C ++动态分配 [英] C++ dynamic allocation

问题描述

假设我们有一个班级A

班级A 
 {
 // blabla 
 public int x; 
} 

当我们这样做时：

 A a =新的A（）; 

是动态分配的x吗？

解释会很棒。谢谢



我尝试了什么：



我认为是动态完成，因为我们需要抛出对象来访问x。

解决方案

只有非静态成员变量存储在分配的内存块中。在您的示例中，内存仅包含 x 成员，因此至少具有 int 的大小。



您可以通过打印地址来验证这一点：

 A类
 {
 public： 
 A（）{x = 0; } 
 int x; 
}; 
 
 int main（）
 {
 A * a = new A（）; 
 printf（A的大小=％lu \ n，sizeof（* a））; 
 printf（a =％p \ n的地址，a）; 
 printf（a-> x =％p \ n的地址，& a-> x）; 
返回0; 
} 

可能打印

 A的大小= 4 
 a的地址= 0x602010 
地址a-> x = 0x602010 

另请注意我的示例中使用的正确语法（类定义必须以分号结尾， a 是一个指针）。

你可以在堆栈上创建对象，也可以在堆上动态创建。

在堆栈上：

  void  myFunc（）
 {
 A a ; 
} 

只要执行myFunc，现在就存在a。



动态堆栈：

 A * heapA = new A（）; 
 

现在你有一个指向A的指针，只要你需要它就可以使用它。

之后你需要销毁它才能释放内存：

 delete heapA; 
 

我希望能回答你的问题。有关详细信息，请参阅内存分配策略 - ModernesCpp.com [ ^

Let's say we have a class A

class A 
{
// blabla
public int x;
}

when we do this:

A a=new A();

is the x also allocated dynamically?
An explanation will be great. Thank you

What I have tried:

I think it is done dynamically since we need to go threw the object to access "x".

解决方案

Only the non-static member variables are stored within the allocated memory block. With your example the memory holds only the x member and has therefore at least the size of an int.

You can verify this by printing out the addresses:

class A
{
public:
    A() { x = 0; }
    int x;
};

int main()
{
    A *a = new A();
    printf("Size of A = %lu\n", sizeof(*a));
    printf("Address of a = %p\n", a);
    printf("Address of a->x = %p\n", &a->x);
    return 0;
}

which might print

Size of A = 4
Address of a = 0x602010
Address of a->x = 0x602010

Note also the correct syntax used in my example (class definition must be terminated with a semicolon and a is a pointer).

You can create object on the stack or dynamically on the heap.
On the stack:

void myFunc()
{
   A a;
}

Now exists the "a" as long as you execute the myFunc.

Dynamically on heap:

A* heapA = new A();

Now you have a pointer to A and can use it as long as you need it.
After that you need to destroy it in order to get the memory free:

delete heapA;

I hope that answers your question. For more details take a look at Strategies for the Allocation of Memory - ModernesCpp.com[^]

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