c++ template confusions

Question

I am writing some code using template,but i got some link errors:

[Linker error] undefined reference to `Vector::Vector(Vector const&)'

But i wrote this function in a .cpp.Here is the code.

template <class T>

Vector<T>::Vector(Vector const& r)
{


m_nSize = r.size();
int i = 0;
m_pElements = new T[m_nSize];
    while(i <= m_nSize)
{
    m_pElements[i] = r[i];
    i++;
}
}

and it is declared here in .h:

template <class T>

class Vector
{

public:

Vector():m_nSize(0){ m_pElements = (T*)NULL; }
Vector(int size):m_nSize(size){ m_pElements = new T[size]; }
Vector(const Vector& r);
virtual ~Vector(){ delete m_pElements; }
T& operator[](int index){ return m_pElements[index];}
int size(){return m_nSize;}
int inflate(int addSize);
private:

    T *m_pElements;
    int m_nSize;
};

I'm really confused now...What should i do to correct is?

Related question: [Why can templates only be implemented in the header file?](http://stackoverflow.com/q/495021/20984) — Luc Touraille, May 25 '12 at 08:38

score 3 · Answer 1 · answered May 25 '12 at 08:26

3

You should make implementations visible. Move

template <class T>
Vector<T>::Vector(Vector const& r)
{
    //....
}

from the cpp file to the header.

answered May 25 '12 at 08:26

Luchian Grigore

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score 2 · Answer 2 · answered May 25 '12 at 08:27

2

See the C++ faq (http://www.parashift.com/c++-faq-lite/templates.html#faq-35.13). Basically place the code in the header file.

answered May 25 '12 at 08:27

sashang

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Thanks for your help,the linkpage helps me a lot~ – user1416891 May 25 '12 at 09:02

c++ template confusions

2 Answers2