构造函数

代码语言：javascript

AI代码解释

//无参的默认构造 string::string() :_str(new char[1]{'\0'}) ,_size(0) ,_capacity(0) {} //带参的构造 string::string(const char* str) :_size(strlen(str)) //,_size(strlen(str)) //,_capacity(strlen(str)) { cout << "构造" << endl; _capacity = _size; _str = new char[_size+1];//开跟str一样大的空间 还要加1 给\0预留空间 memcpy(_str, str, _size+1); }

带参的构造中有一个细节：不要使用三个strlen 因为strlen效率不高。因为初始化列表有一个按照声明顺序初始化的逻辑,所以初始化列表与声明顺序是有关联关系的，如果实在不好在初始化列表初始化那就在函数体内部初始化。

1.2析构函数

代码语言：javascript

AI代码解释

//析构函数 string::~string() { delete[] _str; _str = nullptr; _size = 0; _capacity = 0; }

1.3拷贝构造

代码语言：javascript

AI代码解释

//拷贝构造 string::string(const string& s) { //开辟新空间 _str = new char[s._capacity+1]; //拷贝旧数据 memcpy(_str, s._str, s._size+1); _size = s._size; _capacity = s._capacity; }

拷贝构造要注意开辟空间和拷贝数据的时候一定不要忘记给\0预留一个空间，因为**string**内部的**_size(有效数据个数)**它指向的是最后一个数据的下一个位置的数据也就是**\0**，而且字符串一般以**\0**作为结束的标识符。

1.4赋值重载

代码语言：javascript

AI代码解释

string& string::operator=(string& s) { //防止给自己赋值 if (this != &s) { //开新空间拷贝旧数据 char* tmp = new char[s._size + 1]; memcpy(tmp, s._str, s._size + 1); delete[] _str; _str = tmp; _size = s._size; _capacity = s._capacity; } return *this; }

对于拷贝构造和赋值重载还有一些现代写法，现代写法相比于传统的写法更加简洁。内部的逻辑其实就是调用std里面的swap交换底层的成员变量来实现的，如果想了解请点击：

1.5再探深浅拷贝问题

之前在类和对象时我们说过如果一个有资源的类我们在没有显示写拷贝构造和赋值重载的时候，使用编译器默认生成的拷贝构造那么完成的就是浅拷贝：

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