Re: memory deallocation
Re: memory deallocation
- Subject: Re: memory deallocation
- From: Dave Carrigan <email@hidden>
- Date: Sat, 4 Apr 2009 15:09:52 -0700
On Apr 4, 2009, at 2:35 PM, Daniel Luis dos Santos wrote:
Hello,
From what I know so far, memory allocated using the malloc() family
of functions is freed using the free() function. Literal values such
as :
char *aString = "some text";
are automatic values and are deallocated by the compiler
automatically.
In actual fact, they are neither allocated nor deallocated. String
literals are stored in a section executable itself, and the compiler
just initializes the aString pointer have the address of that literal.
When I free some pointer that was allocated as in the example
declaration above I get a warning that a non page-aligned, non
allocated pointer is being freed.
Yup, don't do that. You're attempting to free something that was never
malloc'ed.
Then in practical terms, what does a literal value such as a #define
that is used to initialize pointers such as the one above serves for ?
#define is a different thing altogether. The C compiler never sees
#defines; by the time the C compiler is processing that code, all
macros have been evaluated and that is what the C compiler sees.
Thus, the following two things are identical as far as the C compiler
is concerned.
#define STR "string"
char* str = STR;
---
char* str = "string";
If for example I have a group of string #defines that are used in
log messages, that means that I will have to malloc space for them
the sprintf them to it, so I can be sure that I don't get that
warning when deallocating the log messages.
You don't have to dealloc them, ever.
when you pass as pointer to bytes (like a void*) to cocoa (for
example NSData), what does it do ? It copies the bytes or just
copies the pointer ?
It just copies the pointer.
This is basic C (no cocoa or anything involved). I strongly recommend
that you find a good C book that talks about pointers and how they
work. You will save yourself years of grief and unexplained bugs if
you understand pointers now; they are the most critical concept in C
and if you don't understand them, you will never be a good C (C+
+,Objective-C) programmer.
--
Dave Carrigan
email@hidden
Seattle, WA, USA
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