Returning new array

Why does compiler complain:
warning: address of local variable 'newList' returned

I thought we could return values b/c in fact we are returning a copy of it.

Code:

---

int* newList(int* list, int size)
{
 int newSize = size * 2;
 int newList[] = {};
 
 for ( int i = 0; i < newSize; ++i )
  list[i] = 0;
 
 return newList;
}

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a couple things:

no, you'd return a copy of the integer address of where newList used to be (it's probably just been cleaned off the stack when the function exits).

you're returning an empty array.

you're also going to walk off the end of list in your for loop there

avoid newing in a function without a thoroughly thought-out memory management model.

I mean:

Code:

---

int* newList(int* list, int size)
{
 int newSize = size * 2;
 int newList[] = {};
 
 for ( int i = 0; i < newSize; ++i )
  newList[i] = 0;

 
 return newList;
}

---

What do you mean I should avoid newing within a function?

it complains because the returned pointer would point to a freed resource after the function completes. For all intent, the pointer is invalid.

Now you're just invoking undefined behavior. The size of newList isn't newSize.
Initializing an array with an empty initializer list shouldn't even compile.
You are better off learning how to use std::vector instead.

Quote:

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Originally Posted by Elysia

Initializing an array with an empty initializer list shouldn't even compile.

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It does, but you know, if you do something else wrong, you break everything.

It doesn't compile for me:
error C2466: cannot allocate an array of constant size 0

Make the size greater than zero (duh).

Ah, well, perhaps you misunderstood my intent.
Initializing an array without an explicit size and an empty initializer list will compile. This is exactly what the OP did and what I was complaining about.

I can only read what you take the time to type, you know.

Yes you're right that I should learn libraries such as C++'s STL w/ vectors, but as a new programmer I thought I learn the basics and I thought creating a new array would be one of those 'basics'.

There are different kinds of arrays.
If you want a static array, learn std::array.
If you want a dynamic array, learn std::vector.
There is little need for C-style arrays unless you need to work with C code (or have an outdated compiler).
Those are basics. You'll save a lot of time with these instead of having to learn how to dynamically manage memory in order to resize your arrays.

Quote:

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Originally Posted by monkey_c_monkey

Yes you're right that I should learn libraries such as C++'s STL w/ vectors, but as a new programmer I thought I learn the basics and I thought creating a new array would be one of those 'basics'.

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C arrays aren't the basics. They are the backwards compatibility features.