Help. Pointers problem. How to show addresses of each element of an char,string array

[mynicks]

Hello,

Problem: i think i do not grasp all the tricks of a pointer. So, i need some help please. I want to see the address of char type and string type data, please see example 2 of what i mean(it is not working,it is wrong ). How can i do it? I want to see the physical address of each element of my array and i want to use only the name: ptr (pointer) not the name of the char array(case1), string array(case2).

// example 1 - it works for int,float,double, long double data type.

#include <iostream>
#include <string>
#include <stdlib.h>

using namespace std;

int main()
{  
    int myname[3]={1,2,3};
    int *ptr;
    ptr = &myname[0]; // it is the same as: ptr= myname
         for (int i=0; i<=2; i++)
            cout << " " << ptr++ << endl;
    return 0;
}
// the above code will show me the addresses
//of each element of the int data type array: myname. 

Here come the purpose of my thread now...

//example2 - for string arrays and char arrays, how can i see
//with the cout command  the address of myname array? 
//I want to use only ptr variable to see the address 
//of each element of the array.

//case 1- char array (code problem, i need help to understand...)
    char myname[3];
    char *ptr;
    ptr = myname; //// it is the same as: ptr= &myname[0]
         for (int i=0;i<=2;i++)
            cout << " " << ptr++ << endl;

//case 2 - string array (code problem, i need help to understand...)

    string myname[]="this is a sentence .";
    string *ptr;
    ptr = &myname[0]; //// it is the same as: ptr= myname
         for (int i=0;i!='\0';i++)
            cout << " " << ptr++ << endl;

thank you for your kind help, if any :D



[]some bla bla bla below[]
I read the pointers tutorial on this forum, i submitted an example(it is example 1) to show you that i understand the basic idea of pointers. I know that the values of pointer variable = memory addresses. Then, i can have access to other variables and their values through the pointers. Also, i remember that arrays can be seen as pointers...

[keskiverto]

Operator<< is overloaded. The char* version prints a C-string.

char * ptr = ...
cout << " " << static_cast<void*>(ptr++) << endl;

However, your case 1&2 code fragments make no sense, because you don't set the ptr ...

[dhayden]

However, your case 1&2 code fragments make no sense, because you don't set the ptr ...
He sets it at lines 9 and 17.

Keskiverto is right, but there' are other problems with your second case. First of all, the condition in the for loop is wrong. it basically says i!=0 but it's using constant character 0 instead of constant integer 0. As a result the loop never executes.

And consider string myname[]="this is a sentence ."; How many elements are in that array? And what are their values? Hmm. Let's find out:

#include <iostream>
#include <string>

using namespace std;

int
main()
{
    string myname[]="this is a sentence .";
    string *ptr;
    int elements = sizeof(myname)/ sizeof(myname[0]);
    ptr = &myname[0]; //// it is the same as: ptr= myname
    for (int i=0;i<elements;i++)
        cout << myname[i] << " at " << static_cast<void*>(ptr++) << '\n';
    return 0;
}

$ ./foo
this is a sentence . at 0x22ac1c
this is a sentence . at 0x22ac20
this is a sentence . at 0x22ac24
this is a sentence . at 0x22ac28
this is a sentence . at 0x22ac2c
this is a sentence . at 0x22ac30
this is a sentence . at 0x22ac34
this is a sentence . at 0x22ac38
this is a sentence . at 0x22ac3c
this is a sentence . at 0x22ac40
this is a sentence . at 0x22ac44
this is a sentence . at 0x22ac48
this is a sentence . at 0x22ac4c
this is a sentence . at 0x22ac50
this is a sentence . at 0x22ac54
this is a sentence . at 0x22ac58
this is a sentence . at 0x22ac5c
this is a sentence . at 0x22ac60
this is a sentence . at 0x22ac64
this is a sentence . at 0x22ac68
this is a sentence . at 0x22ac6c

What the heck?!? It's possible that I've stumbled on a bug in MinGW. Let's look at that declaration again:
string myname[]="this is a sentence .";
"this is a sentence ." is an array of const chars that is 21 elements long. That explains why myname has 21 elements. But I don't know why they all have the same value. It seems like a bug to me. Maybe someone else can comment.

[keskiverto]

The whole concept of using plain array of strings is very strange.

That array declaration seems to create an array with 21 std::string objects and initialize each of them with C-string "this is a sentence ."

If you would use
string myname[] = { "this is a sentence ." };
The array would have only one element, one string, which stores the "this is a sentence ."

C++ has many rules about initialization.


PS. one does not need to cast a pointer to string into void pointer, because that conversion is implicit and thus the address of the string object will print. Only the char pointer is special.