Question

我对此有点生疏。我试图弄清楚对象声明，值和引用，堆栈和堆到底发生了什么。我知道基础知识，但不确定以下示例：

struct MyObject
{
    int foo;
    MyObject(int val)
    {
        foo = val;
    }  

    MyObject()//[EDIT] default constructor
    {
    }
}

//...

//1)
//this reserves memory on the stack for MyObject0 and initializes foo:
MyObject a = MyObject(1); //[EDIT] fixed from comments

//2)
MyObject* b = new MyObject(2);//This I know reserves memory on the heap,  
//returns a pointer to it (and calls constructor). 
//There are also other ways like malloc or memset.

//3)
MyObject c = *(new MyObject(3));// So here we instantiate MyObject on the heap, 
//return a pointer to it but the pointer is dereferenced outside the parenthesis. 
//Is c now a newly created value type copy on the stack? 
//And is the original new MyObject(3) now inaccessible in the heap memory (leaked) 
//because the pointer to it was never stored?

//4)
// void myFunc( MyObject c){}
myFunc(c); //Am I doing a member-wise assignment from c to a new function-scope 
//temporary MyObject reserved somewhere else in memory (in a stack frame?)? 
//Or am I somehow passing a reference to c even though c is not a pointer or reference?
//[EDIT] myFunc(c); would pass as a reference if I had void myFunc( MyObject &c){}

最后，如果我有一个MyObject[] myObjArr1 = new MyObject[10]()我在堆上有10个未初始化的MyObject结构，并且堆上还有一个类型为MyObject Array的指针。

如何在堆栈上声明MyObject数组，其中数组中的MyObject结构也在堆栈中？或者这不是你做的事情？

Answer 1

让我以更精确的方式重新评论：

1）这会在堆栈上创建一个a变量，并使用临时MyObject(1)的值初始化它，该值在堆栈上创建为MyObject调用MyObject::MyObject(1)作为构造函数。编译器可以消除中间步骤。您只需MyObject a(1);注意：=不是作业

2）通过调用MyObject在堆上创建MyObject::MyObject(2)并返回指向它的指针，用于初始化b指针。

忘记malloc和memset：他们分配内存，但不要忘记内容 CONSTRUCT对象。你越早忘记它们，对你来说就越好和其他任何人。

3）在堆上创建Myobject并通过调用Myobkect::Myobject(3)构造，然后取消引用new返回的指针，并将结果值用于初始化c复制。堆上创建的对象被遗忘了＃34;在那里。（内存泄漏：你没有机会进一步访问它）

4）对象c被复制到c的本地参数myFunc中（实际上两个c是两个不同的对象）将存在于堆栈中直到功能退出。

堆栈和堆上的C ++结构和数组，值，引用和解引用问题

1 个答案: