元素為指針的vector的使用說明

該程序演示了vector中的元素為指針的時候的對對象的操作。

/*
功能說明：
    元素為指針的vector的使用說明
實現方式：
    使用this成員來顯示各個對象的地址。
限制條件或者存在的問題：
    無
*/
#include <iostream>
#include <string>
#include <vector>

using namespace std;

class CData
{
public:
    CData()
    {
        sequence = 0;
        this->remark = "default string";

        cout << "CData()\t" << toString() <<"\t"<< this << endl;
    }

    CData(int i,string &s)
    {
        this->sequence = i;
        this->remark = s;

        cout << "CData(int i,string &s)\t" << toString() << "\t" << this << endl;
    }

    void setSequence(const int i)
    {
        this->sequence = i;
    }

    void setRemark(const string &s)
    {
        this->remark = s;
    }

    string toString() const
    {
        char tmp[2048] = { 0 };
        sprintf(tmp, "[sequence:%d | remark:%s]", this->sequence, this->remark.c_str());

        //此處應該有內存復制操作，所以不用擔心返回后tmp數組所指向的內存被修改或者不存在的情況。
        return tmp;
    }

    ~CData()
    {
        cout << "~CData()\t" << this << endl;
    }
protected:
private:
    int sequence;
    string remark;
};

int main(int argc, char **argv)
{
    cout << "process begin at " << (void*)&main << endl;

    string str = "baby test";
    // 查看保存在系統的棧中的對象的地址。
    cout << "==========test class object in stack" << endl;
    CData data1;
    cout << "address of object in stack:" << &data1 << "\tdefalut object elements:" << data1.toString() << endl;
    data1.setSequence(11);
    data1.setRemark(str);
    cout << "address of object in stack:" << &data1 << "\tafter set object elements:" << data1.toString() << endl;

    // 查看保存在系統的堆中的對象的地址。這種對象需要手工刪除，否則會造成內存泄露
    cout << "\n==========test class object in heap" << endl;
    CData *p_data12 = new CData(12, str); // 帶有參數的構造函數的第二個參數為一個地址，所以，此處的調用必須為一個對象。不能是一個字符數組。
    cout << "address of pointer of class object in stack:" << &p_data12 << "\taddress of class object in heap:" << p_data12 << "\tobject in heap:" << p_data12->toString() << endl;

    CData *p_data13 = new CData(13, str);
    cout << "address of pointer of class object in stack:" << &p_data13 << "\taddress of class object in heap:" << p_data13 << "\tobject in heap:" << p_data13->toString() << endl;

    cout << "\n==========vector test. object in heap" << endl;
    vector<CData*> vec_data;
    vec_data.push_back(p_data12);
    vec_data.push_back(p_data13);
    vec_data.push_back(p_data12);
    vec_data.push_back(p_data13);
    // 上述操作完成之后，堆中有2個對象，但是，這兩個對象分別有3個指針來指向他。一個是原始的創建對象的時候的。另外兩個是上面的push_back所復制的。
    cout << "show vector's msg" << endl;
    for (int i = 0; i < vec_data.size(); i++)
    {
        // 查看vector元素的地址，說明，vector中的元素的位置是連續的。
        cout << "address of element in vector:" << &(vec_data[i]) << endl;
        CData *pTmp = vec_data[i];
        cout << "object address in heap:" << pTmp << "\tobject msg in heap:" << (pTmp)->toString() << endl;
    }

    vec_data.clear();
    // 清理掉vector中的元素。也僅是清理掉vector中的指向對象的指針，並沒有清理掉這些指針所指向的對象。另外，其原始的指向對象的指針還是存在的。
    cout << "\n==========check objects in heap after clear vector" << endl;
    cout << "address of class object in heap:" << p_data12 << "\tobject in heap:" << p_data12->toString() << endl;
    cout << "address of class object in heap:" << p_data13 << "\tobject in heap:" << p_data13->toString() << endl;

    cout << "\n==========delete object in heap using vector iterator" << endl;
    // 再將兩個對象的指針復制到vector中。
    vec_data.push_back(p_data12);
    vec_data.push_back(p_data13);
    for (vector<CData*>::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
    {
        // 通過迭代器來刪除每個指針指向的對象。如果vector中的多個元素指向了同一個對象（上面的情形），此處的程序會異常退出。
        cout <<"delete object:" << *itr << endl;
        delete *itr;
        *itr = 0;
    }

