我有一些模板代码，我宁愿存储在一个CPP文件，而不是内联在头。我知道这是可以做到的，只要您知道将使用哪种模板类型。例如:
. h文件
class foo
{
public:
template <typename T>
void do(const T& t);
};
. cpp文件
template <typename T>
void foo::do(const T& t)
{
// Do something with t
}
template void foo::do<int>(const int&);
template void foo::do<std::string>(const std::string&);
注意最后两行- foo::do模板函数只用于int和std::string，所以这些定义意味着应用程序将链接。
我的问题是-这是一个讨厌的黑客或这将与其他编译器/链接器工作吗?目前我只在VS2008中使用这段代码，但我想移植到其他环境中。
当前回答
是的，这是做专门化显式实例化的标准方法。如您所述，您不能用其他类型实例化此模板。
编辑:根据评论进行更正。
其他回答
此代码是格式良好的。您只需注意模板的定义在实例化时是可见的。引用标准§14.7.2.4:
非导出函数模板、非导出成员函数模板或类模板的非导出成员函数或静态数据成员的定义应出现在显式实例化的每个转换单元中。
这应该在支持模板的任何地方都能正常工作。显式模板实例化是c++标准的一部分。
这是定义模板函数的标准方法。我认为有三种定义模板的方法。或者可能是4个。每一种都有利弊。
Define in class definition. I don't like this at all because I think class definitions are strictly for reference and should be easy to read. However it is much less tricky to define templates in class than outside. And not all template declarations are on the same level of complexity. This method also makes the template a true template. Define the template in the same header, but outside of the class. This is my preferred way most of the times. It keeps your class definition tidy, the template remains a true template. It however requires full template naming which can be tricky. Also, your code is available to all. But if you need your code to be inline this is the only way. You can also accomplish this by creating a .INL file at the end of your class definitions. Include the header.h and implementation.CPP into your main.CPP. I think that's how its done. You won't have to prepare any pre instantiations, it will behave like a true template. The problem I have with it is that it is not natural. We don't normally include and expect to include source files. I guess since you included the source file, the template functions can be inlined. This last method, which was the posted way, is defining the templates in a source file, just like number 3; but instead of including the source file, we pre instantiate the templates to ones we will need. I have no problem with this method and it comes in handy sometimes. We have one big code, it cannot benefit from being inlined so just put it in a CPP file. And if we know common instantiations and we can predefine them. This saves us from writing basically the same thing 5, 10 times. This method has the benefit of keeping our code proprietary. But I don't recommend putting tiny, regularly used functions in CPP files. As this will reduce the performance of your library.
注意，我不知道臃肿的obj文件的后果。
是时候更新了!创建内联(。Inl，或可能是任何其他)文件，并简单地复制其中所有的定义。确保将模板添加到每个函数之上(template <typename T，…>)。现在，与在内联文件中包含头文件相反，您可以做相反的事情。在类声明之后包含内联文件(# Include "file.inl")。
我真的不知道为什么没有人提到这一点。我看不出有什么直接的缺点。
是的，这是做专门化显式实例化的标准方法。如您所述，您不能用其他类型实例化此模板。
编辑:根据评论进行更正。
