在前面文章中使用过几次String类的例子，现在多重载几个运算符，更加完善一下，并且重载流类运算符。
[]运算符重载
+运算符重载
+=运算符重载
<<运算符重载
>>运算符重载
C++ Code
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#ifndef _STRING_H_
#define _STRING_H_ #include <iostream> using namespace std; class String { public: String( const char *str = ""); String( const String &other); String & operator=( const String &other); String & operator=( const char *str); bool operator!() const; char & operator[]( unsigned int index); const char & operator[]( unsigned int index) const; friend String operator+( const String &s1, const String &s2); String & operator+=( const String &other); friend ostream & operator<<(ostream &os, const String &str); friend istream & operator>>(istream &is, String &str); ~String( void); void Display() const; private: String &Assign( const char *str); char *AllocAndCpy( const char *str); char *str_; }; #endif // _STRING_H_ |
C++ Code
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#pragma warning(disable:
4996)
#include "String.h" #include <string.h> //#include <iostream> //using namespace std; String::String( const char *str) { str_ = AllocAndCpy(str); } String::String( const String &other) { str_ = AllocAndCpy(other.str_); } String &String:: operator=( const String &other) { if ( this == &other) return * this; return Assign(other.str_); } String &String:: operator=( const char *str) { return Assign(str); } String &String::Assign( const char *str) { delete[] str_; str_ = AllocAndCpy(str); return * this; } bool String:: operator!() const { return strlen(str_) != 0; } char &String:: operator[]( unsigned int index) { //return str_[index]; //non const 版本调用 const版本 return const_cast< char &>( static_cast< const String &>(* this)[index]); } const char &String:: operator[]( unsigned int index) const { return str_[index]; } String::~String() { delete[] str_; } char *String::AllocAndCpy( const char *str) { int len = strlen(str) + 1; char *newstr = new char[len]; memset(newstr, 0, len); strcpy(newstr, str); return newstr; } void String::Display() const { cout << str_ << endl; } String operator+( const String &s1, const String &s2) { //int len = strlen(s1.str_) + strlen(s2.str_) + 1; //char* newstr = new char[len]; //memset(newstr, 0, len); //strcpy(newstr, s1.str_); //strcat(newstr, s2.str_); // //String tmp(newstr); //delete newstr; //return tmp; String str = s1; str += s2; return str; } String &String:: operator+=( const String &other) { int len = strlen(str_) + strlen(other.str_) + 1; char *newstr = new char[len]; memset(newstr, 0, len); strcpy(newstr, str_); strcat(newstr, other.str_); delete[] str_; str_ = newstr; return * this; } ostream & operator<<(ostream &os, const String &str) { os << str.str_; return os; } istream & operator>>(istream &is, String &str) { char tmp[ 1024]; is >> tmp; str = tmp; return is; } |
C++ Code
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#include
"String.h"
#include <iostream> using namespace std; int main( void) { String s1( "abcdefg"); char ch = s1[ 2]; cout << ch << endl; s1[ 2] = 'A'; s1.Display(); const String s2( "xyzabc"); ch = s2[ 2]; //s2[2] = 'M'; Error s2.Display(); String s3 = "xxx"; String s4 = "yyy"; String s5 = s3 + s4; s5.Display(); String s6 = "aaa" + s3 + "sdfadfa" + "xxxx"; s6.Display(); s3 += s4; s3.Display(); cout << s3 << endl; String s7; cin >> s7; cout << s7 << endl; return 0; } |
需要注意的是，不能将String类的构造函数声明为explicit，否则 String s3 = "xxx"; 编译出错；operator[] 的non const 版本调用了const 版本的实现，其中使用了static_cast和 const_cast 两种类型转换操作符，可以参考这里；operator+ 调用了operator+= 的实现；只能将流类运算符重载为友元函数，因为第一个参数是流类引用，不是String 类。