元素为指针的vector的使用说明

该程序演示了vector中的元素为指针的时候的对对象的操作。

/*
功能说明：
    元素为指针的vector的使用说明
实现方式：
    使用this成员来显示各个对象的地址。
限制条件或者存在的问题：
    无
*/
#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());

        //此处应该有内存复制操作，所以不用担心返回后tmp数组所指向的内存被修改或者不存在的情况。
        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";
    // 查看保存在系统的栈中的对象的地址。
    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;

    // 查看保存在系统的堆中的对象的地址。这种对象需要手工删除，否则会造成内存泄露
    cout << "\n==========test class object in heap" << endl;
    CData *p_data12 = new CData(12, str); // 带有参数的构造函数的第二个参数为一个地址，所以，此处的调用必须为一个对象。不能是一个字符数组。
    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个对象，但是，这两个对象分别有3个指针来指向他。一个是原始的创建对象的时候的。另外两个是上面的push_back所复制的。
    cout << "show vector's msg" << endl;
    for (int i = 0; i < vec_data.size(); i++)
    {
        // 查看vector元素的地址，说明，vector中的元素的位置是连续的。
        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。也仅是清理掉vector中的指向对象的指针，并没有清理掉这些指针所指向的对象。另外，其原始的指向对象的指针还是存在的。
    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;
    // 再将两个对象的指针复制到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++)
    {
        // 通过迭代器来删除每个指针指向的对象。如果vector中的多个元素指向了同一个对象（上面的情形），此处的程序会异常退出。
        cout <<"delete object:" << *itr << endl;
        delete *itr;
        *itr = 0;
    }

    // 清理vector元素中的指针所指向的对象。并不意味着去清理了vector本身，所以，其长度还是原来的数值。
    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中的指针已经在上面被修改，这里是查看一下。
        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，已经删除的堆中的对象。所以下面的对象的toString()操作将是错误的。使用此函数，会导致程序异常退出。
    //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，已经删除了堆中的对象。但是原始的指向对象的指针还是存在的，只不过是其指向的内存已经无效。
    cout << "address of class object in heap:" << p_data12 << endl;
    cout << "address of class object in heap:" << p_data13 << endl;

    // 此处相当于去删除一个无效的堆的对象，会导致程序异常退出。
    //delete p_data12;
    //delete p_data13;

    // 其所指向的对象已经在vector中删除，所以需要将其指向的地址清理掉，防止错误。
    p_data12 = 0;
    p_data13 = 0;

    cout << "process end " << (void*)&main << endl;
    
    // 程序退出前，会自动清理掉栈中的对象。

    return 0;
}

程序的输出结果：

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