C++内存(内存池)管理讲解

内存管理的目的：提高速度，降低空间浪费率

减少malloc的使用。（可以先分配一大块，再一点一点的使用） 较少cookie的使用。

#include 

using namespace std;

class Screen {
public:
    Screen(int x):i(x) {}
    int get() { return i; }

    void* operator new(size_t);
    void operator delete(void*, size_t);

private:
    Screen* next; // 为了去掉cookie
    static Screen* freeStore;
    static const int screenChunk;
private:
    int i;
};

Screen* Screen::freeStore = 0;
const int Screen::screenChunk = 24; // 创建24份，内存池

void* Screen::operator new(size_t size) {

    Screen* p;
    if (!freeStore) {
        std::cout << "operator new" << std::endl;
        //linked list是空的，所有申请一大块
        size_t chunk = screenChunk * size;
        freeStore = p = reinterpret_cast (new char[chunk]);

        //将一大块分割成片，当做linked list串接起来
        for (; p!=&freeStore[screenChunk-1]; ++p) {
            p->next = p + 1;
        }
        p->next = 0;
    }
    p = freeStore;
    freeStore = freeStore->next;
    return p;
}

void Screen::operator delete(void* p, size_t) {
    //将deleted object 插入free list前端
    (static_cast(p))->next = freeStore;
    freeStore = static_cast(p);
}

int main() {
    cout << sizeof(int) << endl;
    cout << sizeof(Screen) << endl;

    size_t const N = 100;
    Screen* p[N];

    for (int i = 0; i < N; ++i) {
        p[i] = new Screen(i);
    }

    //输出前10个指针，比较其间隔，确认其没有cookie
    for (int i = 0; i < 10; ++i) {
        cout << p[i] << endl;
    }

    for (int i = 0; i < N; ++i) {
        delete p[i];
    }
    return 0;
}