Initializing array of structs within an array of structs

Question

Given the following code:

struct BufferPair
{
    ByteBuffer _a;
    ByteBuffer _b;

    bool _c;
};

struct TestData
{
    MyClass _myClass;

    BufferPair _data[];
};

I'm trying to initialize an array of TestData where I also initialize an array of BufferPair. Each instance of TestData will have a differently sized BufferPair array. Simplified Example:

const TestData g_Data[] = { MyClass(), { { bufOne, bufTwo, someBool }, { bufThree, bufFour, anotherBool } } };

While trying this, I get the following gcc error:

error: too many initializers for 'BufferPair [0]'.

How would I solve this? Thanks.

score 2 · Accepted Answer · edited Jun 20 '20 at 09:12

2

struct TestData
{
    MyClass _myClass;
    BufferPair _data[];
};

_data in the code above is not a complete type (it is lacking the size of the array), and you are not allowed to declare a member to be of incomplete type in the C++ standard:

9.2p10

Non-static (9.4) data members shall not have incomplete types.

This seems to compile as an extension to the language in gcc. Now it still fails to compile the definition of the variable as the array has no size and you are trying to initialize members in it.

edited Jun 20 '20 at 09:12

Community

1
1

answered Apr 20 '12 at 13:27

David Rodríguez - dribeas

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Curious. Which extension allows for this? – MarkP Apr 20 '12 at 13:51
@MarkP: Searching for `gcc array member size` I found [this](http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html) which is an extension for C, which might also be available in C++... but at any rate, in C++ you should avoid using it, since it is not standard. – David Rodríguez - dribeas Apr 20 '12 at 13:58

score 1 · Answer 2 · answered Apr 20 '12 at 13:26

1

You didn't write the size of the array BufferPair[] - it's zero, so you can't fill it with values.

Try BufferPair[2] and see if this solves the problem.

answered Apr 20 '12 at 13:26

Israel Unterman

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score 0 · Answer 3 · edited May 23 '17 at 12:03

0

You cannot initialize an array without a length, as said in the other answers. The only way to do this is initializing the struct at runtime using the "Length 1 trick" (or length 0 trick if you're using gcc).

See this post for more information on how to do that Allocating struct with variable length array member

edited May 23 '17 at 12:03

Community

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answered Apr 20 '12 at 13:31

Erwin B.

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Initializing array of structs within an array of structs

3 Answers3