c++ allocator 如何自定义

在 C++ 中，自定义分配器（allocator）允许您控制内存分配和释放的方式。要自定义分配器，您需要继承 std::allocator 类并重写其成员函数。以下是一个简单的自定义分配器示例：

#include 
#include 
#include 

template 
class MyAllocator : public std::allocator {
public:
    using value_type = T;
    using pointer = T*;
    using const_pointer = const T*;
    using reference = T&;
    using const_reference = const T&;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;

    template 
    struct rebind {
        typedef MyAllocator other;
    };

    MyAllocator() noexcept {}

    template 
    MyAllocator(const MyAllocator&) noexcept {}

    pointer allocate(size_type n, const void* hint = 0) {
        std::cout << "MyAllocator::allocate("<< n << ")\n";
        return static_cast(std::allocator::allocate(n, hint));
    }

    void deallocate(pointer p, size_type n) noexcept {
        std::cout << "MyAllocator::deallocate("<< p << ", "<< n << ")\n";
        std::allocator::deallocate(p, n);
    }

    size_type max_size() const noexcept {
        return std::numeric_limits::max() / sizeof(T);
    }

    template 
    void construct(U* p, Args&&... args) {
        std::cout << "MyAllocator::construct("<< p << ", " << args... << ")\n";
        std::allocator::construct(p, std::forward(args)...);
    }

    template 
    void destroy(U* p) {
        std::cout << "MyAllocator::destroy("<< p << ")\n";
        std::allocator::destroy(p);
    }
};

int main() {
    std::vector> vec;
    vec.reserve(10);
    for (int i = 0; i < 10; ++i) {
        vec.emplace_back(i);
    }
    return 0;
}