GCC, functions, and pointer arguments, warning behaviour

Question

I've recently updated to a testing distribution, which is now using GCC 4.4.3. Now I've set everything up, I've returned to coding and have built my project and I get one of these horrible messages:

*** glibc detected *** ./boxyseq: free(): invalid pointer: 0x0000000001d873e8 ***

I absolutely know what is wrong here, but was rather confused as to when I saw my C code where I call a function which frees a dynamically allocated data structure - I had passed it an incompatible pointer type - a pointer to a completely different data structure.

warning: passing argument 1 of 'data_A_free' from incompatible pointer type
note: expected 'struct data_A *' but argument is of type 'struct data_B *'

I'm confused because I'm sure this would have been an error before and compilation would never have completed. Is this not just going to make life more difficult for C programmers?

Can I change it back to an error without making a whole bunch of other warnings errors too?

Or am I loosing the plot and it's always been a warning?

if you know how to make this in particular an error, please post. It's covered by -pedantic-errors, but that's broader. — Matthew Flaschen
– Matthew Flaschen, Commented Jun 3, 2010 at 8:06
@Matthew so it has always been a warning? If I find out I'll post, but a quick search through gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Warning-Options.html didn't reveal anything. — James Morris
– James Morris, Commented Jun 3, 2010 at 8:10

Daniel Stutzbach · Accepted Answer · 2010-06-03 13:38:54Z

2

It's always been a warning. C allows you to implicitly cast any pointer to any other pointer, although any half-decent compiler will warn you.

It's an error in C++, though. Perhaps that's what you were thinking of?

In GCC, you can turn a warning into an error using -Werror=, but I don't see an option for this particular warning. You could just use -Werror to turn all warnings into errors, but that might do more than you want.

answered Jun 3, 2010 at 13:38

Daniel Stutzbach

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Comments

Andrew McGregor · Accepted Answer · 2010-06-03 08:11:35Z

0

This is definitely one of the things that the clang analyzer would catch, and therefore you can make it an error building with clang.

answered Jun 3, 2010 at 8:11

Andrew McGregor

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2 Comments

Matthew Flaschen Over a year ago

You can make it an error with gcc too (-pedantic-errors). The question is can you avoid making a bunch of other warnings errors.

James Morris Over a year ago

Eurrgghh, just read the wikipedia page about it: "Its goal is to offer a replacement to the GNU Compiler Collection (GCC). Development is sponsored by Apple..." no thanks.

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