C++ 传递对象地址时“地址表达式必须是左值或函数指示符”
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原文地址: http://stackoverflow.com/questions/10516554/
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"Address expression must be an lvalue or a function designator" when passing an object's address
提问by Reck Hou
Here is part of my code:
这是我的代码的一部分：
class A
{
public:
void init(classB& pObject);
classB& _pObject;
}
void classA::init(classB& pObject)
{
_pObject = pObject;
}
class B
{
public:
void init();
}
void classB::init()
{
classA* pClassA = new classA;
pClassA->init(&this);
}
I got 2 problems after compile:
编译后我遇到了两个问题：
_pObject = pObject;: No viable overloaded '='pClassA->init(&this);: Address expression must be an lvalue or a function designator
_pObject = pObject;: 没有可行的重载 '='pClassA->init(&this);: 地址表达式必须是左值或函数指示符
I'm getting confused about these problems... How can I fix that?
我对这些问题感到困惑......我该如何解决？
采纳答案by Gorpik
First, there is a typo in the question. I assume that Aand classArefer to the same class, ditto for Band classB.
首先，问题中有一个错字。我假设A并classA指的是同一个类，同理B和classB。
1) One of the few differences between a reference and a pointer is that you cannot assign a different value to a reference once it's been initialised. So you just cannot assign to _pObject, though you can initialise it in the initialisation list of the constructor for class A:
1) 引用和指针之间的少数区别之一是，一旦引用被初始化，就不能为其分配不同的值。所以你不能分配给_pObject，尽管你可以在类的构造函数的初始化列表中初始化它A：
classA::classA(classB& object) : _pObject(object) // Correct
{
// _pObject = object; on the other hand, this would be incorrect
}
2) &thisis the address of this, but you actually want a reference to the value pointed to by this. You need to use *thisinstead. Though we have already seen that there is no way to make function classA::initwork with your current class design. If you really want to change the value of _pObjectafter the object has been constructed, you need to make it a classB*instead of a classB&.
2)&this是 的地址this，但您实际上想要对 指向的值的引用this。你需要*this改用。尽管我们已经看到没有办法让函数classA::init与您当前的类设计一起工作。如果您真的想_pObject在对象被构造后更改 的值，则需要将其设为 aclassB*而不是 a classB&。
回答by Alexander Poluektov
1) You should use *thisin this context, as &thishas the type of ClassB**, not ClassB&;
1) 您应该*this在此上下文中使用,&this的类型ClassB**，而不是ClassB&;
2) You can only initialize you reference member-variables in constructor:
2）您只能在构造函数中初始化您引用的成员变量：
classA::classA(classB& b) : _pObject(b)
{
}
(BTW I suppose that you ommitted deletestatement just for brevity)
（顺便说一句，我想您delete只是为了简洁而省略了陈述）
