dynamically allocating array

[metulburr]

I still dont understand pointers and references really. I found this segment of code somewhere on the forums. I was trying to convert it to a function to help learn how to dynamically allocate an array.

#include <iostream>
using namespace std;





int main(){
    int *exampleArray;

    cout << "Array output inside creation loop..." << endl;
    exampleArray = new int[10]; //allocate enough memory for 10 int's
    for(int i = 0; i < 10; i++)
    {
        // exampleArray = new int;
        exampleArray[i] = i;
        cout << exampleArray[i] << endl;
    }

    cout << endl << "Array output outside creation loop..." << endl;
    for(int i = 0; i < 10; i++)
        cout << exampleArray[i] + 1<< endl;




    delete exampleArray;
}

I think i understand somewhat whats going on, but what confuses me is its all in main, so the size of the array is known, and automatically makes me think of just making int var[10]; instead. so i figured if i just make it to a function i could see the value in it.

I was trying to make it something like this:

int * array;
array = make_array_size_of(10);
cout << "last index is" << array[9];

I know something like vector can make an unknown array size, but i havent learned it yet. So is the way possible or must i learn vectors to accomplish this?

[Athar]

Arrays allocated using new[] must be deleted using delete[], not delete.

I know something like vector can make an unknown array size, but i havent learned it yet. So is the way possible or must i learn vectors to accomplish this?

Yes, you can do it using dynamic allocation. vectors do something similar internally.

[metulburr]

so in the example code

this:
delete[] exampleArray;

instead of:
delete exampleArray;
?

[Athar]

That's right.

[metulburr]

so this is what i came up with

#include <iostream>
using namespace std;

int make_array_size(int size){
    int *array;
    array = new int[size];

    for (int i=0; i < size; i++){
        cout << "created array[" << i << "]" << endl;
    }
    return array;
}

int main(){
    int *a;
    a = make_array_size(20);
    cout << "last index " << a[19] << endl;
    delete[] a;
}

and the errors:

/home/metulburr/Documents/cplusplus/Tutorial/main.cpp||In function ‘int make_array_size(int)’:|
/home/metulburr/Documents/cplusplus/Tutorial/main.cpp|13|error: invalid conversion from ‘int*’ to ‘int’ [-fpermissive]|
/home/metulburr/Documents/cplusplus/Tutorial/main.cpp||In function ‘int main()’:|
/home/metulburr/Documents/cplusplus/Tutorial/main.cpp|18|error: invalid conversion from ‘int’ to ‘int*’ [-fpermissive]|

so i am not really sure what the problem is?




EDIT:
so then i changed it to this:

#include <iostream>
using namespace std;

int make_array_size(int size){
    int *array;
    array = new int[size];

    for (int i=0; i < size; i++){
        cout << "created array[" << i << "]" << endl;
    }
    return *array;
}



int main(){
    int *a;
    *a = make_array_size(20);
    cout << "last index " << a[19] << endl;
    delete[] a;
}

in which executes the function but get a segmentation fault for the main's cout of the array's index?

created array[0]
created array[1]
created array[2]
created array[3]
created array[4]
created array[5]
created array[6]
created array[7]
created array[8]
created array[9]
created array[10]
created array[11]
created array[12]
created array[13]
created array[14]
created array[15]
created array[16]
created array[17]
created array[18]
created array[19]
Segmentation fault

EDIT2:
so then i made a print statement after the function call and before the print of the index of a, in which that didnt print out, so the problem must be wit returning the array back to a? Im just not sure why?

[Athar]

The error is exactly what the error message says. You're returning an int* in your function, but you specified the return type to be int.

[S G H]

Tip: In your last post, the first code is the nearest one.

[metulburr]

ooooooooooh ok i get it, the function also has be *make_array_size(int size)
Iwasnt even thinking about the function header at all for some reason
thanks EssGeEich, that led me to the fix.

[S G H]

Yeah, exactly, that's it! The second code also had a memory leak.