Inline initialization of an array

Question

I have this struct:

struct Foo {
    int a;
    int* b;
};

Then I'm creating an instance for it like this:

int x [] = { 5, 6 };
Foo y = { 2, x };

But, I'd like to create the x array inline, maybe something like this:

struct Foo y = { 2, (int[]) { 5, 6 } };

But the example above do not work... How can I achieve this?

--------- EDIT:

I'm getting this error from intellisense:

cast to incomplete array type "int []" is not allowed

Build error:

Error C4576 a parenthesized type followed by an initializer list is a non-standard explicit type conversion syntax

I'm using Visual Studio 2015 (v140).

If you're "creating an instance" like `Foo y = { 2, x };` then there's something missing that you don't show us. There's no type `Foo`. Please create a proper [mcve] to show us. And don't forget to tell us the full and complete error message you get. — Some programmer dude, Jan 29 '19 at 12:02
___Please do not change the question body once an answer is posted. You can always append to it, but changing it completely makes the answer(s) invalid.___ — Sourav Ghosh, Jan 29 '19 at 12:07
You can't `free` the `b` member, because the pointer value was not obtained from `malloc` etc. — Weather Vane, Jan 29 '19 at 12:11

Sourav Ghosh · Accepted Answer · 2019-01-29T12:45:17.933

7

In your case, Foo is not a type.

Try

struct Foo y = { 2, (int[]) { 5, 6 } };

It works as expected

Edit:

You only need to free() the memory programatically which you allocate using the allocator function (malloc() and family). The memory which is not returned by an allocator function, need not be free()-d by the programmer.

Edit 1:

Regarding the C4567, see this

edited Jan 29 '19 at 12:45

answered Jan 29 '19 at 11:58

Sourav Ghosh

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Once you posted your answer, It seems that it works on GCC, but not on Visual Studio. I didn't imagine that this could be a platform problem... – João Paulo Jan 29 '19 at 12:12
1

@JoãoPaulo I was not knowing about visual studio earlier, I evaluated in GCC. – Sourav Ghosh Jan 29 '19 at 12:14
This solution *does* work with MSVC as shown by `printf("%d %d\n", y.b[0], y.b[1]);` – Weather Vane Jan 29 '19 at 12:16
Thanks @WeatherVane sir, I could not see anything in the spec mentioning against it, so I assumed it'd work, but thanks for confirmation. – Sourav Ghosh Jan 29 '19 at 12:17
1

@WeatherVane - MS don't support any C standard past ANSI. How can it work? (Not to fault Sourav, of course, it's MS being annoying). – StoryTeller - Unslander Monica Jan 29 '19 at 12:18
@StoryTeller I did not imagine it. I know it worked because I wrote, compiled and ran a small test program without any warnings, errors or faults. – Weather Vane Jan 29 '19 at 12:19
@WeatherVane - What version of MSVC were you using? What you are saying is news to me – StoryTeller - Unslander Monica Jan 29 '19 at 12:22
@StoryTeller Microsoft (R) Program Maintenance Utility Version 14.00.23506.0. I don't use Visual Studio itself: I do everything with a text editor and a console. – Weather Vane Jan 29 '19 at 12:26
1

@JoãoPaulo C is not C++. C++ is not C. – Lundin Jan 29 '19 at 12:53
@Lundin .. and, `C/C++` is undefined behavior. :) – Sourav Ghosh Jan 29 '19 at 12:54
@Lundin re your deleted answer, I used the compiler from Visual Studio 2015. In OP's original post the keyword `struct` was missing - perhaps that was the problem. Otherwise OP's code was the same as this answer. – Weather Vane Jan 29 '19 at 12:57
2

@JoãoPaulo An initializer list is the whole `= { ... }` thing, which is present in C and C++ both. `(int[]) { 5, 6 }` is a compound literal which is a feature only available in C, not in C++. – Lundin Jan 29 '19 at 12:58
@WeatherVane Apparently the OP compiled C code as C++ and then compound literals aren't available. – Lundin Jan 29 '19 at 12:58

Inline initialization of an array

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