[Bug manual/1997] opern_memstream() buffer should be freed

["michael dot kerrisk at gmx dot net" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From michael dot kerrisk at gmx dot net  2005-12-13 09:05 -------
Subject: Re:  opern_memstream() buffer should be freed

> Von: "decimal at us dot ibm dot com" <sourceware-bugzilla@sourceware.org>

> I took a look in the linux man pages and in the glibc manual and I found
> that while the man page for strdup(3) does say
> 
>   The  strdup()  function  returns  a  pointer to a new string which is a
>   duplicate of the string s.  Memory for the new string is obtained with
>   malloc(3), and can be freed with free(3).
> 
> the glibc manual info entry for strdup() says
> 
> This function copies the null-terminated string s into a newly allocated
> string.
> The string is allocated using malloc; see Unconstrained Allocation. If
> malloc
> cannot allocate space for the new string, strdup returns a null pointer.
> Otherwise it returns a pointer to the new string.
> 
> The section on Unconstrained Allocation includes a section "Freeing after
> Malloc" which discusses free().
> 
> The current section in the glibc manual on open_memstream() says
> 
> This function opens a stream for writing to a buffer. The buffer is
> allocated
> dynamically (as with malloc; see Unconstrained Allocation) and grown as
> necessary.
> 
> So is it really necessary to explicitly mention free() next to every
> function
> which uses malloc()? I'm asking to see if anyone else has a strong
> opinion.

Being the Linux manual page maintainer (but I didn't write that 
strdup(2)) text, I'm inclined to the view that it is useful
to mention free() when describing these interfaces. It is just 
too easy to create memory leaks in C: giving people more direct 
hints (instead of suggesting a hyperlink in the doc, in which it
only becomes clear that free() is needed after quite a bit of 
reading) alerts people to the issue.  

There is a second reason for doing this in the case of 
open_memstream(): the interface is non-standard.  I can determine
from any number of places (my own knowledge, the SUSv3 spec, 
manual pages on various systems) that glibc's strdup() must be 
followed with a free().  However, those sources of information
are not available for open_memstream().

I realise there are differences on documentation philosophy for 
"info" and the manual pages, but I do think an explicit mention of 
free() could be valuable here (and perhaps in a few other places).

Cheers,

Michael



-- 


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