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how to implement a template class with c++ and export in dll/so
Guide
questions
模板类必须在header中实现，而不能在cpp中实现，否则作为dll调用进行链接的时候回出错。
common solutions(Recommend)
implement template functions in header.
ThreadPool.h
class SHARED_EXPORT ThreadPool {
public:
static ThreadPool* Instance(size_t max_thread_pool_size);
~ThreadPool();
// Add new work item to the pool.
template<class F>
inline void Enqueue(F f)
{
io_service_.post(f);//sync, return immediately
}
void Free();
private:
static std::shared_ptr<ThreadPool> m_pInstance;
bool bfree;
ThreadPool(size_t size);
DISABLE_COPY_AND_ASSIGN(ThreadPool);
boost::thread_group workers_;
boost::asio::io_service io_service_;
boost::asio::io_service::work work_;
};
Seperate from headers
solutions 1
A common solution to this is to write the template declaration in a header file, then implement the class in an implementation file (for example .tpp), and include this implementation file at the end of the header.
Foo.h
template <typename T>
struct Foo
{
void doSomething(T param);
};
#include "Foo.cpp" // here
Foo.cpp
template <typename T>
void Foo<T>::doSomething(T param)
{
//implementation
}
solutions 2
Another solution is to keep the implementation separated, and explicitly instantiate all the template instances you'll need:
Foo.h
// no implementation
template <typename T> struct Foo { ... };
Foo.cpp
#include "Foo.h"
// implementation of Foo's methods
// explicit instantiations
template class Foo<int>;
template class Foo<float>;
// You will only be able to use Foo with int or float
// template void TestClass::templateFunction<int, int>(int, int);
Reference
- why-can-templates-only-be-implemented-in-the-header-file
- separate-c-template-headers-h-and
- Cpp_template_definitions_in_a_cpp_file_instead_of_header
History
- 20191012: created.
Copyright
- Post author: kezunlin
- Post link: https://kezunlin.me/post/4ec4ae49/
- Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 3.0 unless stating additionally.