Re: building with gcc 4.4

Milos Jakubicek writes:

> Hi Sam,
> 
> Sam Varshavchik wrote:
>> Milos Jakubicek writes:
>> 
>>> Hi all,
>>>
>>> I'm attaching a tiny patch to make cone building with gcc 4.4, please 
>>> merge it.
>> 
>> Although this looks very straightforward, I do have some questions. 
>> AFAIK, SUSv2 explicitly defines strchr as taking a const char * arg. The 
>> cast should not be necessary.
> 
> Yes, the problem is that starting with gcc 4.4, if strchr takes const 
> char*, it also returns const char*, therefore the cast.
> See http://gcc.gnu.org/gcc-4.4/porting_to.html

I see. In that case, the correct fix is really to redeclare the "p" pointer 
as a const char *, rather than casting it.

> Furthermore, a quick search of the code finds several other
>> instances where both strchr() and memcpy() are used with the same 
>> parameter types, so if these two instances need this kind of a patch, 
>> how come the other instances don't?
> 
> What places, aren't they in an #ifdef so that they do not evaluate?
> Remember that the problem is again the same: you give const char* to 
> strchr => it returns const char*. I'm not sure whether the standard says 
> you can cast any pointer type, even const type, to void*.

That actually explains it. The memcpy in question takes the return value 
from strrchr() with itself takes a const char * parameter, which now makes 
the memcpy parameter a const char *.

The correct fix there, then, would be to const_cast the strrchr() parameter 
to a char *.

Can you verify that the following will make gcc 4.4 happy.

Index: libmail/maildiradd.C
===================================================================
RCS file: /cvsroot/courier/libs/libmail/maildiradd.C,v
retrieving revision 1.6
diff -U3 -r1.6 maildiradd.C
--- libmail/maildiradd.C	24 May 2008 17:57:42 -0000	1.6
+++ libmail/maildiradd.C	19 Apr 2009 11:54:45 -0000
@@ -165,7 +165,8 @@
 	if (flags.size() > 0)
 	{
 		newname = newname + MDIRSEP "2," + flags;
-		memcpy(strrchr(newname.c_str(), '/')-3, "cur", 3);
+		memcpy(strrchr(const_cast<char *>(newname.c_str()), '/')-3,
+		       "cur", 3);
 		// We go into the cur directory, now
 	}
 
Index: libmail/qp.C
===================================================================
RCS file: /cvsroot/courier/libs/libmail/qp.C,v
retrieving revision 1.1
diff -U3 -r1.1 qp.C
--- libmail/qp.C	27 May 2003 14:09:08 -0000	1.1
+++ libmail/qp.C	19 Apr 2009 11:54:46 -0000
@@ -16,7 +16,7 @@
 {
 	static const char xdigits[]="0123456789ABCDEFabcdef";
 
-	char *p=strchr(xdigits, c);
+	const char *p=strchr(xdigits, c);
 
 	if (p == NULL)
 		return -1;

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