    // 清理vector元素中的指針所指向的對象。並不意味着去清理了vector本身，所以，其長度還是原來的數值。
    cout << "vector length is " << vec_data.size() << endl;
    cout << "\n==========check objects in heap using vector after delete objects" << endl;
    for (vector<CData*>::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
    {
        // vecotr中的指針已經在上面被修改，這里是查看一下。
        cout << "address of object in heap:" << *itr << endl;
    }

    vec_data.clear();

    cout << "\n==========check objects in heap using original pointer after delete objects" << endl;
    // 上面的vector中，已經刪除的堆中的對象。所以下面的對象的toString()操作將是錯誤的。使用此函數，會導致程序異常退出。
    //cout << "address of class object in heap:" << p_data12 << "\tobject in heap:" << p_data12->toString() << endl;
    //cout << "address of class object in heap:" << p_data13 << "\tobject in heap:" << p_data13->toString() << endl;
    
    // 上面的vector中，已經刪除了堆中的對象。但是原始的指向對象的指針還是存在的，只不過是其指向的內存已經無效。
    cout << "address of class object in heap:" << p_data12 << endl;
    cout << "address of class object in heap:" << p_data13 << endl;

    // 此處相當於去刪除一個無效的堆的對象，會導致程序異常退出。
    //delete p_data12;
    //delete p_data13;

    // 其所指向的對象已經在vector中刪除，所以需要將其指向的地址清理掉，防止錯誤。
    p_data12 = 0;
    p_data13 = 0;

    cout << "process end " << (void*)&main << endl;
    
    // 程序退出前，會自動清理掉棧中的對象。

    return 0;
}

程序的輸出結果：

process begin at 002D170D
==========test class object in stack
CData() [sequence:0 | remark:default string]    008FF9D8
address of object in stack:008FF9D8     defalut object elements:[sequence:0 | remark:default string]
address of object in stack:008FF9D8     after set object elements:[sequence:11 | remark:baby test]

==========test class object in heap
CData(int i,string &s)  [sequence:12 | remark:baby test]        00906BB8
address of pointer of class object in stack:008FF9CC    address of class object in heap:00906BB8        object in heap:[sequence:12 | remark:baby test]
CData(int i,string &s)  [sequence:13 | remark:baby test]        00902F30
address of pointer of class object in stack:008FF9C0    address of class object in heap:00902F30        object in heap:[sequence:13 | remark:baby test]

==========vector test. object in heap
show vector's msg
address of element in vector:0090B8E8
object address in heap:00906BB8 object msg in heap:[sequence:12 | remark:baby test]
address of element in vector:0090B8EC
object address in heap:00902F30 object msg in heap:[sequence:13 | remark:baby test]
address of element in vector:0090B8F0
object address in heap:00906BB8 object msg in heap:[sequence:12 | remark:baby test]
address of element in vector:0090B8F4
object address in heap:00902F30 object msg in heap:[sequence:13 | remark:baby test]

==========check objects in heap after clear vector
address of class object in heap:00906BB8        object in heap:[sequence:12 | remark:baby test]
address of class object in heap:00902F30        object in heap:[sequence:13 | remark:baby test]

==========delete object in heap using vector iterator
delete object:00906BB8
~CData()        00906BB8
delete object:00902F30
~CData()        00902F30
vector length is 2

==========check objects in heap using vector after delete objects
address of object in heap:00000000
address of object in heap:00000000

==========check objects in heap using original pointer after delete objects
address of class object in heap:00906BB8
address of class object in heap:00902F30
process end 002D170D
~CData()        008FF9D8