C++面试常见问题：手写String类

#include 
#include 
using namespace std;
class String
{
public:
    String(const char *str);       //构造函数
    String(const String &other);          //拷贝构造函数
    String(String &&other);               //移动构造函数
    ~String();                            //析构函数
    String &operator=(const String &str); //重载赋值运算符
    String &operator=(String &&str);      //重载移动赋值运算符
private:
    char *data;
};

String::String(const char *str = "\0")
{
    if (str == NULL) //如果实参为空
    {
        data = (char *)malloc(sizeof(char) * 1);
        data[0] = '\0';
    }
    else
    {
        int len = strlen(str);
        data = (char *)malloc(sizeof(char) * (len + 1)); //多开一个，存 '\0'
        strcpy(data, str);
    }
}
String::String(const String &other)
{
    int len = strlen(other.data);
    data = (char *)malloc(sizeof(c
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