cpp: 自定义class中内存管理示例

通过自定义一个String类来表示内存管理在自定义类中需要处理的地方。

//
// Created by cat on 2018/1/2.
//#ifndef CPP02_STRINGBAD_H
#define CPP02_STRINGBAD_Hclass StringBad {private:char *str;unsigned int len;static int nums;static bool DEBUG_LIFESTYLE;static bool DEBUG_OPERATOR;
public:StringBad();StringBad(const char *str);StringBad(const StringBad &obj); // 复制构造virtual ~StringBad();friend std::ostream &operator<<(std::ostream &os, const StringBad &obj);StringBad& operator=(const StringBad &obj);};#endif //CPP02_STRINGBAD_H

//
// Created by cat on 2018/1/2.
//#include 
#include 
#include "StringBad.h"int StringBad::nums = 0;
bool StringBad::DEBUG_LIFESTYLE = true;
bool StringBad::DEBUG_OPERATOR = true;StringBad::StringBad() {this->str = new char[1]; // 为什么要 new char[] ,为了和析构函数的 delete [] str 对应！this->str[0] = '\0';this->len = 0;if (StringBad::DEBUG_LIFESTYLE) {std::cout << StringBad::nums << "." << str << "|create..\n";}StringBad::nums++;
}StringBad::StringBad(const char *str) {size_t len = std::strlen(str);this->len = (unsigned int) len;this->str = new char[this->len + 1];std::strncpy(this->str, str, this->len + 1);if (StringBad::DEBUG_LIFESTYLE) {std::cout << StringBad::nums << "." << str << "|create##\n";}StringBad::nums++;
}StringBad::StringBad(const StringBad &obj) { // 复制构造函数 在 StringBad sb1 = sb2; 的时候调用this->len = obj.len;this->str = new char[this->len + 1];std::strncpy(this->str, obj.str, this->len + 1);if (StringBad::DEBUG_LIFESTYLE) {std::cout << StringBad::nums << "." << str << "|create^^\n";}StringBad::nums++;
}StringBad::~StringBad() {StringBad::nums--;delete[]this->str;if (StringBad::DEBUG_LIFESTYLE) {std::cout << StringBad::nums << "*" << str << "|release..\n";}
}std::ostream &operator<<(std::ostream &os, const StringBad &obj) {os << obj.str << "|toString()\n";return os;
}StringBad &StringBad::operator=(const StringBad &obj) { // 赋值运算符 在 sb1 = sb2; 的时候调用if (StringBad::DEBUG_OPERATOR) {std::cout << str << ":operator=\n";}if (this == &obj) {return *this;  // 如果是把自己赋值给自己，就直接返回自己}delete[]this->str; // 释放之前的this->len = obj.len;this->str = new char[this->len + 1]; // 申请新的std::strncpy(this->str, obj.str, this->len + 1);return *this;
}

#include 
#include "StringBad.h"using namespace std;void callStr(StringBad &sb);void callStr2(StringBad sb);int main() {const char *s1 = "比亚迪车主";const char *s2 = "东郭灰猫";const char *s3 = "南郭竽";StringBad sb(s1);   // create##StringBad sb2 = sb; // create^^StringBad sb3 = s2; // create##StringBad ss = s3; // create##cout << sb;cout << sb2;cout << sb3;callStr(sb);callStr2(sb3); // create^^ , 因为是按值传递的，所以是数据的拷贝ss = sb3; // operator=StringBad strBad; // create..std::cout << "done." << endl;return 0;
}void callStr(StringBad &sb) {cout << "callStr:" << sb;
}void callStr2(StringBad sb) {cout << "callStr2:" << sb;
}

输出效果：

0.比亚迪车主|create##
1.比亚迪车主|create^^
2.东郭灰猫|create##
3.南郭竽|create##
比亚迪车主|toString()
比亚迪车主|toString()
东郭灰猫|toString()
callStr:比亚迪车主|toString()
4.东郭灰猫|create^^
callStr2:东郭灰猫|toString()
4*东郭灰猫|release..
南郭竽:operator=
4.|create..
done.
4*|release..
3*东郭灰猫|release..
2*东郭灰猫|release..
1*比亚迪车主|release..
0*比亚迪车主|release..

Process finished with exit code 0

结合log及输出，可以看出内存管理的必要性，在自定义类中。特别是需要重写“复制构造函数”以及operator=()赋值操作符的重载。

不过，对于成员不需要内存管理的类(类成员没有需要主动使用new/malloc 进行内存申请的)，是不需要考虑内存管理的。

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