模板类：没有默认构造函数
我知道有一百万篇关于此的帖子，但我仍然不明白为什么这不起作用=/
这一行：
test = new Test2<Test>;
给了我这个错误：
error C2512: 'Test2<PARENT>' : no appropriate default constructor available
with
[
PARENT=Test
]
代码：
template<class PARENT>
class Test2;
////////////////////////////
class Test
{
public:
Test2<Test> *test;
Test()
{
test = new Test2<Test>;
}
};
/////////////////////////////
template<class PARENT>
class Test2
{
public:
PARENT *parent;
};
////////////////////////////
有人可以帮助我吗？
I know there are a million posts about this, but I still can't figure out why this isn't working =/
this line:
test = new Test2<Test>;
gives me this error:
error C2512: 'Test2<PARENT>' : no appropriate default constructor available
with
[
PARENT=Test
]
code:
template<class PARENT>
class Test2;
////////////////////////////
class Test
{
public:
Test2<Test> *test;
Test()
{
test = new Test2<Test>;
}
};
/////////////////////////////
template<class PARENT>
class Test2
{
public:
PARENT *parent;
};
////////////////////////////
can someone help me out?
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评论（3）
在实例化点（即在
Test构造函数内），编译器到目前为止所拥有的只是Test2的前向声明；它还不知道有哪些构造函数可用。要解决此问题，请将
Test2<>的定义移动到Test的定义之前，或者移动Test的定义code> 类定义之外的构造函数（以及Test2<>的定义之后）。At the point of instantiation (i.e. inside the
Testconstructor), all the compiler has so far is a forward declaration ofTest2<>; it doesn't yet know what constructors are available.To solve, either move the definition of
Test2<>before that ofTest, or move the definition of theTestconstructor outside the class definition (and after the definition ofTest2<>).对我来说，您的代码给出了（正确地，恕我直言）错误：
This is with g++ 4.5.1。此时您会说：
Test2 尚未定义，仅向前声明。
For me, your code gives (correctly, IMHO) the error:
This is with g++ 4.5.1. At the point you say:
Test2 has not been defined, only forward declared.
test = new Test2; 行在 Test 的默认构造函数内执行。此行将调用不带参数的默认构造函数/构造函数。当调用上述语句时，Test 的构造函数仍然不完整。
The line
test = new Test2<Test>;is executing inside default constructor of Test.And this line will call the default constructor/constructor with no arguments. The constructor of Test is still not complete when the mentioned statement is being called.