C++自定义String字符串类
实现了各种基本操作，包括重载+号实现String的拼接
findSubStr函数，也就是寻找目标串在String中的位置，用到了KMP字符串搜索算法。
#include <iostream>
#include <cstring>
using namespace std;
class String;
class Data{ // 抽象基类Data
public:
virtual const int compareTo(const String& target) const = 0; // virtual比较函数
};
class String: public Data{ // String类。继承自Data
public:
static int num_strings; // 程序周期内创建的String对象个数
static const int CINLIM = 80; // 限制字符长度
String(); // 默认构造函数
String(unsigned int capacity); // 以大小为capacity来初始化
String(unsigned int capacity, char ch); // 填充字符为ch，大小为capacity
String(const char* target); // 以一个c风格字符串初始化
String(const String& st); // 拷贝构造函数
~String(){ delete ptr; } // 析构函数
const int findSubStr(const char* substr) const; // 找出子串位置
const int findChar(char target) const; // 找出字符第一次出现位置
const int length() const; // 返回字符串大小
static int howManyExit(); // 返回程序周期内创建的String对象个数
const int compareTo(const String& target) const override; // 与其它String对象比较大小
String& operator=(const String&); // 重载赋值操作符
String& operator=(const char*); // 重载赋值操作符
friend String operator+(const String&,const String&) ; // 重载加号
char& operator[](int i); // 重载[]
const char& operator[](int i) const; // 重载[]
friend bool operator>(const String& st1,const String& st2); // 重载>
friend bool operator<(const String& st1,const String& st2); // 重载<
friend bool operator==(const String& st1,const String& st2); // 重载==
friend ostream& operator<<(ostream& os,const String& st); // 重载<<
friend istream& operator>>(istream& is,String& st); // 重载>>
private:
char* ptr; // 内置char数组指针
unsigned int len; // 当前String长度
};
int String::num_strings = 0; // 静态变量初始化
String::String() { ptr = new char[10]; len = 10; }
String::String(unsigned int capacity){
ptr = new char[capacity]; len = capacity;
++ num_strings;
}
String::String(unsigned int capacity, char ch){
ptr = new char[capacity]; len = capacity;
for(int i=0;i<len;i++)
ptr[i] = ch;
++ num_strings;
}
String::String(const char* target){
int tmp = (int)strlen(target);
len = (unsigned)tmp;
ptr = new char[len];
strcpy(ptr,target);
++ num_strings;
}
String::String(const String& st){
int tmp = (int)strlen(st.ptr);
len = (unsigned)tmp;
ptr = new char[len];
strcpy(ptr,st.ptr);
++ num_strings;
}
const int String::findSubStr(const char* substr) const{
int next[100];
next[0] = -1;
int i=0,j=-1;
int lenP = (int)strlen(substr);
while(i<lenP){
if(j==-1||substr[i]==substr[j]){
++i; ++j;
next[i] = j;
}else
j = next[j];
}
i = 0,j = 0;
while(i<len&&j<lenP){
if(j==-1|ptr[i]==substr[j]){
++i; ++j;
}else
j = next[j];
}
if(j==lenP) return len - j;
return -1;
}
const int String::findChar(char target) const{
for(int i=0;i<len;i++)
if(ptr[i] == target) return i;
return -1;
}
const int String::length() const{
return this->len;
}
int String::howManyExit(){
return num_strings;
}
const int String::compareTo(const String& target) const{
if(target.ptr == nullptr || strcmp(ptr,target.ptr)>0)
return 1;
else if(strcmp(ptr,target.ptr)==0)
return 0;
else
return -1;
}
String& String::operator=(const String& str){
if(this == &str)
return *this;
delete ptr;
len = (int)strlen(str.ptr);
ptr = new char[len];
strcpy(ptr,str.ptr);
return *this;
}
String& String::operator=(const char* str){
delete[] ptr;
len = (int)strlen(str);
ptr = new char[len+1];
strcpy(ptr,str);
return *this;
}
String operator+(const String& st1,const String& st2){
int lenSt2 = (int)strlen(st2.ptr);
int lenSt1 = (int)strlen(st1.ptr);
char* temp = new char[lenSt1+lenSt2+1];
strcpy(temp,st1.ptr);
for(int i=lenSt1;i<lenSt1+lenSt2;i++)
temp[i] = st2.ptr[i-lenSt1];
return String(temp);
}
char& String::operator[](int i){
return ptr[i];
}
const char& String::operator[](int i) const{
return ptr[i];
}
bool operator<(const String& st1,const String& st2){
return (std::strcmp(st1.ptr,st2.ptr)<0);
}
bool operator>(const String& st1,const String& st2){
return (std::strcmp(st1.ptr,st2.ptr)>0);
}
bool operator==(const String& st1,const String& st2){
return (std::strcmp(st1.ptr,st2.ptr)==0);
}
ostream& operator<<(ostream& os,const String& st){
os<<st.ptr;
return os;
}
istream& operator>>(istream& is,String& st){
char temp[String::CINLIM];
is.get(temp,String::CINLIM);
if(is)
st = temp; //在此处" = "已被重载过了
while(is && is.get()!='\n')
continue;
return is;
}
int main()
{
String A = "abcd";
String B = "efgh";
String C = A + B;
cout << C << endl;
}