简单String类功能实现
一般是要求实现构造函数、拷贝构造函数、赋值函数、析构函数这几个非常重要的部分。因为String里涉及动态内存的管理，默认的拷贝构造函数在运行时只会进行浅复制，即只复制内存区域的指针，会造成两个对象指向同一块内存区域的现象。如果一个对象销毁或改变了该内存区域，会造成另一个对象运行或者逻辑上出错。这时就要求程序员自己实现这些函数进行深复制，即不止复制指针，需要连同内存的内容一起复制。
具体代码如下：
/****************** Author : 杨永利 data : 2020-06-28 *******************/ #include <string.h> #include <assert.h> #include <iostream> using namespace std; class String { public: String(const char *str = NULL); //通用构造函数 String(const String &str); //拷贝构造函数(深赋值) ~String(); //析构函数 String operator+(const String &str) const; //重载+ String& operator=(const String &str); //重载= String& operator+=(const String &str); //重载+= bool operator==(const String &str) const; //重载== char& operator[](int n) const{assert(n <= length - 1); return data[n]; } //重载[](内联函数) size_t size() const{ return length; } //长度接口(内联函数) const char* c_str() const{ return data; } //数据接口(内联函数) friend istream& operator>>(istream &is, String &str);//输入 friend ostream& operator<<(ostream &os, String &str);//输出 private: char *data; //字符串 size_t length; //长度 }; String::String(const char *str) { if(str == NULL) { length = 0; data = new char[1]; *data = '\0'; }else{ length = strlen(str); data = new char[length + 1]; strcpy(data, str); } } String::String(const String &str) { length = str.size(); data = new char[length + 1]; strcpy(data, str.c_str()); } String::~String() { delete []data; length = 0; } String String::operator+(const String &str) const { String newString; newString.length = length + str.size(); newString.data = new char[newString.length + 1]; strcpy(newString.data, data); strcat(newString.data, str.data); return newString; } String& String::operator=(const String &str) { if(this == &str) { return *this; } delete []data; length = str.size(); data = new char[length + 1]; strcpy(data, str.c_str()); return *this; } String& String::operator+=(const String &str) { if(str.size() == 0) { return *this; } length += str.size(); char *t_data = new char[length + 2]; strcpy(t_data, data); strcat(t_data, str.c_str()); delete []data; data = t_data; return *this; } bool String::operator==(const String &str) const { if(length == str.size() && !strcmp(data, str.c_str())) { return true; } return false; } istream& operator >>(istream &is, String &str) { char temp[1024]; is >> temp; str.length = strlen(temp); str.data = new char[str.length + 1]; strcpy(str.data, temp); return is; } ostream& operator<<(ostream &os, String &str) { os << str.data; return os; } int main() { String s; cin >> s; cout << s << ": " << s.size() << endl; char a[] = "Hello", b[] = "World!"; String s1(a), s2(b); cout << s1 << " + " << s2 << " = " << s1 + s2 << endl; String s3 = s1 + s2; if (s1 == s3) cout << "First: s1 == s3" << endl; s1 += s2; if (true == (s1 == s3)) cout << "Second: s1 == s3" << endl; cout<<s1[3]<<endl; return 0; }
运行结果如下：
