class中缺省的4个函数的实现

#include <iostream>
using namespace std;
class myString
{
public:
myString(const char *str=NULL);
myString(const myString &other);
~myString();
myString & operator=(const myString &other);
showString();
private:
char *m_data;

};

myString::~myString()
{
delete [] m_data;
}
myString::myString(const char *str)
{
if (str == NULL)
{
m_data = new char[1];
*m_data = '\0';
}
else
{
int length = strlen(str)+1;
m_data = new char[length];
while(*str != '\0')
*m_data++ = *str++;
*m_data = '\0';
}
}
myString::myString(const myString &other)
{
int length = strlen(other.m_data)+1;
m_data = new char(length);
strcpy(m_data,other.m_data);
*m_data = '\0';
}
myString & myString::operator=(const myString &other)
{
if (this == &other)
{
return *this;
}
delete []m_data;
int length = strlen(other.m_data)+1;
m_data = new char[length];
strcpy(m_data,other.m_data);
return *this;
}
myString::showString()
{
cout<<this->m_data<<endl;
}
int main(int argc,char **argv)
{
myString str;
char *p = "hello peter";
myString dest(p);
dest.showString();
str = dest;
str.showString();
return 0;
}