全面的MyString

#define  _CRT_SECURE_NO_WARNINGS
#include <cstdlib>
#include <iostream>
using namespace std;
////int strlen(const char * s)
////{
//// int i = 0;
//// for (; s[i]; ++i);
//// return i;
////}
////void strcpy(char * d, const char * s)
////{
//// int i = 0;
//// for (i = 0; s[i]; ++i)
////  d[i] = s[i];
//// d[i] = 0;
////
////}
int strcmp(const char * s1, const char * s2)
{
 for (int i = 0; s1[i] && s2[i]; ++i) {
  if (s1[i] < s2[i])
   return -1;
  else if (s1[i] > s2[i])
   return 1;
 }
 return 0;
}
////void strcat(char * d, const char * s)
////{
//// int len = strlen(d);
//// strcpy(d + len, s);
////}
class MyString
{
private:
 char* ptr;
 int size;
public:
 MyString(char* s = NULL){
  if (s){
   size = strlen(s);
   ptr = new char[strlen(s) + 1];
   strcpy(ptr, s);
  }
  else{
   size = 0;
   ptr = new char[1];
   ptr[0] = 0;
  }
 }
 ~MyString(){
  delete[] ptr;
 }
 void duplicated(const MyString& s){
  if (size < s.size){
   delete[]ptr;
   ptr = new char[s.size + 1];
  }
  strcpy(ptr, s.ptr);
  size = s.size;
 }
 MyString(const MyString& s) :size(0), ptr(new char[1]){
  duplicated(s);
 }
 MyString& operator=(const char* s){
  int len = strlen(s);
  if (size < len){
   delete[] ptr;
   ptr = new char[len+ 1];
  }
  strcpy(ptr, s);
  size =len;
  return *this;
 }
 MyString& operator=(const MyString& s){
  if (ptr == s.ptr)
   return *this;
  duplicated(s);
  return *this;
 }
 char& operator[](int i){
  return ptr[i];
 }
 MyString & operator+=(const char *s){
  int len = strlen(s);
  char* tmp = new char[size+len+ 1];
  strcpy(tmp, ptr);
  strcat(tmp, s);
  delete[]ptr;
  ptr = tmp;
  size += len;
  return *this;
 }
 MyString operator()(int i, int j){
  char* tmp = new char[j + 1];
  for (int t = i; t < i + j; ++t)
   tmp[t - i] = ptr[t];
  tmp[j] = '\0';
  MyString s = tmp;
  delete[]tmp;
  return s;
 }
 friend MyString  operator+(MyString &a, MyString &b);
 friend ostream & operator<<(ostream &os, MyString & s);
 friend MyString  operator+(const char * str, MyString s);
 friend MyString operator+(MyString s, const char *str);
 friend bool operator<(MyString &s1, MyString &s2);
 friend bool operator>(MyString &s1, MyString &s2);
 friend bool operator==(MyString &s1, MyString &s2);
};
bool operator==(MyString &s1, MyString &s2){
 return strcmp(s1.ptr, s2.ptr) == 0;
}
bool operator>(MyString &s1, MyString &s2){
 return strcmp(s1.ptr, s2.ptr) > 0;
}
bool operator<(MyString &s1, MyString &s2){
 return strcmp(s1.ptr, s2.ptr) < 0;
}
MyString operator+(MyString s, const char *str){
 char* tmp = new char[strlen(s.ptr) + strlen(str) + 1];
 strcpy(tmp, s.ptr);
 strcat(tmp, str);
 MyString s1=tmp;
 delete[]tmp;
 return s1;
}
MyString  operator+(const char * str, MyString s){
 char* tmp;
 tmp = new char[strlen(str) + strlen(s.ptr) + 1];
 strcpy(tmp, str);
 strcat(tmp, s.ptr);
 MyString s1= tmp;
 delete[]tmp;
 return s1;
}
MyString  operator+(MyString &a, MyString &b){
 char* tmp = new char[strlen(a.ptr) + strlen(b.ptr)+1];
 strcpy(tmp, a.ptr);
 strcat(tmp, b.ptr);
 MyString s1 = tmp;
 delete[]tmp;
 return s1;
}
ostream & operator<<(ostream &os, MyString & s){
 os << s.ptr;
 return os;
}
int CompareString(const void * e1, const void * e2)
{
 MyString * s1 = (MyString *)e1;
 MyString * s2 = (MyString *)e2;
 if (*s1 < *s2)
  return -1;
 else if (*s1 == *s2)
  return 0;
 else if (*s1 > *s2)
  return 1;
}
int main()
{
 MyString s1("abcd-"), s2, s3("efgh-"), s4(s1);
 MyString SArray[4] = { "big", "me", "about", "take" };
 cout << "1. " << s1 << s2 << s3 << s4 << endl;
 s4 = s3;
 s3 = s1 + s3;
 cout << "2. " << s1 << endl;
 cout << "3. " << s2 << endl;
 cout << "4. " << s3 << endl;
 cout << "5. " << s4 << endl;
 cout << "6. " << s1[2] << endl;
 s2 = s1;
 s1 = "ijkl-";
 s1[2] = 'A';
 cout << "7. " << s2 << endl;
 cout << "8. " << s1 << endl;
 s1 += "mnop";
 cout << "9. " << s1 << endl;
 s4 = "qrst-" + s2;
 cout << "10. " << s4 << endl;
 s1 = s2 + s4 + " uvw " + "xyz";
 cout << "11. " << s1 << endl;
 qsort(SArray, 4, sizeof(MyString), CompareString);
 for (int i = 0; i < 4; i++)
  cout << SArray[i] << endl;
 //s1的从下标0开始长度为4的子串
 cout << s1(0, 4) << endl;
 //s1的从下标5开始长度为10的子串
 cout << s1(5, 10) << endl;
 return 0;
}