C++ allocator作用 自定义内存分配实现

free

自定义Allocator在std::vector中的应用

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自定义allocator可以与STL容器（如

std::vector

#include 
#include 
#include 

// 假设你已经定义了一个内存池类 MemoryPool
class MemoryPool {
public:
    MemoryPool(size_t blockSize, size_t blockCount) : blockSize_(blockSize), blockCount_(blockCount) {
        // 初始化内存池
        memory_ = malloc(blockSize_ * blockCount_);
        if (!memory_) {
            throw std::bad_alloc();
        }
        freeBlocks_ = static_cast(memory_);
        for (size_t i = 0; i < blockCount_ - 1; ++i) {
            *reinterpret_cast(freeBlocks_ + i * blockSize_) = freeBlocks_ + (i + 1) * blockSize_;
        }
        *reinterpret_cast(freeBlocks_ + (blockCount_ - 1) * blockSize_) = nullptr;
    }

    ~MemoryPool() {
        free(memory_);
    }

    void* allocate() {
        if (!freeBlocks_) {
            return nullptr; // 内存池已满
        }
        void* block = freeBlocks_;
        freeBlocks_ = *reinterpret_cast(freeBlocks_);
        return block;
    }

    void deallocate(void* block) {
        *reinterpret_cast(block) = freeBlocks_;
        freeBlocks_ = static_cast(block);
    }

private:
    size_t blockSize_;
    size_t blockCount_;
    void* memory_;
    char* freeBlocks_;
};

template 
class PoolAllocator {
public:
    using value_type = T;

    PoolAllocator(MemoryPool& pool) : pool_(pool) {}
    template  PoolAllocator(const PoolAllocator& other) : pool_(other.pool_) {}

    T* allocate(std::size_t n) {
        if (n != 1) { // 简化：只分配单个对象
            throw std::bad_alloc();
        }
        void* p = pool_.allocate();
        if (!p) {
            throw std::bad_alloc();
        }
        return static_cast(p);
    }

    void deallocate(T* p, std::size_t n) {
        if (n != 1) { // 简化：只释放单个对象
            return;
        }
        pool_.deallocate(p);
    }

private:
    MemoryPool& pool_;
};

template 
bool operator==(const PoolAllocator& a, const PoolAllocator& b) {
    return &a.pool_ == &b.pool_;
}

template 
bool operator!=(const PoolAllocator& a, const PoolAllocator& b) {
    return !(a == b);
}


int main() {
    MemoryPool pool(sizeof(int), 10);
    std::vector> vec({1,2,3}, PoolAllocator(pool));

    for (int i = 0; i < vec.size(); ++i) {
        std::cout << vec[i] << " ";
    }
    std::cout << std::endl;

    return 0;
}

这个例子展示了如何使用一个简单的内存池分配器来管理

std::vector

std::array