Date: Sun, 21 Feb 1999 16:37:20 +1100 From: Bruce Evans <bde@zeta.org.au> To: freebsd-current@FreeBSD.ORG, hibma@skylink.it Subject: Re: const char * Message-ID: <199902210537.QAA13128@godzilla.zeta.org.au>
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>../../dev/usb/ukbd.c: In function `ukbd_detach':
>../../dev/usb/ukbd.c:373: warning: cast discards `const' from pointer
>target type
>...
>It is a consequence of the following type definition:
>
>(sys/bus_private.h)
>struct device {
>...
> const char* desc; /* driver specific description */
>...
>}
>
>One problem I have is that a string like that might be produced by
>concatenating a few strings together. In the case of USB the desc is
>the string returned by the device. At attach the string is created and
>malloc()-ed, at detach free()-ed.
At the <sys/bus*.h> (bus) level, `desc' is just a string. It is const
mainly so that callers can pass a literal string to device_set_desc()
without getting a warning from -Wcast-qual. Unfortunately, this prevents
the bus level from helping you keep track of how the string was created.
The warning could be avoided using a table of the original (non-const)
addresses of the (malloc()ed) strings passed to device_set_desc().
This is a bit much to avoid a harmless warning, but you would need to
do it if not all strings were malloc()ed.
The warning can be avoided by (ab)using a variant union. I plan to use
a suitably macroised version of this to fix warnings for library functions.
Bruce
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