vector的内存分配机制分析

其他 2018-06-07 05:17:20 阅读次数: 2

该程序初步演示了我对vector在分配内存的时候的理解。可能有误差，随着理解的改变，改代码可以被修改。

/*
功能说明：
	vector的内存分配机制分析。
代码说明：
	vector所管理的内存地址是连续的。程序在不断的push_back的过程中，如果当前所管理的内存不能装下新的元素的时候，程序会创建更大的地址连续的空间来保存更多的元素。
	这种机制会引起大量的无用的复制和删除操作。如果vector的元素为类结构的时候，他就会有很多临时变量产生。通过复制构造函数和析构函数，可以看到这些操作。
实现方式：
	
限制条件或者存在的问题：
	无
*/
#include <iostream>
#include <string>
#include <vector>

#include <windows.h>

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;
	}

	CData(const CData &data)
	{
		this->sequence = data.sequence;
		this->remark = data.remark;

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

	CData operator = (const CData &data)
	{
		this->sequence = data.sequence;
		this->remark = data.remark;

		cout << "CData operator = (const CData &data)\t" << toString() << "\t" << this << endl;

		return *this;
	}

	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";
	CData data1(1, str);
	CData data2(2, str);
	CData data3(3, str);
	CData data4(4, str);
	CData data5(5, str);
	CData data6(6, str);
	CData data7(7, str);
	CData data8(8, str);
	CData data9(9, str);
	CData data10(10, str);

	cout << "push CData to vector" << endl;
	vector<CData> vec_data;
	cout << "max size of vector<CData> is " << vec_data.max_size() << endl;
	cout << "size of vector<CData> is " << vec_data.size() << endl;
	
	cout << "****************vec_data.push_back(data1)" << endl;
	vec_data.push_back(data1);
	Sleep(2 * vec_data.size());
	
	cout << "****************vec_data.push_back(data2)" << endl;
	vec_data.push_back(data2);
	Sleep(2 * vec_data.size());
	
	cout << "****************vec_data.push_back(data3)" << endl;
	vec_data.push_back(data3);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data4)" << endl;
	vec_data.push_back(data4);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data5)" << endl;
	vec_data.push_back(data5);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data6)" << endl;
	vec_data.push_back(data6);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data7)" << endl;
	vec_data.push_back(data7);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data8)" << endl;
	vec_data.push_back(data8);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data9)" << endl;
	vec_data.push_back(data9);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data10)" << endl;
	vec_data.push_back(data10);
	Sleep(2 * vec_data.size());

	// 程序到此为止，日志显示的比较怪异。
	// 具体来说，就是，将CData对象push到向量中的时候，程序会通过复制构造函数，创建一些临时变量。
	// 创建临时变量的原因分析：这可能与vector的内存分配方式有关。vector所创建的对象的内存的地址是连续的。
	// 当当前的vector所拥有内存不能装入新的元素的时候，程序会创建开辟新的地址连续的空间，并将原来地址中的元素全部复制一份，保存到新的地址中。然后在删除原来的地址中的对象。

	cout << "===============show vector by iterator" << endl;
	for (vector<CData>::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
	{
		// 显示的地址信息，是最后一次push的时候所复制的对象的地址。
		cout << "address of itr is " << &(*itr) << "\tvalue is " << itr->toString() << endl;
	}

	cout << "===============clear vector 1" << endl;
	// vector中的元素不是指针，此处的清理，会调用析构函数。
	vec_data.clear();

	// 根据上面的分析，再次测试。
	// 本次测试是在将元素push到vector中之前，先为vector申请“足够大”的内存。
	vec_data.reserve(20);
	cout << "size of vector<CData> is " << vec_data.size() << endl;
	cout << "capacity of vector<CData> is " << vec_data.capacity() << endl;

	cout << "****************vec_data.push_back(data1)" << endl;
	vec_data.push_back(data1);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data2)" << endl;
	vec_data.push_back(data2);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data3)" << endl;
	vec_data.push_back(data3);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data4)" << endl;
	vec_data.push_back(data4);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data5)" << endl;
	vec_data.push_back(data5);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data6)" << endl;
	vec_data.push_back(data6);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data7)" << endl;
	vec_data.push_back(data7);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data8)" << endl;
	vec_data.push_back(data8);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data9)" << endl;
	vec_data.push_back(data9);
	Sleep(2 * vec_data.size());

	cout << "****************vec_data.push_back(data10)" << endl;
	vec_data.push_back(data10);
	Sleep(2 * vec_data.size());

	cout << "===============show vector by iterator 2" << endl;
	for (vector<CData>::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
	{
		cout << "address of itr is " << &(*itr) << "\tvalue is " << itr->toString() << endl;
	}

