今天用類模型實現一個linklist，開始是.h和.cpp將類模板的宣告與實現分開寫的，結果總是報錯：

擺弄了半個小時都不知道為啥，結果一百度，原來類模板的宣告與實現是不能夠分開寫的。

《C++程式設計思想》第15章(第300頁)說明了原因：
模板定義很特殊。由template<…> 處理的任何東西都意味著編譯器在當時不為它分配儲存空間，它一直處於等待狀態直到被一個模板例項告知。在編譯器和聯結器的某一處，有一機制能去掉指定模板的多重定義。所以為了容易使用，幾乎總是在標頭檔案中放置全部的模板宣告和定義。

這裡把我的linklist的程式碼也貼過來好了：

//linklist.h
 

#pragma once
#ifndef _LINKLIST_H_
#define _LINKLIST_H_

#include<iostream>

using namespace std;

template<typename T>
struct Node {
    T t;
    struct Node<T>* next;
};

template<typename T>
class linklist {
public:
    linklist();
    ~linklist();
public:
    int clear();
    int
 
 getlength();
    int getnode(int pos, T &t);
    int insertnode(int pos, T &t);
    int deletenode(int pos, T &t);
private:
    int m_length;
    Node<T>* m_head;
};

template<typename T>
linklist<T>::linklist() {
    m_head = new Node<T>;
    m_head->next = NULL;
    m_length = 0
 
;
}

template<typename T>
linklist<T>::~linklist() {
    Node<T> *temp = NULL;
    while (m_head) {
        temp = m_head->next;
        delete m_head;
        m_head = temp;
    }
}

template<typename T>
int linklist<T>::clear() {
    Node<T> *temp = NULL;
    while (m_head) {
        temp = m_head->next;
        delete m_head;
        m_head = temp;
    }
    m_head = new Node<T>;
    m_head->next = NULL;
    m_length = 0;
    return 0;
}

template<typename T>
int linklist<T>::getlength() {
    return m_length;
}

template<typename T>
int linklist<T>::getnode(int pos, T &t) {
    int ret = 0;
    if (pos < 0 || pos > m_length) {
        ret = 1;
        cout << "func getnode() pos < 0 || pos > m_length err : " << ret << endl;
        return ret;
    }
    Node<T>* current = m_head;
    int i = 0;
    while (i++ < pos)
        current = current->next;
    t = current->next->t;
    return ret;
}

template<typename T>
int linklist<T>::insertnode(int pos, T &t) {
    int ret = 0;
    if (pos < 0 || pos > m_length) {
        ret = 1;
        cout << "func getnode() pos < 0 || pos > m_length err : " << ret << endl;
        return ret;
    }
    Node<T>* current = m_head;
    int i = 0;
    while (i++ < pos)
        current = current->next;
    Node<T>* newnode = new Node<T>;
    newnode->next = NULL;
    newnode->t = t;
    newnode->next = current->next;
    current->next = newnode;
    m_length++;
    return ret;
}

template<typename T>
int linklist<T>::deletenode(int pos, T &t) {
    int ret = 0;
    if (pos < 0 || pos > m_length) {
        ret = 1;
        cout << "func getnode() pos < 0 || pos > m_length err : " << ret << endl;
        return ret;
    }
    Node<T>* current = m_head;
    int i = 0;
    while (i++ < pos)
        current = current->next;
    Node<T>* delnode = current->next;
    t = delnode->t;
    current->next = delnode->next;
    delete delnode;
    m_length--;
    return ret;
}

#endif

//linklist_cpp_test.cpp
#include<iostream>
#include"linklist.h"

using namespace std;

struct Teacher {
    char name[64];
    int age;
};

void foo() {

    Teacher t1, t2, t3;
    Teacher temp;
    t1.age = 31;
    t2.age = 32;
    t3.age = 33;
    linklist<Teacher> list;
    list.insertnode(0, t1);
    list.insertnode(0, t2);
    list.insertnode(0, t3);

    for (int i = 0; i < list.getlength(); i++) {
        list.getnode(i, temp);
        cout << "temp.age = " << temp.age << endl;
    }

    while (list.getlength() > 0) {
        list.deletenode(0, temp);
        cout << "temp.age = " << temp.age << endl;
    }

}

int main() {
    foo();
    system("pause");
    return 0;
}