problem with Pointers and array

This is a discussion on problem with Pointers and array within the C++ Programming forums, part of the General Programming Boards category; Hi, I'm trying to write a simple program to learn and use array and pointer. It copies values from a ...

  1. #1
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    Jan 2011
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    problem with Pointers and array (SOLVED)

    Hi,
    I'm trying to write a simple program to learn and use array and pointer. It copies values from a vector to an array and prints the value of the array. Here is the portion of the code that causes problem:

    Code:
        int *pArr = new int[vect.size()] ;
        int *pArrBegin = pArr ;
        for ( vector<int>::iterator itr = vect.begin() ; itr != vect.end() ; itr++ ) {
            int *pItr = pArr;
            *pItr =  * itr ;
            pItr++ ;
        }
    
        cout << "Print Array: " << endl ;
        for ( int *pArrItr = pArrBegin  , *pArrEnd = pArr + vect.size(); pArrItr != pArrEnd; pArrItr++ ){
            cout << * pArrItr << " " ;
        }
    Here is the output:
    Code:
     
     ./copyVectorToArray 
    1 2 3 4 
    Print vec: 
    1 2 3 4 
    Print Array: 
    4 0 0 0
    I just don't understand why when I increment pltr, pArr and pArrBegin is also incremented.
    Last edited by platoali; 01-07-2011 at 01:13 PM.

  2. #2
    Registered User hk_mp5kpdw's Avatar
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    Code:
    for ( vector<int>::iterator itr = vect.begin() ; itr != vect.end() ; itr++ ) {
        int *pItr = pArr;
        *pItr =  * itr ;
        pItr++ ;
    }
    Being local to the loop, it gets recreated each iteration of the loop and is always pointing to first slot in the allocated memory at the point of the assignment below what I've marked. Thus, the remaining slots never get filled with data.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  3. #3
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    problem with Pointers and array (SOLVED)

    Thank you very much. It works now.

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