why cant i reverse char array using pointer??

[alsade]

can someone please tell me whats wron with my code?

#include <iostream>
#include <cstring>
#include <string>

using namespace std;

class my_string
{
    char* ptr;
    int size;
public:
    my_string(){};
    my_string(char *str=""){size = strlen(str);ptr  =str;}
	my_string(const my_string &obj);
	my_string& operator= (const my_string& obj);
    char* getstr () {return ptr;};
    void reverse();
    int find (char);
    void print();
	~my_string(){delete [] ptr;};
};

my_string::my_string(const my_string &obj)
{
	ptr=new char;
	strcpy_s(ptr,50,obj.ptr);
	size=obj.size;
}

my_string& my_string:: operator= (const my_string& obj)
{
    strcpy_s(ptr,50,obj.ptr);
	size=obj.size;
	return *this;
}



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;
     }
     ptr[size] = '\0';
}

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");
	my_string s2=s1;
        s1.print(); 
	s1.reverse();
	s1.print();
}

[TwilightSpectre]

What errors are you getting, and if you aren't getting errors, what is wrong exactly? Please specify, and gives us as much information as you can.

[coder777]

line 25: Change

ptr=new char;

To

ptr=new char[obj.size]; // assuming that obj.size includes the terminating 0 (otherwise + 1)

line 26: Why 50? Use size instead

line 13: This will very likely lead to a crash on line 20

[alsade]

@NT3
im not gettin any errors but the output im gettin is :

abcde
abcde

and then the program crashes...

@coder777

i changed line 25.
line 26 when i tried changing it to size/+1 the program crashed before i got any output.

and can u plz explain why line 13 will lead to a crash in line 20?

[cire]

and can u plz explain why line 13 will lead to a crash in line 20?

The only case where you should use delete[] is on memory that has been allocated with new[].

[JLBorges]

#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>

using namespace std;

class my_string
{
    char* ptr;
    int size;
public:
    // my_string(){};
    // my_string(char *str="") // {size = strlen(str);ptr  =str;}

    my_string( const char* cstr = "" ) // also the default constructor
    {
        size = strlen(cstr) ;
        ptr = new char[ size + 1 ] ; // allocate memory for size+1 chars;
                                      // +1 for the null char
	strcpy( ptr, cstr ) ;
    }

    my_string(const my_string &obj);
    my_string& operator= (const my_string& obj);
    char* getstr () {return ptr;};
    void reverse();
    int find (char);
    void print();
	~my_string(){delete [] ptr;};
};

my_string::my_string(const my_string &obj)
{
	// ptr=new char;
	ptr = new char[ obj.size + 1 ] ; // allocate sufficient memory

	// strcpy_s(ptr,50,obj.ptr); // *** avoid; non-standard
	strcpy( ptr, obj.ptr ) ;

	size=obj.size;
}

my_string& my_string:: operator= (const my_string& obj)
{
    if( this != &obj ) // check for self-assignment
    {
        delete[] ptr ; // do what the desructor does

        // then do what the copy constructor does
        ptr = new char[ obj.size + 1 ] ; // +1 for the null char
        strcpy( ptr, obj.ptr ) ;
        size=obj.size;
    }
    return *this ;
}

void my_string::reverse()
{
    int left = 0 ; // position of first char
    int right = size - 1 ; // position of  char just before the null char
                            // (leave the null character where it is )
    while( left < right )
    {
        std::swap( ptr[left], ptr[right] ) ;
        ++left ;
        --right ;
    }
}

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");
	my_string s2=s1;
        s1.print();
	s1.reverse();
	s1.print();
}

[alsade]

working! great thank you very much!