	// 上面的日志信息显示。vector开始已经有了足够大的地址空间来保存这10个变量，所以，他就不会再频繁创建新的内存地址和创建新对象了。
	// 这样的方式，可以节省很多的系统开销。

	cout << "===============clear vector 2" << endl;
	// vector中的元素不是指针，此处的清理，会调用析构函数。
	vec_data.clear();

	cout << "======================end of process" << endl;

	return 0;
}

程序的结果：
process begin at 00D1173A
CData(int i,string &s)  [sequence:1 | remark:baby_test] 00CAFAD0
CData(int i,string &s)  [sequence:2 | remark:baby_test] 00CAFAA8
CData(int i,string &s)  [sequence:3 | remark:baby_test] 00CAFA80
CData(int i,string &s)  [sequence:4 | remark:baby_test] 00CAFA58
CData(int i,string &s)  [sequence:5 | remark:baby_test] 00CAFA30
CData(int i,string &s)  [sequence:6 | remark:baby_test] 00CAFA08
CData(int i,string &s)  [sequence:7 | remark:baby_test] 00CAF9E0
CData(int i,string &s)  [sequence:8 | remark:baby_test] 00CAF9B8
CData(int i,string &s)  [sequence:9 | remark:baby_test] 00CAF990
CData(int i,string &s)  [sequence:10 | remark:baby_test]        00CAF968
push CData to vector
max size of vector<CData> is 134217727
size of vector<CData> is 0
****************vec_data.push_back(data1)
CData(const CData &data)        [sequence:1 | remark:baby_test] 010485A8
****************vec_data.push_back(data2)
CData(const CData &data)        [sequence:1 | remark:baby_test] 01046F60
~CData()        010485A8
CData(const CData &data)        [sequence:2 | remark:baby_test] 01046F80
****************vec_data.push_back(data3)
CData(const CData &data)        [sequence:1 | remark:baby_test] 0104D230
CData(const CData &data)        [sequence:2 | remark:baby_test] 0104D250
~CData()        01046F60
~CData()        01046F80
CData(const CData &data)        [sequence:3 | remark:baby_test] 0104D270
****************vec_data.push_back(data4)
CData(const CData &data)        [sequence:1 | remark:baby_test] 0104D2C0
CData(const CData &data)        [sequence:2 | remark:baby_test] 0104D2E0
CData(const CData &data)        [sequence:3 | remark:baby_test] 0104D300
~CData()        0104D230
~CData()        0104D250
~CData()        0104D270
CData(const CData &data)        [sequence:4 | remark:baby_test] 0104D320
****************vec_data.push_back(data5)
CData(const CData &data)        [sequence:1 | remark:baby_test] 0104E430
CData(const CData &data)        [sequence:2 | remark:baby_test] 0104E450
CData(const CData &data)        [sequence:3 | remark:baby_test] 0104E470
CData(const CData &data)        [sequence:4 | remark:baby_test] 0104E490
~CData()        0104D2C0
~CData()        0104D2E0
~CData()        0104D300
~CData()        0104D320
CData(const CData &data)        [sequence:5 | remark:baby_test] 0104E4B0
****************vec_data.push_back(data6)
CData(const CData &data)        [sequence:6 | remark:baby_test] 0104E4D0
****************vec_data.push_back(data7)
CData(const CData &data)        [sequence:1 | remark:baby_test] 0104D230
CData(const CData &data)        [sequence:2 | remark:baby_test] 0104D250
CData(const CData &data)        [sequence:3 | remark:baby_test] 0104D270
CData(const CData &data)        [sequence:4 | remark:baby_test] 0104D290
CData(const CData &data)        [sequence:5 | remark:baby_test] 0104D2B0
CData(const CData &data)        [sequence:6 | remark:baby_test] 0104D2D0
~CData()        0104E430
~CData()        0104E450
~CData()        0104E470
~CData()        0104E490
~CData()        0104E4B0
~CData()        0104E4D0
CData(const CData &data)        [sequence:7 | remark:baby_test] 0104D2F0
****************vec_data.push_back(data8)
CData(const CData &data)        [sequence:8 | remark:baby_test] 0104D310
****************vec_data.push_back(data9)
CData(const CData &data)        [sequence:9 | remark:baby_test] 0104D330
****************vec_data.push_back(data10)
CData(const CData &data)        [sequence:1 | remark:baby_test] 0104ED28
CData(const CData &data)        [sequence:2 | remark:baby_test] 0104ED48
CData(const CData &data)        [sequence:3 | remark:baby_test] 0104ED68
CData(const CData &data)        [sequence:4 | remark:baby_test] 0104ED88
CData(const CData &data)        [sequence:5 | remark:baby_test] 0104EDA8
CData(const CData &data)        [sequence:6 | remark:baby_test] 0104EDC8
