Array of zero length

Question

I am working on refactoring some old code and have found few structs containing zero length arrays (below). Warnings depressed by pragma, of course, but I've failed to create by "new" structures containing such structures (error 2233). Array 'byData' used as pointer, but why not to use pointer instead? or array of length 1? And of course, no comments were added to make me enjoy the process... Any causes to use such thing? Any advice in refactoring those?

struct someData
{
   int nData;
   BYTE byData[0];
}

NB It's C++, Windows XP, VS 2003

Answer 1

This is an old C hack to allow a flexible sized arrays.

In C99 standard this is not neccessary as it supports the arr[] syntax.

Answer 2

There are, unfortunately, several reasons why you would declare a zero length array at the end of a structure. It essentially gives you the ability to have a variable length structure returned from an API.

Raymond Chen did an excellent blog post on the subject. I suggest you take a look at this post because it likely contains the answer you want.

Note in his post, it deals with arrays of size 1 instead of 0. This is the case because zero length arrays are a more recent entry into the standards. His post should still apply to your problem.

http://blogs.msdn.com/oldnewthing/archive/2004/08/26/220873.aspx

Answer 3

Yes this is a C-Hack.
To create an array of any length:

someData mallocSomeData(int size)
{
    someData*  result = (someData*)malloc(sizeof(someData) + size * sizeof(BYTE));
    if (result)
    {    result->nData = size;
    }
    return result;
}

Now you have an object of someData with an array of a specified length.