这道题是运算符重载、动态内存分配的很好的例题
#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
{
// 在此处补充你的代码
};
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;
}
样例输入
无
样例输出
- abcd-efgh-abcd-
- abcd-
- abcd-efgh-
- efgh-
- c
- abcd-
- ijAl-
- ijAl-mnop
- qrst-abcd-
- abcd-qrst-abcd- uvw xyz
about
big
me
take
abcd
qrst-abcd-
分析
- 需要在private声明
char* ptr- 构造函数：
MyString(const char* s)、MyString()以及MyString(const MyString& s)，其中，默认构造函数不是空字符nullptr，而是有一个""的字符…，然后要有析构函数- 需要用到的运算符：
[ ]、类.operator+(类）、
= (类或字符串指针）、<<、+=、( )- 需要注意是返回引用还是返回值，这个特别要注意。如果返回引用则会修改*this的值，如果返回值则只是暂时的副本。
- 返回bool的
== > <运算符。- 最好要讨论是否为空指针的情况，然后再决定是否分配内存。
if(p) { ptr = new char[strlen(p)]; strcpy(ptr,p);} else { ptr = new char[1]; ptr[0]='\0';}
private:
char *p;
public:
MyString(const char * s = NULL)
{
if (s)
{
p = new char[strlen(s) + 1];
strcpy(p, s);
}
else
{
p = new char[1];
p[0] = '\0';
}
}
~MyString()
{
if (p) delete[] p;
}
MyString(const MyString &s)
{
if (s.p)
{
p = new char[strlen(s.p) + 1];
strcpy(p, s.p);
}
else
{
p = new char[1];
p[0] = '\0';
}
}
MyString & operator=(const char * s)
{
if (p == s)
return *this;
delete[] p;
if (s)
{
p = new char[strlen(s) + 1];
strcpy(p, s);
}
else
{
p = new char[1];
p[0] = '\0';
}
return *this;
}
MyString & operator=(const MyString & s)
{
if (p == s.p)
return *this;
delete[] p;
if (s.p)
{
p = new char[strlen(s.p) + 1];
strcpy(p, s.p);
}
else
{
p = new char[1];
p[0] = '\0';
}
return *this;
}
friend MyString operator+(MyString &a, MyString &b)
{
char *temp = new char[strlen(a.p) + strlen(b.p)];
strcpy(temp, a.p);
strcat(temp, b.p);
return MyString(temp);
}
friend ostream & operator<<(ostream &os, MyString & s)
{
os << s.p;
return os;
}
char & operator[](int i)
{
return p[i];
}
MyString & operator+=(const char *s)
{
char* temp = new char[strlen(p)+1];
strcpy(temp, p);
delete[] p;
p = new char[strlen(temp) + strlen(s)+1];
strcpy(p, temp);
strcat(p, s);
return *this;
}
friend MyString operator+(const char * str, MyString s )
{
char *temp = new char[strlen(str) + strlen(s.p)+1];
strcpy(temp,str);
strcat(temp, s.p);
return MyString(temp);
}
friend MyString operator+(MyString s, const char *str)
{
char *temp = new char[strlen(s.p) + strlen(str) + 1];
strcpy(temp, s.p);
strcat(temp, str);
return MyString(temp);
}
friend bool operator<(MyString &s1, MyString &s2)
{
if (strcmp(s1.p, s2.p) < 0)
return true;
else
return false;
}
friend bool operator>(MyString &s1, MyString &s2)
{
if (strcmp(s1.p, s2.p) > 0)
return true;
else
return false;
}
friend bool operator==(MyString &s1, MyString &s2)
{
if (strcmp(s1.p, s2.p) == 0)
return true;
else
return false;
}
char * operator () (int start, int length)
{
char * temp = new char[length+1];
for (int i = start; i < start+length; i++)
{
temp[i - start] = p[i];
}
temp[length] = '\0';
return temp;}
最后一个()运算符重载值得学习.