C++模板的應用

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需求：類比數組類，只不過數群組類型不再是整型、浮點型等，也可以是類。

1、建立模板類

標頭檔

#ifndef MYVECTOR_H#define MYVECTOR_H#include <iostream>#include"Teacher.h"using namespace std;template <typename T>class myVector{public:    myVector();    void init(int size=0);   //建構函式    myVector(const myVector &obj);  //拷貝建構函式    ~myVector();    //解構函式    const int getLen() const;    const T* getSpace() const {return m_space;}    T& operator [](int index);    myVector<T> &operator =(const myVector<T> &obj);private:    T *m_space;    int m_len;};#endif // MYVECTOR_H

 資源檔

#include "myvector.h"#include"Teacher.h"template<typename T>myVector<T>::myVector(){    m_space = NULL;    m_len = 0;}template<typename T>void myVector<T>::init(int size){    m_space=new T[size];    this->m_len=size;}template<typename T>myVector<T>::myVector(const myVector &obj)  //拷貝建構函式{    m_len=obj.m_len;    cout<<m_len<<endl;    m_space=new T[m_len];    for (int i = 0; i < m_len; ++i) {        m_space[i]=obj.m_space[i];    }}template<typename T>myVector<T>::~myVector()    //解構函式{    cout<<"destory....."<<endl;    if(m_space != NULL){        delete [] m_space;        m_space=NULL;        m_len=0;    }}template<typename T>const int myVector<T>::getLen() const{    return m_len;}template<typename T>T& myVector<T>::operator [](int index){    return m_space[index];}template<typename T>myVector<T> & myVector<T>::operator= (const myVector<T> &obj){    //先釋放舊的記憶體    if(m_space != NULL){        cout<<"not null"<<endl;        delete[] m_space;        m_space=NULL;        m_len=0;    }    //根據參數分配記憶體    int length = obj.getLen();    m_space=new T[length];    this->m_len=length;    for (int i = 0; i < m_len; ++i) {        m_space[i]=obj.getSpace()[i];    }    return *this;}

 2、實驗類

標頭檔

#ifndef TEACHER_H#define TEACHER_H#include<iostream>using namespace std;class Teacher{public:    Teacher();    Teacher(char *name,int age);    Teacher(const Teacher &teacher);    ~Teacher();    void printTeacher();    friend ostream &operator <<(ostream &out,Teacher &teacher);    Teacher &operator =(const Teacher &teacher);private:    int age;    char *name;};#endif // TEACHER_H

資源檔

#include "Teacher.h"#include<iostream>#include<string.h>using namespace std;Teacher::Teacher(){    age=0;    name=new char[1];    strcpy(name," ");}Teacher::Teacher(char *name, int age){    this->name=new char[strlen(name)];    strcpy(this->name,name);    this->age=age;}Teacher::Teacher(const Teacher &teacher){    this->name=new char[strlen(teacher.name)];    strcpy(this->name,teacher.name);    this->age=age;}Teacher::~Teacher(){    if(this->name!=NULL){        delete[] this->name;        this->name=NULL;        age==0;    }}void Teacher::printTeacher(){    cout<<"Teacher( name: "<<this->name<<" age: "<<this->age<<" )"<<endl;}ostream &operator <<(ostream &out,Teacher &teacher){    out<<"Teacher( name: "<<teacher.name<<" age: "<<teacher.age<<" )"<<endl;    return out;}Teacher & Teacher::operator =(const Teacher &teacher){    if (this->name != NULL) {        delete[] this->name;        this->name=NULL;    }    this->name=new char[strlen(teacher.name)];    strcpy(this->name,teacher.name);    this->age=teacher.age;    return *this;}

 3、測試函數

主函數

#include "myvector.cpp"#include"Teacher.h"int main(){    myVector<int> myv;    myv.init(10);    for (int i = 0; i < myv.getLen(); ++i) {        myv[i] = i+1;        cout<<myv[i]<<" ";    }    cout<<endl;    myVector<int> myv2=myv;    for (int i = 0; i < myv2.getLen(); ++i) {        cout<<myv2[i]<<" ";    }    cout<<endl;    myVector<int> myv3;    myv3=myv;    for (int i = 0; i < myv3.getLen(); ++i) {        cout<<myv3[i]<<" ";    }    Teacher t1("ggg",22),t2("qqq",23),t3("xxx",24);    myVector<Teacher> t;    t.init(3);    t[0]=t1;    t[1]=t2;    t[2]=t3;    cout<<endl;    for (int i = 0; i < 3; ++i) {        cout<<t[i];    }    return 0;}

 注意事項：

　　在主函數中加入了

#include "myvector.cpp"

問題的根源在於編譯器對於模板(template)的編譯處理過程中，

大致是這樣的(果真如此嗎？)：

1、模板myVector在編譯(compile)期間並未產生具體二進位代碼，

    在main函數中也沒有嵌入這個函數的代碼，可能只是包含了一句

    call testFunc之類的(稍後詳述)

2、編譯階段，在main函數中發現了myVector的引用，但是main.obj中沒有相關的

     可執行代碼（編譯器認為該函數在別處定義，這就是為什麼需要連結也就是

     LINK了，在main中雖然引用到myVector但是只提供了一個call虛擬位址而沒有

     實際的執行代碼）

3、連結階段，將各個模組(編譯期間產生的很多*.obj檔案)組織起來

     形象的說就是，在LINK的時候把testFunc“嵌入”進來，就像是一個子過程，

     在main中從調用處jump到這裡即可，執行完畢再跳出子模組，從“中斷點”

     繼續執行後續語句）

4、模板在編譯期間是不產生具體代碼的。

C++模板的應用