STL container as a template parameter

stl的container都是模板类，如何将它们作为template parameter呢？这是本节探讨的一个话题。

stackoverflow STL container as a template parameter

I'm trying to pass an STL container as a template parameter. In this case, the vector.

Here is my not-functional code:

template<template<class> class TContainer, class TObject>
class Foobar
{
public:

    explicit Foobar( TContainer<TObject*> & container )
    :
    container_( container ){}


private:

    TContainer<TObject*> & container_;
};


int _tmain(int argc, _TCHAR* argv[])
{
    std::vector<IUnknown*> v;

    Foobar<std::vector, IUnknown*> bla( v );

    return 0;
}

Is this, what I'm trying to do possible at all, because the compiler cannot swallow this?

A

There are several things wrong with your code, here is a working example:

template<template<class, class> class TContainer, class TObject>
class Foobar
{
public:
    explicit Foobar( TContainer<TObject*, std::allocator<TObject*>> & container )
    :
    container_( container ){}

private:
    TContainer<TObject*, std::allocator<TObject*>> & container_;
};

int main()
{
    std::vector<IUnknown*> v;
    Foobar<std::vector, IUnknown> bla( v );
}

The main fault of your codes it that std::vector takes two template arguments. It looks like this template<class T, class Allocator = std::allocator<T>> class vector;. Also, Joachim Pileborg is right about the double pointer issue, IUnknown**. However, you could simplify your code with the following:

template<class TContainer>
class Foobar
{
public:
    explicit Foobar( TContainer & container )
    :
    container_( container ){}

private:
    TContainer & container_; // Be careful with reference members
};

int main()
{
    std::vector<IUnknown*> v;
    Foobar<std::vector<IUnknown*>> bla( v ); // C++11 decltype(v) could be used
}

libstdc++ std::stack

libstdc++ std::stack 的实现是非常值得借鉴的:

template<typename _Tp, typename _Sequence = deque<_Tp> >
class stack
{


};

需要注意的是， 它的第二个模板参数_Sequence不是template template parameter，而是一个普通的type template parameter。

下面是std::stack的一些例子：

std::stack<int> stack1;
stack1.push(5);

std::stack<double, std::vector<double>> stack2;
stack2.push(10.5);

Type template parameter _Sequence VS template template parameter Cont

modernescpp Types-, Non-Types, and Templates as Template Parameters 中 class Matrix的第二个template parameter Cont是一个template template parameter，所以它的argument可以是std::vector（需要注意的是std::vector是一个template class，而不是一个class）；所以它的instantiation如下：

Matrix<int, std::vector> myIntVec{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; 

libstdc++ std::stack 的_Sequence是type template parameter，所以它的argument不能够是template，而只能够是type；所以它的instantiation如下：

std::stack<double, std::vector<double>> stack2;

Application

Generic container printer

1、stackoverflow What are some uses of template template parameters? # A

TODO

http://www.cs.technion.ac.il/users/yechiel/c++-faq/template-of-template.html

我的实践

将一个模板类作为一个目标类的成员变量：

template<class T>
class T1
{};

template<class T>
class T2
{
T1<T> t;
};

int main()
{
T1<int> t1;
T2<int> t2;

}

将一个模板类作为参数:

template<class T>
class T1
{};

template<template<class> class argument>
class T2
{};

int main()
{
T1<int> t1;
T2<T1> t2;

}

template<typename FieldT>
struct CUstOptOrderInfoBase
{

    HSIssuetype Issuetype;

    HSNum SequenceNumber;

    FieldT RspQryOrder;
};

template<template<typename > typename InfoT, typename FieldT>
struct CUstOptOrderRspBase
{
    MSG_HEAD MsgHead;
    SBusinessNotifyHead NotifyHead;
    STradeNotifyKey TradeNotifyKey;
    InfoT<FieldT> RtnMsgRsp;
};

// 行权
using CUstOptExerciseInfo = CUstOptExerciseInfoBase<CHSInsRspQryExerciseField>;
using CUstOptExerciseRsp = CUstOptExerciseRspBase<CUstOptExerciseInfoBase, CHSInsRspQryExerciseField>;