how to reverse char array using class member pointer?

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).

you have size2-1, i think it should be size2-i

yas
– yas

2014-02-04 23:25:04 +00:00
Commented Feb 4, 2014 at 23:25 — yas
– yas, Commented Feb 4, 2014 at 23:25

juanchopanza · Accepted Answer · 2014-02-04 23:26:31Z

1

You didn't mention not being able to use standard library algorithms, so

std::reverse(ptr, ptr+size);

answered Feb 4, 2014 at 23:26

juanchopanza

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Comments

Vlad from Moscow · Accepted Answer · 2014-02-04 23:54:03Z

1

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

edited Feb 4, 2014 at 23:54

answered Feb 4, 2014 at 23:34

Vlad from Moscow

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3 Comments

user3194267 Over a year ago

i tried copying the answer u placed but it still doesnt work. i even tried using reverse with the member functions that one of them i just decared now : code char* getstr () {return ptr;}; char* getstrsize() {return ptr+size;};code

Vlad from Moscow Over a year ago

I can guess that you are using a string literal as an argument of the constructor. You may not use string literals such a way. They may not be changed.

Vlad from Moscow Over a year ago

I think that your class shall dynamically allocate memory and copy argumentl in this memory. And destructor shall free this memory. Also you need to write a copy constructor and copy assignment operator.

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