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
This is definitely not a nasty hack, but be aware of the fact that you will have to do it (the explicit template specialization) for every class/type you want to use with the given template. In case of MANY types requesting template instantiation there can be A LOT of lines in your .cpp file. To remedy this problem you can have a TemplateClassInst.cpp in every project you use so that you have greater control what types will be instantiated. Obviously this solution will not be perfect (aka silver bullet) as you might end up breaking the ODR :).
其他回答
对于本页上的其他人来说，想知道显式模板专门化(至少在VS2008中)的正确语法是什么(和我一样)，它如下…
在你的.h文件中…
template<typename T>
class foo
{
public:
void bar(const T &t);
};
在你的。cpp文件中
template <class T>
void foo<T>::bar(const T &t)
{ }
// Explicit template instantiation
template class foo<int>;
你举的例子没有问题。但是我必须说，我认为在cpp文件中存储函数定义是不有效的。我只理解需要将函数的声明和定义分开。
当与显式类实例化一起使用时，Boost Concept Check Library (BCCL)可以帮助您在cpp文件中生成模板函数代码。
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。
在最新的标准中，有一个关键字(export)可以帮助缓解这个问题，但在我所知道的任何编译器中都没有实现，除了Comeau。
请参阅FAQ-lite。
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。
