CODEWITHSUNDEEP
c++pointers
bev
bev

Reputation: 187

Having trouble using an array that is returned by a function in C++

I have a function that generates values in an array and returns a pointer to that array. Here's the MWE code:

int *f(size_t s)
{
    int *ret=new int[s];
    for(size_t a=0;a<s;a++)
    {
    ret[a]=a;
    cout << ret[a] << endl;
    }
    return ret;
}

note that I have a cout line in for for loop to prove to myself that the array is being populated properly.

Now, here's my problem. I can't find the correct method of using the returned array. Here's what I've been doing:

int main (void)
{
 int ary_siz = 10;
 int ary[ary_siz];
 *ary = *f(ary_siz);
 cout << ary[0] << endl;
 cout << ary[2] << endl;
 cout << ary[3] << endl;
}

The first element in ary seems to be right. The others (ary[1],ary[2]...) are not. Can anyone tell me what I'm doing wrong?

Upvotes: 0

Views: 76

Answers (4)

akappa
akappa

Reputation: 10490

You allocate an array in the function and you just assign its first element to the first element of your stack-allocated array, instead of just using the returned array.

you should do something like that:

int main (void)
{
 int ary_siz = 10;
 int *ary;
 ary = f(ary_siz);
 cout << ary[0] << endl;
 cout << ary[2] << endl;
 cout << ary[3] << endl;
 delete[] ary // don't forget to release the memory
 return 0; // You should return something in the main function
}

Moreover, in C++ you should use vectors instead of "bare-metal" arrays whenever possible.

Upvotes: 1

user142019
user142019

Reputation:

How about this?

int *ary = f(ary_siz);

The you can just use the [] operator as you do in the couts.

Upvotes: 0

sehe
sehe

Reputation: 392999

The assignment 

*ary = *f(ary_siz);

copies a single element. Use

int main (void)
{
 int ary_siz = 10;
 int *ary = f(ary_siz);

 delete[] ary;
}

fixing the memory leak as well

Upvotes: 1

Vaughn Cato
Vaughn Cato

Reputation: 64308

int main (void)
{
 int ary_siz = 10;
 int *ary = f(ary_siz);
 cout << ary[0] << endl;
 cout << ary[2] << endl;
 cout << ary[3] << endl;
 delete [] ary;
}

Upvotes: 4

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