How to delete 1D array

Question

I create an array like as below

int size = 5;
double my_arr[m_size];

for (int i = 0; i < size; i++)
{
    my_arr[i] = (rand()%10+1) +  ((double) rand() / (RAND_MAX));;
}

after doing some calculation on array I want to delete the array. So I do this

for (int i = 0; i < size; i++)
    {
       delete my_arr[i]; 
    }

and I get this error

error: type ‘double’ argument given to ‘delete’, expected pointer

I searched internet and all solutions are related to pointer array. But I am not using any pointer. So how can I delete this array?

You don't. It's automatically deleted when the stack rewinds and the variable goes out of scope. — tkausl, Jun 22 '16 at 15:35
Reminder: `new` and `delete` are a pair. When you use `new` to allocate, use `delete` when finished. — Thomas Matthews, Jun 22 '16 at 15:38
you dont need to worry about deleting variables that is putted on stack — Lorence Hernandez, Jun 22 '16 at 15:40

score 3 · Answer 1 · edited Jun 22 '16 at 16:08

The array will be automatically deleted when leaving the scope in which the variable has been declared. If you really need to free memory fast you can try put your code between embraces:

{ //create new scope
    int size = 5;
    double my_arr[m_size];

    for (int i = 0; i < size; i++)
    {
        my_arr[i] = (rand()%10+1) +  ((double) rand() / (RAND_MAX));;
    }

    //some stuff

} //all non-pointer objects (or arrays) will be deleted

Or you can use pointers :

double *pMyarr =  new double[m_size] ;

Lorèloi · Answer 2 · 2016-06-23T09:06:53.707

First of all, I think you should consider using a memory leak detector in your programms, so you can know by yourself if your code is leaking and if you have to do something about it. In your code you would have seen that there is no need to delete anything. :)

As far as I know, you should worry about memory in only two cases:

You have allocated a C-style array with malloc or calloc. In this case, you need to use the function free to deallocate the array. But generally in C++, you don't want this. You prefer using a container like std::array or std::vector instead.
You have created a new instance of an class with new and you have got a pointer to this instance. In this case, you have to use delete on the pointer when you don't need this instance anymore. But generally in C++11 (or further), you don't want this. If you really have to use a pointer, you prefer creating a smart pointer like std::unique_ptr or std::shared_ptr which will handle the memory for you.

When you define a variable without using new, malloc or calloc, (for example int a = 1 ;), it will be automatically deleted when it goes out of scope. So you don't need to worry.

Here is a simple example of a variable going out of scope:

int a = 1 ;
{
    int b = 1 ;

    // b is implictly deleted here, just before the bracket.
}
a++; // It works, because a exists in this scope
b++; // It doesn't work, because b is out of scope.

// a is implicitly deleted here, assuming we are at the end of a function

An extra guideline for the second bullet point would be "But generally in C++, you don't want this. You prefer using `std::make_unique` and `std::make_shared` (or `std::array` and `std::vector` like the previous item)" — KABoissonneault, Jun 22 '16 at 16:50
@KABoissonneault ; I didn't know about the functions `make_unique` and `make_shared` (Partly because I'm stuck to C++11). But you make a good point by mentionning smart pointers. I'll edit my answer. I just wonder; `std::make_unique("hello")` has the same purpose as `std::unique_ptr(new string("hello"))`, doesn't it ? — Lorèloi, Jun 23 '16 at 08:47
@Lorèloi there is a stronger protection against memory-leaks in some cases, see http://stackoverflow.com/questions/22571202/differences-between-stdmake-unique-and-stdunique-ptr — tkausl, Jun 23 '16 at 14:44

How to delete 1D array

2 Answers2