GCC如何实现C ++标准分配器？

Question

I am not familiar with tracking down the source codes to figure out the GCC STL implementation (libstdc++) of the C++ standard allocator, and I cannot find any brief explanation, documentation and technical reports that describe what the memory model that GCC selects.

I guess that GCC uses several fixed-size buckets for storing small objects of the same size in bytes and allocate large memory space ad hoc for large objects over the specific size.

What is the specific memory model that GCC selects for the C++ standard allocator?

Answer 1

I cannot find any brief explanation, documentation and technical reports that describe what the memory model that GCC selects

Read the code. It's open source, and it's included with the compiler as plain text.

If you're not sure where your standard headers are, you can do one of two things:

1. learn how to ask the compiler as in this question

2. trick the compiler into telling you, eg. by trying to do something std::allocator cannot

    #include <memory> int main() { std::allocator<int> a; a.allocate(&a); return 0; } 

   gives

    error ... In file included from \\ /usr/include/x86_64-linux-gnu/c++/6/bits/c++allocator.h:33:0, 

When you find out that std::allocator just uses the heap to make all those decisions, you can look at the glibc source for malloc .

Answer 2

std::allocator just uses operator new and operator delete , and those in turn simply wrap malloc and free .

Thus the implementation is delegated to the C library, whichever happens to be in use.