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[英]How does the linker handle identical template instantiations across translation units?
[英]Why does declaring runtime polymorphism for template instantiations result in linker error?
我有一个完美的工作代码:
template <typename ...Ts>
class ThreadImplementation {
...
void launch(){...}
~ThreadImplementation(){...}
};
...
ThreadImplementation<Ts...> *t = new ThreadImplementation<Ts...>(debugName,func,args...);
...
// std::vector< std::unique_ptr< ThreadImplementation<> > > thread_107_allThreads;
thread_107_allThreads.emplace_back(t);
...
其中,thread_107_allThreads截至目前仅存储没有模板参数的线程,因此在声明中使用ThreadImplementation <>
现在,如果我首先添加
class AnyThreadImplementation {
public:
virtual void launch() = 0;
virtual ~AnyThreadImplementation() = 0;
};
并仅进行以下3项更改(不进行强制转换,不更改使用方式也不进行测试):
class ThreadImplementation : public AnyThreadImplementation {
virtual void launch(){...}
virtual ~ThreadImplementation(){...}
(尽管最后两次更改不会影响结果,即:如果我在子类中的实际实现之前错过了虚函数,则会收到相同的错误)
我得到:
/tmp/test-fuPonc.o: In function `_ZN20ThreadImplementationIJEEC2EPKcPFvvE':
test.cpp:(.text._ZN20ThreadImplementationIJEEC2EPKcPFvvE[_ZN20ThreadImplementationIJEEC2EPKcPFvvE]+0xbb): undefined reference to `AnyThreadImplementation::~AnyThreadImplementation()'
/tmp/test-fuPonc.o: In function `_ZN20ThreadImplementationIJEED2Ev':
test.cpp:(.text._ZN20ThreadImplementationIJEED2Ev[_ZN20ThreadImplementationIJEED2Ev]+0x233): undefined reference to `AnyThreadImplementation::~AnyThreadImplementation()'
test.cpp:(.text._ZN20ThreadImplementationIJEED2Ev[_ZN20ThreadImplementationIJEED2Ev]+0x267): undefined reference to `AnyThreadImplementation::~AnyThreadImplementation()'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
为什么呢
也应该定义纯虚拟析构函数。
N3376 12.4 / 9的相关报价
析构函数可以声明为虚拟或纯虚拟; 如果在程序中创建了该类的任何对象或任何派生类,则应定义析构函数。
class AnyThreadImplementation {
public:
virtual void launch() = 0;
virtual ~AnyThreadImplementation() = 0;
};
AnyThreadImplementation::~AnyThreadImplementation() {}
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