processing dynamic arrays

Hello all,

While learning about dynamic arrays, I'm asked by C++ primer to do the following exercise:

Quote:

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Write a program to read the standard input and build a vector of ints from values that are read. Allocate an array of the same size as the vector and copy the elements from the vector into the array.

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I came up with what you can see below. I would like to know, is it possible to simplify the for loop where I assign to the dynamic array? Specifically, can I do this without creating a pointer to the dynamic array while making sure I do not overflow?

Code:

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#include <cstdlib>
#include <iostream>
#include <vector>
#include <iterator>

int main()
{
    using namespace std;
   
    int input;
    vector<int> iv;

    while (cin >> input) {
        iv.push_back(input);
    }
    cout << endl;

    for (vector<int>::const_iterator i = iv.begin(); i != iv.end(); ++i) {
        cout << *i << "\t";
    }
    cout << endl;

    int *p = new int[iv.size()];
    vector<int>::size_type i = 0;
    for (int *pp = p; pp != p + iv.size(); ++pp, ++i) {
        *pp = iv[i];
        cout << *(p + i) << "\t";
    }
    cout << endl;

    delete[] p;


    system("PAUSE");
        return 0;
}

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If you don't know the size of the array at compile time you will have to dynamically allocate it.
But you could use copy from <algorithm> to fill the array

Code:

---

#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>

int main()
{
    using namespace std;
   
    int input;
    vector<int> iv;

    while (cin >> input) {
        iv.push_back(input);
    }
    cout << endl;

    for (vector<int>::const_iterator i = iv.begin(); i != iv.end(); ++i)
        cout << *i << "\t" ;
   
    cout << endl;

    int *p = new int[iv.size()];
   
    copy(iv.begin(), iv.end(), p );
   
    for ( int i = 0; i < iv.size(); ++i )
        cout << p[i] << "\t" ;
    cout << endl;

    delete[] p;

    return 0;
}

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Kurt

Um, you could use array indices instead of the pointer. You could assign things to the array when you are printing out the vector. I don't know. This is kind of frivolous.

Not sure if you are asking if you can do it without creating a "dynamic" array or not, but in case you are asking if you can do it via a static array you can simply just do:

Code:

---

#include <vector>
#include <algorithm>
#include <iostream>

using namespace std;

int main(void)
{
        vector<int> ivec;
        int input;

        while (cin >> input) {
                        ivec.push_back(input);
        }

        int iarray[ivec.size()];
        copy(ivec.begin(), ivec.end(), iarray);

        // test: print
        for (int i = 0; i < ivec.size(); i++) {
                        cout << iarray[i] << endl;
        }

        return 0;
}

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Not sure what your asking though :)

Quote:

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Originally Posted by 0rion

Not sure if you are asking if you can do it without creating a "dynamic" array or not, but in case you are asking if you can do it via a static array you can simply just do:)

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That works with gnu compiler only. std C++ doesn't allow that.
compile with

Code:

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g++ ex.cc --pedantic

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Kurt

I reread my question after the frivolous adjective has been given to it.

You are right, as was Tonto. It's a confusing question. And more so because I didn't even remember that *(p + i) yields an lvalue. As such, the final loop could have been replaced with...

Code:

---

    for (vector<int>::size_type i = 0; i != iv.size(); ++i) {
        *(p + i) = iv[i];
        cout << *(p + i) << "\t";
    }

---

Much simpler...
Dunno, I drew a blank or something. Couldn't see that when I was answering the exercise.

> *(p + i) = iv[i];
Why not

Code:

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p[i] = iv[i];

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hmm... because i'm a newb, that's why :)

You are right. Since I allocated it, I didn't remember that I couldn't simply access it by name without dereferencing it.

Ugh... arrays and pointers are killing me!

Indeed.

http://c-faq.com/ptrs/index.html
http://c-faq.com/aryptr/index.html
http://c-faq.com/malloc/index.html

Some relevant info.

Also, for now
http://home.netcom.com/~tjensen/ptr/cpoint.htm

And for later
http://www.newty.de/fpt/index.html