In C + + programming, the allocator is an important part of the C + + standard library. C + + libraries define a variety of data structures that are collectively referred to as "containers" (such as lists, collection, etc.), one of the common characteristics of these containers, which is that their size can be changed at the time the program is run; In order to do this, it is particularly necessary to perform dynamic memory allocation, where the allocator is used to handle the container's allocation and release requests for memory. In other words, the low-level details of the encapsulated STL container on memory management in the allocator. By default, the C + + standard library uses its own generic allocator, but, depending on the needs, programmers can customize the allocator instead.