仅C ++模板类的实现

Question

I do not have access to c++11 for this project.

I have a C++ class; lets call it Bar, it looks something like this:

Header FooBar.h:

#include "Fancy.h" // <--- Dependency
namespace Foo
{
    template<typename T>
    class Bar : public Fancy::FancyClass<T, ALLOCATER<HARD_CODED_VALUE>>
    {
    };
}

Cpp:

None

Fancy is a lib that is being statically linked into a dll. The problem is that when other projects want to use the dll they include "FooBar.h" it says that it cannot find "Fancy.h"

Basically I want projects that include the dll to be able to use this class without needing any additional libraries or headers.

My solution was to just put it in a cpp and have no header file. Unfortintly nothing can find it then? I have tried creating a blank header file that did not work either.

I tried to forward declare it in the header but to do that I need the .h to understand what FancyClass is. I have also tried

namespace Fancy
{
    class FancyClass;
    class ALLOCATER;
}

namespace Foo
{
    template<typename T>
    class Bar : public Fancy::FancyClass<T, ALLOCATER<HARD_CODED_VALUE>>;
}

in the header. But that causes many errors.

Answer 1

Short answer, you must include the header in your executable file in order to use the provided library.

Long(er) answer, the compiler needs to know the structure of the class defined in the library.

Imagine that there is a class called MyAwesomeClass that is part of a library you want to use in your executable. The compiler doesn't know anything about that class when you say MyAwesomeClass awesome; . How big is it? What methods can you call on it? Does it inherit from anything?

This information is contained in the header file where the class is declared.

class MyAwesomeClass
{
    private:
        std::string _name;
    public:
        MyAwesomeClass();
        MyAwesomeClass(const std::string& name);
        void print_name();
};

The implementation is defined in the DLL or static library, but when using the type MyAwesomeClass , the compiler needs to know at least its structure. Without including the header, the compiler will complain that it doesn't know what type MyAwesomeClass is (ie. undefined class errors).