c++ allocator 是否支持对齐分配

C++的allocator模板类本身并不直接提供对齐分配的功能，但是你可以通过自定义分配器来实现对齐分配。自定义分配器可以继承自std::allocator并重载其allocate和deallocate方法，以便在分配和释放内存时考虑对齐要求。

以下是一个简单的示例，展示了如何创建一个支持对齐分配的自定义分配器：

#include 
#include 
#include 

template 
class aligning_allocator : public std::allocator {
public:
    using value_type = T;
    using pointer = typename std::allocator::pointer;
    using const_pointer = typename std::allocator::const_pointer;
    using reference = typename std::allocator::reference;
    using const_reference = typename std::allocator::const_reference;
    using size_type = typename std::allocator::size_type;
    using difference_type = typename std::allocator::difference_type;

    template 
    struct rebind {
        typedef aligning_allocator other;
    };

    pointer allocate(size_type n, const void* hint = 0) {
        pointer result = std::allocator::allocate(n, hint);
        if (result) {
            // Ensure the allocated memory is aligned
            uintptr_t addr = reinterpret_cast(result);
            uintptr_t alignment = alignof(T);
            if (addr % alignment != 0) {
                std::allocator::deallocate(result, n);
                result = std::allocator::allocate(n + alignment - (addr % alignment));
                if (!result) {
                    throw std::bad_alloc();
                }
                std::memset(result, 0, n * sizeof(T));
            }
        }
        return result;
    }

    void deallocate(pointer p, size_type n) noexcept {
        std::allocator::deallocate(p, n);
    }
};

int main() {
    aligning_allocator allocator;
    std::vector> vec;
    vec.reserve(10);

    for (int i = 0; i < 10; ++i) {
        vec.push_back(i);
    }

    for (const auto& elem : vec) {
        std::cout << elem << " ";
    }

    return 0;
}