Issue 17042: Example in C-API memory management doc has confusing order (original) (raw)

This issue has been migrated to GitHub: https://github.com/python/cpython/issues/61244

classification

process

Created on 2013-01-26 18:20 by eric.snow, last changed 2022-04-11 14:57 by admin. This issue is now closed.

Messages (5)
msg180697 - (view)	Author: Eric Snow (eric.snow) *	Date: 2013-01-26 18:20
In http://docs.python.org/dev/c-api/memory.html#examples: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv char *buf1 = PyMem_New(char, BUFSIZ); char *buf2 = (char *) malloc(BUFSIZ); char *buf3 = (char *) PyMem_Malloc(BUFSIZ); ... PyMem_Del(buf3); /* Wrong -- should be PyMem_Free() */ free(buf2); /* Right -- allocated via malloc() */ free(buf1); /* Fatal -- should be PyMem_Del() */ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Is there a good reason to have the second set of 3 lines in the opposite order as the first three? At first I missed that they were in a different order and thought there was an error in the example. If there's no good reason for the order, it would be worth fixing. If there is a good reason, a comment in the example would help. Either way I'd be glad to patch it (will go ahead with fixing the ordering later today if no one does it first).
msg180698 - (view)	Author: Stefan Krah (skrah) *	Date: 2013-01-26 18:36
Please don't change this: It's a common pattern in C to undo memory allocations in the opposite order.
msg180719 - (view)	Author: Eric Snow (eric.snow) *	Date: 2013-01-26 22:58
Thanks for clarifying, Stefan. Are you opposed to a comment in the example?
msg180722 - (view)	Author: Stefan Krah (skrah) *	Date: 2013-01-26 23:55
Moderately opposed, yes. PyMem_Malloc()/PyMem_Free() and PyMem_New()/PyMem_Del() are already explained in depth above.
msg180724 - (view)	Author: Eric Snow (eric.snow) *	Date: 2013-01-27 00:14
Sorry, I'd meant something like this: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv char *buf1 = PyMem_New(char, BUFSIZ); char *buf2 = (char *) malloc(BUFSIZ); char *buf3 = (char *) PyMem_Malloc(BUFSIZ); ... /* in reverse order */ PyMem_Del(buf3); /* Wrong -- should be PyMem_Free() */ free(buf2); /* Right -- allocated via malloc() */ free(buf1); /* Fatal -- should be PyMem_Del() */ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This will help if someone does not know the common pattern.