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。
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- 1 /*
- 2 功能说明:
- 3 vector的内存分配机制分析。
- 4 代码说明:
- 5 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。
- 6 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。
- 7 实现方式:
- 8
- 9 限制条件或者存在的问题:
- 10 无
- 11 */
- 12 #include
- 13 #include <string>
- 14 #include
- 15
- 16 #include
- 17
- 18 using namespace std;
- 19
- 20 class CData
- 21 {
- 22 public:
- 23 CData()
- 24 {
- 25 sequence = 0;
- 26 this->remark = "default string";
- 27
- 28 cout << "CData()\t" << toString() <<"\t"<< this << endl;
- 29 }
- 30
- 31 CData(int i,string &s)
- 32 {
- 33 this->sequence = i;
- 34 this->remark = s;
- 35
- 36 cout << "CData(int i,string &s)\t" << toString() << "\t" << this << endl;
- 37 }
- 38
- 39 CData(const CData &data)
- 40 {
- 41 this->sequence = data.sequence;
- 42 this->remark = data.remark;
- 43
- 44 cout << "CData(const CData &data)\t" << toString() << "\t" << this << endl;
- 45 }
- 46
- 47 CData operator = (const CData &data)
- 48 {
- 49 this->sequence = data.sequence;
- 50 this->remark = data.remark;
- 51
- 52 cout << "CData operator = (const CData &data)\t" << toString() << "\t" << this << endl;
- 53
- 54 return *this;
- 55 }
- 56
- 57 void setSequence(const int i)
- 58 {
- 59 this->sequence = i;
- 60 }
- 61
- 62 void setRemark(const string &s)
- 63 {
- 64 this->remark = s;
- 65 }
- 66
- 67 string toString() const
- 68 {
- 69 char tmp[2048] = { 0 };
- 70 sprintf(tmp, "[sequence:%d | remark:%s]", this->sequence, this->remark.c_str());
- 71
- 72 //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。
- 73 return tmp;
- 74 }
- 75
- 76 ~CData()
- 77 {
- 78 cout << "~CData()\t" << this << endl;
- 79 }
- 80 protected:
- 81 private:
- 82 int sequence;
- 83 string remark;
- 84 };
- 85
- 86 int main(int argc, char **argv)
- 87 {
- 88 cout << "process begin at " << (void*)&main << endl;
- 89
- 90 string str = "baby_test";
- 91 CData data1(1, str);
- 92 CData data2(2, str);
- 93 CData data3(3, str);
- 94 CData data4(4, str);
- 95 CData data5(5, str);
- 96 CData data6(6, str);
- 97 CData data7(7, str);
- 98 CData data8(8, str);
- 99 CData data9(9, str);
- 100 CData data10(10, str);
- 101
- 102 cout << "push CData to vector" << endl;
- 103 vector vec_data;
- 104 cout << "max size of vector<CData> is " << vec_data.max_size() << endl;
- 105 cout << "size of vector<CData> is " << vec_data.size() << endl;
- 106
- 107 cout << "****************vec_data.push_back(data1)" << endl;
- 108 vec_data.push_back(data1);
- 109 Sleep(2 * vec_data.size());
- 110
- 111 cout << "****************vec_data.push_back(data2)" << endl;
- 112 vec_data.push_back(data2);
- 113 Sleep(2 * vec_data.size());
- 114
- 115 cout << "****************vec_data.push_back(data3)" << endl;
- 116 vec_data.push_back(data3);
- 117 Sleep(2 * vec_data.size());
- 118
- 119 cout << "****************vec_data.push_back(data4)" << endl;
- 120 vec_data.push_back(data4);
- 121 Sleep(2 * vec_data.size());
- 122
- 123 cout << "****************vec_data.push_back(data5)" << endl;
- 124 vec_data.push_back(data5);
- 125 Sleep(2 * vec_data.size());
- 126
- 127 cout << "****************vec_data.push_back(data6)" << endl;
- 128 vec_data.push_back(data6);
- 129 Sleep(2 * vec_data.size());
- 130
- 131 cout << "****************vec_data.push_back(data7)" << endl;
- 132 vec_data.push_back(data7);
- 133 Sleep(2 * vec_data.size());
- 134
- 135 cout << "****************vec_data.push_back(data8)" << endl;
- 136 vec_data.push_back(data8);
