C++实现简易版字符串类

  1 #include<bits/stdc++.h>
  2 using namespace std;
  3 
  4 class String {
  5 private:
  6     char *ptr;    //字符串首指针 
  7     size_t len;    //字符串长度 
  8     
  9 public:
 10     String(const char *str=NULL);    //构造函数 
 11     String(const String &str);    //复制构造函数 
 12     ~String();    //析构函数 
 13     
 14     friend String operator + (const String& str1,const String& str2);    //重载加号 
 15     
 16     String& operator = (const String& str);    //重载赋值运算符 
 17     String& operator += (const String& str);    //重载+= 
 18     bool operator == (const String &str);    //重载相等判断符 
 19     char& operator [] (int n);    //重载下标取值 
 20     
 21     bool operator != (const String& str) const;
 22     bool operator < (const String& str) const;
 23     bool operator <= (const String& str) const;
 24     bool operator > (const String& str) const;
 25     bool operator >= (const String& str) const;
 26     
 27     size_t size() const;    //返回长度 
 28     const char* c_str() const;    //获得String的C风格字符串 
 29     
 30     //输入输出运算 
 31     friend istream& operator >> (istream &is,String &str);
 32     friend ostream& operator << (ostream &os,String &str);    
 33 };
 34 
 35 //字符串拷贝函数：把strSrc串拷贝到strDest串 
 36 char* strcpy(char *strDest,const char *strSrc) {
 37     if (strDest==NULL || strSrc==NULL) return NULL;
 38     if (strDest==strSrc) return strDest;
 39     char *head=strDest;    //先把首指针保存一份用来输出 
 40     while ((*strDest++ = *strSrc++) != ‘\0‘);
 41     return head; 
 42 }
 43 
 44 String::String(const char *str) {
 45     if (str==NULL) {    //构造为空串 
 46         this->len=0;
 47         this->ptr=new char[1];
 48         *ptr=‘\0‘;
 49     } else {
 50         this->len=strlen(str);
 51         this->ptr=new char[this->len+1];    //为什么+1，考虑‘\0‘ 
 52         strcpy(this->ptr,str);
 53     }
 54 }
 55 String::String(const String &str) {
 56     this->len=str.len;
 57     this->ptr=new char[this->len+1];
 58     strcpy(this->ptr,str.ptr);
 59 }
 60 String::~String() {
 61     delete []this->ptr;
 62     this->len=0;
 63 }
 64 
 65 size_t String::size() const {
 66     return this->len;
 67 }
 68 const char* String::c_str() const {
 69     return this->ptr;
 70 }
 71 
 72 String operator + (const String& str1,const String& str2) {
 73     String newString;
 74     newString.len=str1.len+str2.len;
 75     newString.ptr=new char[newString.len+1];
 76     strcpy(newString.ptr,str1.ptr);
 77     strcat(newString.ptr,str2.ptr);
 78     return newString;
 79 }
 80 String& String::operator = (const String& str) {
 81     if (this==(&str)) return *this;
 82     //这一步很关键，先把以前的空间删掉再赋值，否则空间泄露 
 83     delete []this->ptr;
 84     
 85     this->len=str.len;
 86     this->ptr=new char[this->len+1];
 87     strcpy(this->ptr,str.ptr);
 88     return *this;
 89 } 
 90 String& String::operator += (const String& str) {
 91     //+=和上面的=同理，注意把以前的空间先释放
 92     char *tmp=this->ptr;
 93     *this=*this+str;
 94     delete []tmp;
 95     return *this;
 96 }
 97 //内联函数加快运行速度
 98 inline bool String::operator == (const String& str) {
 99     if (this->len!=str.len) return 0;
100     for (int i=0;i<this->len;i++)
101         if (*(this->ptr+i) != *(str.ptr+i)) return 0;
102     return 1;     
103 }
104 char& String::operator [] (int n) {
105     //if (n>this->len-1) throw;  //越界异常
106     return *(this->ptr+n); 
107 }
108 
109 bool String::operator != (const String& str) const {
110     if (this->len!=str.len) return 1;
111     for (int i=0;i<this->len;i++)
112         if (*(this->ptr+i) != *(str.ptr+i)) return 1;
113     return 0;
114 }
115 bool String::operator < (const String& str) const {
116     int minlen=min(this->len,str.len);
117     bool ret=0; int equal_point=-1;
118     for (int i=0;i<minlen;i++)
119         if (*(this->ptr+i) != *(str.ptr+i)) {
120             if (*(this->ptr+i) < *(str.ptr+i)) ret=1;
121             break;
122         } else equal_point=i;
123     if (equal_point==minlen-1 && this->len-1==equal_point && str.len-1>equal_point) ret=1;    
124     return ret;    
125 }
126 bool String::operator > (const String& str) const {
127     int minlen=min(this->len,str.len);
128     bool ret=0; int equal_point=-1;
129     for (int i=0;i<minlen;i++)
130         if (*(this->ptr+i) != *(str.ptr+i)) {
131             if (*(this->ptr+i) > *(str.ptr+i)) ret=1;
132             break;
133         } else equal_point=i;
134     if (equal_point==minlen-1 && this->len-1>equal_point && str.len-1==equal_point) ret=1;
135     return ret;    
136 }
137 
138 istream& operator >> (istream &is,String &str) {
139     char s[100]; scanf("%s",s);
140     str.len=strlen(s);
141     strcpy(str.ptr,s);
142 }
143 ostream& operator << (ostream &os,String &str) {
144     for (int i=0;i<str.len;i++)
145         os<<*(str.ptr+i);
146     return os;
147 }
148 
149 int main()
150 {
151     String s1; cin>>s1; cout<<s1<<endl;
152     //这里的串会当成C语言字符串，调用构造函数 
153     String s2("AqA"); cout<<s2<<endl;    
154     //这里的s2就是String类了，调用复制构造函数 
155     String s3(s2); cout<<s3<<endl;
156     
157     String s4(s2+s1+s3); cout<<s4<<endl;
158     //这里的"11"会自动转成String ？ 
159     String s5=s4+"11"; cout<<s5<<endl;
160     
161     cout<<s5[3]<<endl;
162     cout<<"s2==s3 ? "<<(s2==s3)<<endl;
163     cout<<"s1==s3 ? "<<(s1==s3)<<endl;
164     
165     //这里测试各种比较符号
166     String s6("AAbb");
167     String s7("AAbb");
168     String s8("AAbba");
169     String s9("AAbab");
170     cout<<"s6==s7 ? "<<(s6==s7)<<endl;
171     cout<<"s6>s7 ? "<<(s6>s7)<<endl;
172     cout<<"s6<s7 ? "<<(s6<s7)<<endl;
173     cout<<"s6>s8 ? "<<(s6>s8)<<endl;
174     cout<<"s6<s8 ? "<<(s6<s8)<<endl;
175     cout<<"s8>s9 ? "<<(s8>s9)<<endl;
176     cout<<"s7>s9 ? "<<(s7>s9)<<endl; 
177     return 0;
178 }