how to reverse char array using class member pointer? - c++

Question

im tryin to reverse an array using pointer which is a class member:
#include <iostream>
#include <cstring>
#include <string>
using namespace std;
class my_string
{
char* ptr;
int size;
public:
my_string(){};
my_string(char* str) : ptr(str),size(strlen(ptr)){};
char* getstr () {return ptr;};
void reverse();
int find (char);
void print();
};
void my_string::reverse()
{
int size2=size;
for (int i=0;i<(size/2);i++)
{
char tmp=ptr[i];
ptr[i]=ptr[size2-1];
ptr[size2-1]=ptr[i];
size2--;
}
}
int my_string::find(char c)
{
for (int i=0;i<size;i++)
{
if (ptr[i]==c)
return i;
}
return -1;
}
void my_string::print()
{
for (int i=0;i<size;i++)
cout<<ptr[i];
cout<<endl;
}
int main()
{
my_string s1("abcde");
s1.print();
s1.reverse();
s1.print();
}
im not gettin any errors but the reverse function is surely not working.
can someone please explain to me why?
*this is an homework assignment asking me not to use dynamic allocation or strings (for now).

Answer 1

You didn't mention not being able to use standard library algorithms, so
std::reverse(ptr, ptr+size);

Answer 2

You can use standard algorithm std::reverse declared in header <algorithm>.
For example
std::reverse( ptr, ptr + size );
But if you want to do it yourself then the function could look the following way
void my_string::reverse()
{
for ( int i = 0; i < size/2; i++ )
{
char tmp = ptr[i];
ptr[i] = ptr[size-1-i];
ptr[size-1-i] = tmp;
}
}
A test program
#include <iostream>
#include <cstring>
int main()
{
char s[] = "123456789";
char *ptr = s;
int size = std::strlen( ptr );
std::cout << s << std::endl;
for ( int i = 0; i < size/2; i++ )
{
char tmp = ptr[i];
ptr[i] = ptr[size-1-i];
ptr[size-1-i] = tmp;
}
std::cout << s << std::endl;
}
Output is
123456789
987654321