C++ 错误：成员访问不完整类型：前向声明
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error: member access into incomplete type : forward declaration of
提问by LOLKFC
I have two classes in the same .cpp file:
我在同一个 .cpp 文件中有两个类：
// forward
class B;
class A?{
void doSomething(B * b) {
b->add();
}
};
class B {
void add() {
...
}
};
The forward does not work, I cannot compile.
转发不起作用，我无法编译。
I get this error:
我收到此错误：
error: member access into incomplete type 'B'
note: forward declaration of 'B'
I'm using clang compiler (clang-500.2.79).
我正在使用 clang 编译器 (clang-500.2.79)。
I don't want to use multiple files (.cpp and .hh), I'd like to code just on one .cpp.
我不想使用多个文件（.cpp 和 .hh），我只想在一个 .cpp 上编码。
I cannot write the class B before the class A.
我不能在 A 类之前写 B 类。
Do you have any idea of how to resolve my problem ?
你知道如何解决我的问题吗？
采纳答案by masoud
Move doSomethingdefinition outside of its class declaration and after Band also make addaccessible to Aby public-ing it or friend-ing it.
将doSomething定义移到其类声明之外和之后，B并通过-ing it 或-ing it使其add可访问。Apublicfriend
class B;
class A
{
void doSomething(B * b);
};
class B
{
public:
void add() {}
};
void A::doSomething(B * b)
{
b->add();
}
回答by Some programmer dude
You must have the definitionof class Bbefore you use the class. How else would the compiler otherwise know that there exists such a function as B::add?
在使用类之前，您必须有类的定义B。否则编译器怎么会知道存在这样的函数B::add？
Either define class Bbefore class A, or move the body of A::doSomethingto after class Bhave been defined, like
要么在 classB之前定义 class ，要么在 class定义之后A移动A::doSomethingto的主体B，例如
class B;
class A
{
B* b;
void doSomething();
};
class B
{
A* a;
void add() {}
};
void A::doSomething()
{
b->add();
}
