Talk:C dynamic memory allocation

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Sunmist3 (talk) 22:00, 6 July 2016 (UTC)

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"heap", "free store", etc.

Neither C90 nor C99 nor C11 nor C18 appear to indicate that there is a given region containing all memory allocated by malloc(), calloc(), realloc(), or aligned_alloc(). For example, an implementation could, conceivably, allocate objects larger than the page size used by the OS from one region of the address space, by rounding up the size to a multiple of a page size and allocating n/page_size pages aligned on a page boundary, and could allocate smaller objects from a separate pool of memory. (If I remember correctly, the Darwin memory allocator works that way.)

So allocating from a "heap" is best thought of as meaning "these allocations come from one or more places, and all of those places, considered together, constitute a 'heap'".

Note also that none of those standards use the term "heap".

(The term "heap" predates both C and Unix; it dates back at least as far as Algol 68, the Report for which says, in section 5.2.2 "Generators", that

In an answer to a StackOverflow question "What is the origin of the term 'heap' for the free store?", somebody notes that even K&R, Second Edition, didn't use the term "heap":

So perhaps neither "free store" nor "freestore" nor "heap" should be used here, as this is about C.

As for C++, C++2017 uses the phrase "free store" in three places:

• on page 1, it says "In addition to the facilities provided by C, C++ provides additional data types, classes, templates, exceptions, namespaces, operator overloading, function name overloading, references, free store management operators, and additional library facilities.", where I assume "free store management operators" means new and delete;
• section 15.5 "Free store", on pages 289 to 291, uses it in the section title but doesn't seem to say what "free store" is;
• the index has, on page 1518, an entry "free store, see also new, delete, 289".

So I'm not even sure what should be said about C++.

(Darwin also offers a set of "zone" routines that take a malloc_zone_t * as an argument, where a "zone" is allocated with malloc_create_zone() and destroyed, along with everything allocated in it, with malloc_destroy_zone(). malloc_default_zone() returns the zone from which malloc() etc. allocate memory, so, at least on Darwin, I guess you could say that stuff is allocated from a "zone".

However, none of that is a reason to use "zone" here, unless it's commonly used in platforms that aren't Darwin-based.) Guy Harris (talk) 06:29, 27 July 2022 (UTC)

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The above message was substituted from Template:Tlc by PrimeBOT (talk) on 19:56, 1 February 2023 (UTC)

It is the compiler not glibc

The article says that glibc limits allocation up to 2^(CHAR_BIT * sizeof(ptrdiff_t) - 1) - 1 . This is a compiler limitation, GCC generates non-sense (by design cannot deal with objects bigger than ptrdiff_t) for any allocation over that value, clang DCEs the code because "it can never succeed".. 181.160.10.238 (talk) 22:23, 4 October 2023 (UTC)