- 137 Sleep(2 * vec_data.size());
- 138
- 139 cout << "****************vec_data.push_back(data9)" << endl;
- 140 vec_data.push_back(data9);
- 141 Sleep(2 * vec_data.size());
- 142
- 143 cout << "****************vec_data.push_back(data10)" << endl;
- 144 vec_data.push_back(data10);
- 145 Sleep(2 * vec_data.size());
- 146
- 147 // 程序到此为止,日志显示的比较怪异。
- 148 // 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。
- 149 // 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。
- 150 // 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。
- 151
- 152 cout << "===============show vector by iterator" << endl;
- 153 for (vector::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
- 154 {
- 155 // 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。
- 156 cout << "address of itr is " << &(*itr) << "\tvalue is " << itr->toString() << endl;
- 157 }
- 158
- 159 cout << "===============clear vector 1" << endl;
- 160 // vector中的元素不是指针,此处的清理,会调用析构函数。
- 161 vec_data.clear();
- 162
- 163 // 根据上面的分析,再次测试。
- 164 // 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。
- 165 vec_data.reserve(20);
- 166 cout << "size of vector<CData> is " << vec_data.size() << endl;
- 167 cout << "capacity of vector<CData> is " << vec_data.capacity() << endl;
- 168
- 169 cout << "****************vec_data.push_back(data1)" << endl;
- 170 vec_data.push_back(data1);
- 171 Sleep(2 * vec_data.size());
- 172
- 173 cout << "****************vec_data.push_back(data2)" << endl;
- 174 vec_data.push_back(data2);
- 175 Sleep(2 * vec_data.size());
- 176
- 177 cout << "****************vec_data.push_back(data3)" << endl;
- 178 vec_data.push_back(data3);
- 179 Sleep(2 * vec_data.size());
- 180
- 181 cout << "****************vec_data.push_back(data4)" << endl;
- 182 vec_data.push_back(data4);
- 183 Sleep(2 * vec_data.size());
- 184
- 185 cout << "****************vec_data.push_back(data5)" << endl;
- 186 vec_data.push_back(data5);
- 187 Sleep(2 * vec_data.size());
- 188
- 189 cout << "****************vec_data.push_back(data6)" << endl;
- 190 vec_data.push_back(data6);
- 191 Sleep(2 * vec_data.size());
- 192
- 193 cout << "****************vec_data.push_back(data7)" << endl;
- 194 vec_data.push_back(data7);
- 195 Sleep(2 * vec_data.size());
- 196
- 197 cout << "****************vec_data.push_back(data8)" << endl;
- 198 vec_data.push_back(data8);
- 199 Sleep(2 * vec_data.size());
- 200
- 201 cout << "****************vec_data.push_back(data9)" << endl;
- 202 vec_data.push_back(data9);
- 203 Sleep(2 * vec_data.size());
- 204
- 205 cout << "****************vec_data.push_back(data10)" << endl;
- 206 vec_data.push_back(data10);
- 207 Sleep(2 * vec_data.size());
- 208
- 209 cout << "===============show vector by iterator 2" << endl;
- 210 for (vector::iterator itr = vec_data.begin(); itr != vec_data.end(); itr++)
- 211 {
- 212 cout << "address of itr is " << &(*itr) << "\tvalue is " << itr->toString() << endl;
- 213 }
- 214
- 215 // 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。
- 216 // 这样的方式,可以节省很多的系统开销。
- 217
- 218 cout << "===============clear vector 2" << endl;
- 219 // vector中的元素不是指针,此处的清理,会调用析构函数。
- 220 vec_data.clear();
- 221
- 222 cout << "======================end of process" << endl;
- 223
- 224 return 0;
- 225 }
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
size of vector
****************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
capacity of vector
****************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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