該程序演示了vector中的元素爲指針的時候的對對象的操作。
/*
功能說明:
元素爲指針的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());
//此處應該有內存複製操作,所以不用擔心返回後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爲一個地址,所以,此處的調用必須爲一個對象。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);
// 上述操作完成之後,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所複製的。
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複製到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,這裏是查看一下。
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