CData(const CData &data)        [sequence:7 | remark:baby_test] 0104EDE8
CData(const CData &data)        [sequence:8 | remark:baby_test] 0104EE08
CData(const CData &data)        [sequence:9 | remark:baby_test] 0104EE28
~CData()        0104D230
~CData()        0104D250
~CData()        0104D270
~CData()        0104D290
~CData()        0104D2B0
~CData()        0104D2D0
~CData()        0104D2F0
~CData()        0104D310
~CData()        0104D330
CData(const CData &data)        [sequence:10 | remark:baby_test]        0104EE48
===============show vector by iterator
address of itr is 0104ED28      value is [sequence:1 | remark:baby_test]
address of itr is 0104ED48      value is [sequence:2 | remark:baby_test]
address of itr is 0104ED68      value is [sequence:3 | remark:baby_test]
address of itr is 0104ED88      value is [sequence:4 | remark:baby_test]
address of itr is 0104EDA8      value is [sequence:5 | remark:baby_test]
address of itr is 0104EDC8      value is [sequence:6 | remark:baby_test]
address of itr is 0104EDE8      value is [sequence:7 | remark:baby_test]
address of itr is 0104EE08      value is [sequence:8 | remark:baby_test]
address of itr is 0104EE28      value is [sequence:9 | remark:baby_test]
address of itr is 0104EE48      value is [sequence:10 | remark:baby_test]
===============clear vector 1
~CData()        0104ED28
~CData()        0104ED48
~CData()        0104ED68
~CData()        0104ED88
~CData()        0104EDA8
~CData()        0104EDC8
~CData()        0104EDE8
~CData()        0104EE08
~CData()        0104EE28
~CData()        0104EE48
size of vector<CData> is 0
capacity of vector<CData> is 20
****************vec_data.push_back(data1)
CData(const CData &data)        [sequence:1 | remark:baby_test] 0104EEF8
****************vec_data.push_back(data2)
CData(const CData &data)        [sequence:2 | remark:baby_test] 0104EF18
****************vec_data.push_back(data3)
CData(const CData &data)        [sequence:3 | remark:baby_test] 0104EF38
****************vec_data.push_back(data4)
CData(const CData &data)        [sequence:4 | remark:baby_test] 0104EF58
****************vec_data.push_back(data5)
CData(const CData &data)        [sequence:5 | remark:baby_test] 0104EF78
****************vec_data.push_back(data6)
CData(const CData &data)        [sequence:6 | remark:baby_test] 0104EF98
****************vec_data.push_back(data7)
CData(const CData &data)        [sequence:7 | remark:baby_test] 0104EFB8
****************vec_data.push_back(data8)
CData(const CData &data)        [sequence:8 | remark:baby_test] 0104EFD8
****************vec_data.push_back(data9)
CData(const CData &data)        [sequence:9 | remark:baby_test] 0104EFF8
****************vec_data.push_back(data10)
CData(const CData &data)        [sequence:10 | remark:baby_test]        0104F018
===============show vector by iterator 2
address of itr is 0104EEF8      value is [sequence:1 | remark:baby_test]
address of itr is 0104EF18      value is [sequence:2 | remark:baby_test]
address of itr is 0104EF38      value is [sequence:3 | remark:baby_test]
address of itr is 0104EF58      value is [sequence:4 | remark:baby_test]
address of itr is 0104EF78      value is [sequence:5 | remark:baby_test]
address of itr is 0104EF98      value is [sequence:6 | remark:baby_test]
address of itr is 0104EFB8      value is [sequence:7 | remark:baby_test]
address of itr is 0104EFD8      value is [sequence:8 | remark:baby_test]
address of itr is 0104EFF8      value is [sequence:9 | remark:baby_test]
address of itr is 0104F018      value is [sequence:10 | remark:baby_test]
===============clear vector 2
~CData()        0104EEF8
~CData()        0104EF18
~CData()        0104EF38
~CData()        0104EF58
~CData()        0104EF78
~CData()        0104EF98
~CData()        0104EFB8
~CData()        0104EFD8
~CData()        0104EFF8
~CData()        0104F018
======================end of process
~CData()        00CAF968
~CData()        00CAF990
~CData()        00CAF9B8
~CData()        00CAF9E0
~CData()        00CAFA08
~CData()        00CAFA30
~CData()        00CAFA58
~CData()        00CAFA80
~CData()        00CAFAA8
~CData()        00CAFAD0

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