpy(3)* manual page.
> Immediately after the opening bracket of the function name, the third
> argument is listed as "size_t n;". The same applies to the strncpy(3) and
> stpncpy(3) manual pages; there, too, the third argument appears immediately
> after the opening bracket.
> 
> *Example:
> *
> 
> 
>    SYNOPSIS
> 
> *#include <string.h>* *void *memcpy(*size_t n; *void */dest/*[restrict
> */n/*], const void */src/*[restrict */n/*],* *size_t */n/*);*

That's correct.

     void *memcpy(size_t n;
                  void dest[restrict n], const void src[restrict n], size_t n);

What you're seeing is a forward declaration of the third parameter.
This is necessary so that it can be used in the array length expressions
in the declarators of the first and second parameters, since the third
parameter hasn't been declared yet.  This is an old GNU extension, and
is documented at the bottom of this page of the GCC manual:
<https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html>

Have a lovely day!
Alex

> 
> Kind regards
> Siegfried

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

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