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。

  1 /*
  2 功能说明：
  3     元素为指针的vector的使用说明
  4 实现方式：
  5     使用this成员来显示各个对象的地址。
  6 限制条件或者存在的问题：
  7     无
  8 */
  9 #include <iostream>
 10 #include <string>
 11 #include <vector>
 12 
 13 using namespace std;
 14 
 15 class CData
 16 {
 17 public:
 18     CData()
 19     {
 20         sequence = 0;
 21         this->remark = "default string";
 22 
 23         cout << "CData()	" << toString() <<"	"<< this << endl;
 24     }
 25 
 26     CData(int i,string &s)
 27     {
 28         this->sequence = i;
 29         this->remark = s;
 30 
 31         cout << "CData(int i,string &s)	" << toString() << "	" << this << endl;
 32     }
 33 
 34     void setSequence(const int i)
 35     {
 36         this->sequence = i;
 37     }
 38 
 39     void setRemark(const string &s)
 40     {
 41         this->remark = s;
 42     }
 43 
 44     string toString() const
 45     {
 46         char tmp[2048] = { 0 };
 47         sprintf(tmp, "[sequence:%d | remark:%s]", this->sequence, this->remark.c_str());
 48 
 49         //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。
 50         return tmp;
 51     }
 52 
 53     ~CData()
 54     {
 55         cout << "~CData()	" << this << endl;
 56     }
 57 protected:
 58 private:
 59     int sequence;
 60     string remark;
 61 };
 62 
 63 int main(int argc, char **argv)
 64 {
 65     cout << "process begin at " << (void*)&main << endl;
 66 
 67     string str = "baby test";
 68     // 查看保存在系统的栈中的对象的地址。
 69     cout << "==========test class object in stack" << endl;
 70     CData data1;
 71     cout << "address of object in stack:" << &data1 << "	defalut object elements:" << data1.toString() << endl;
 72     data1.setSequence(11);
 73     data1.setRemark(str);
 74     cout << "address of object in stack:" << &data1 << "	after set object elements:" << data1.toString() << endl;
 75 
 76     // 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
 77     cout << "
==========test class object in heap" << endl;
 78     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。
 79     cout << "address of pointer of class object in stack:" << &p_data12 << "	address of class object in heap:" << p_data12 << "	object in heap:" << p_data12->toString() << endl;
 80 
 81     CData *p_data13 = new CData(13, str);
 82     cout << "address of pointer of class object in stack:" << &p_data13 << "	address of class object in heap:" << p_data13 << "	object in heap:" << p_data13->toString() << endl;
 83 
 84     cout << "
==========vector test. object in heap" << endl;
 85     vector<CData*> vec_data;
 86     vec_data.push_back(p_data12);
 87     vec_data.push_back(p_data13);
 88     vec_data.push_back(p_data12);
 89     vec_data.push_back(p_data13);
 90     // 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。
 91     cout << "show vector's msg" << endl;
 92     for (int i = 0; i < vec_data.size(); i++)
 93     {
 94         // 查看vector元素的地址，说明，vector中的元素的位置是连续的。
 95         cout << "address of element in vector:" << &(vec_data[i]) << endl;
 96         CData *pTmp = vec_data[i];
 97         cout << "object address in heap:" << pTmp << "	object msg in heap:" << (pTmp)->toString() << endl;
 98     }
 99 
100     vec_data.clear();
101     // 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。
102     cout << "
==========check objects in heap after clear vector" << endl;
103     cout << "address of class object in heap:" << p_data12 << "	object in heap:" << p_data12->toString() << endl;
104     cout << "address of class object in heap:" << p_data13 << "	object in heap:" << p_data13->toString() << endl;
105 
106     cout << "
==========delete object in heap using vector iterator" << endl;
107     // 再将两个对象的指针复制到vector中。
108     vec_data.push_back(p_data12);
109     vec_data.push_back(p_data13);
110     for (vector<CData*>::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
111     {
112         // 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。
113         cout <<"delete object:" << *itr << endl;
114         delete *itr;
115         *itr = 0;
116     }
117 
118     // 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。
119     cout << "vector length is " << vec_data.size() << endl;
120     cout << "
==========check objects in heap using vector after delete objects" << endl;
121     for (vector<CData*>::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
122     {
123         // vecotr中的指针已经在上面被修改，这里是查看一下。
124         cout << "address of object in heap:" << *itr << endl;
125     }
126 
127     vec_data.clear();
128 
129     cout << "
==========check objects in heap using original pointer after delete objects" << endl;
130     // 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。
131     //cout << "address of class object in heap:" << p_data12 << "	object in heap:" << p_data12->toString() << endl;
132     //cout << "address of class object in heap:" << p_data13 << "	object in heap:" << p_data13->toString() << endl;
133     
134     // 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。
135     cout << "address of class object in heap:" << p_data12 << endl;
136     cout << "address of class object in heap:" << p_data13 << endl;
137 
138     // 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。
139     //delete p_data12;
140     //delete p_data13;
141 
142     // 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。
143     p_data12 = 0;
144     p_data13 = 0;
145 
146     cout << "process end " << (void*)&main << endl;
147     
148     // 程序退出前，会自动清理掉栈中的对象。
149 
150     return 0;
151 }

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