Custom allocator in std::vector

Question

Is it possible to use custom allocator for std::vector internal allocations? If yes, how?

template < class T, **class Allocator = allocator** > class vector; — Luchian Grigore, Aug 10 '12 at 07:08
First google link - http://www.josuttis.com/libbook/memory/myalloc1.cpp.html and http://www.josuttis.com/libbook/memory/myalloc.hpp.html — Luchian Grigore, Aug 10 '12 at 07:11
See this recent answer by Howard Hinnant: http://stackoverflow.com/a/11703840/819272 — TemplateRex, Aug 10 '12 at 07:20
What do you mean by "internal allocations"? What aspect of the vector's allocator concept is unclear? — Kerrek SB, Aug 10 '12 at 08:21
@KerrekSB If I am not mistaken, `vector` calls `new` / `delete` internally when the size changes. Those (de)allocations were meant by the word 'internal'. — Cartesius00, Aug 10 '12 at 09:56
@James: No. `vector` calls `alloc.allocate()` and `alloc.deallocate()` when the size changes. — Kerrek SB, Aug 10 '12 at 10:02

bitmask · Accepted Answer · 2018-06-18T12:28:07.467

20

You basically have to implement your allocator type to conform to the Allocator concept.

The linked page lists all requirements of that type, but the core functionality is implemented in the allocate member function.

edited Jun 18 '18 at 12:28

answered Aug 10 '12 at 07:13

bitmask

26

could you give an example – serup May 15 '18 at 11:03
@serup Click on the link, it has tons of examples. – bitmask May 15 '18 at 11:38
9

This is exactly the reason why link only answers are *bad*! The page doesn't exist anymore. Pointing towards examples in the broken link is even worse. – dtell Jun 18 '18 at 12:03
2

At least I updated the link. The new page is referenced, as cppreference is a wiki. But your point is taken. – bitmask Jun 18 '18 at 12:29
5

Here is a [running example](https://godbolt.org/z/7fnj1rGr9) derived from the [reference](https://en.cppreference.com/w/cpp/named_req/Allocator). – schoetbi Oct 27 '21 at 05:49

1 Answers1