From: "ppmoore" <polomora@xxxxxxxxx>
Sent: Tuesday, October 26, 2010 10:17 AM
To: <gcc-help@xxxxxxxxxxx>
Subject: How to force gcc to report a warning/error
Hello,
We had an interesting error that was undetected in gcc:
{
unsigned long a;
unsigned long x=3;
unsigned long y=4;
a =
min(x,y);
}
I've simplified the example. In the original code, the contents of the
min()
statement were longer, so that it was on a separate line from the
assignment
operation.
Because of a bug, the assignment line was removed, and we had the
following
code:
{
unsigned long a;
unsigned long x=3;
unsigned long y=4;
min(x,y);
}
Should this be picked up as a warning/error?
Neither -Wall or -Wextra picked it up.
Many thanks,
Paul
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Hi Paul
The compiler doesn't know if you are purposely ignoring the result of min,
therefore
it doesn't warn you. However, using -Wall in the above code would have
warned you that
'a' was an unused variable.
If you want to make sure that a return value is used, then you can declare
min
using __attribute((__warn_unused_result__)).
For example:
int min(int x, int y) __attribute((__warn_unused_result__));
And compiling would give you the following warning:
warning: ignoring return value of 'min', declared with attribute
warn_unused_result
Regards,
Trevor
