【C++】指针与new的使用

指针

普通指针

基本使用

    //指针p指向t
    int t = 123;
    int*p = &t;
    //C++11以上可用auto
    auto pp = &t;

指针的大小为固定

    int x = 5;
    double y = 100;
    int *px = &x;
    double *py = &y;
    char z = 'z';
    char *pz = &z;
    cout << sizeof(px) << endl;
    cout << sizeof(py) << endl;
    cout << sizeof(pz) << endl;
// 均为8

因此将指针自增加时会根据指向的内容进行自增

    int a[5] = {1,2,3,4,5};
    int *p = a;
    for(int i = 0 ; i < 5 ; i ++ , p ++){
        cout << *p << " ";
    }
    //1 2 3 4 5

new与delete

new用于动态申请存储空间，它比malloc更好
delete用于释放new申请的空间

• new与delete基本使用

    int *x = new int(10);//申请了一个初值为10的整型数据
    int *y = new int;
    cout << *x << " " << *y << endl;
    delete(x); delete(y);

• 数组使用

    int *arr = new int[5];
    for(int i = 0 ; i < 5 ; i ++)cout << arr[i] << " ";
    delete []arr;//注意数组的delete

• 对类使用

class A{
public:
    A(int t){
        this -> x = t;
    }
    int getx(){
        return this->x;
    }   
private:
    int x;

};


int main() {
    A* ptr = new A(5);
    cout << ptr->getx() << endl;
}

注意事项

1.new与delete必须成对使用，delete会释放指针指向的内存但不会删除指针本身

    int* ptr = new int(5);
    delete ptr;
    ptr = new int(6);
    cout << *ptr << endl;
    delete ptr;
    //6

2.不要尝试释放已经释放的内存，delete只能释放new申请的内存

    int* ptr = new int(5);
    delete ptr;
    delete ptr; //不行
    int x = 6;
    int* p = &x;
    delete p; //不行

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