On 04/09/12 14:50, Leon Timmermans wrote:
On Tue, Sep 4, 2012 at 3:40 PM, Martin J. Evans
<martin.ev...@easysoft.com> wrote:
I recently received an rt (https://rt.cpan.org/Ticket/Display.html?id=79190)
saying some code in DBD::ODBC was wrong and a patch to fix it. The code was:
while (*cp != '\0') {
*cp++ = toupper(*cp);
}
and the fix (which shouldn't be required as the above code is fine) was:
while (*cp != '\0') {
*cp = toupper(*cp);
cp++;
}
The order of execution is undefined if you read a variable and assign
to it in the same (sub)statement. The compiler is allowed to read the
*cp on the right both before the cp++, as the only sequence point is
the semicolon at the end.
Thanks, I did not know that.
The patch as offered does the correct and safe thing of splitting it
up in two statement.
The test code and his results are below. I can obviously avoid this issue
with a simple change to the code but how many other places might this occur?
Do I ignore this (as the reporter is happy to use a newer working compiler)
or do I somehow check for a broken compiler and abort the Makefile? Has
anyone else come across something like this and what did they do?
You fix it. GCC will actually want you against this if you enable
-Wall/-Wsequence-point
Actually, I had tried -Wall but the warning is not issued when -Oanything is
also on the command line (and that happens by default here).
Thanks.
Martin
--
Martin J. Evans
Easysoft Limited
http://www.easysoft.com
