I'm trying to find an answer to a seemingly straightforward question, but it is proving more difficult than I thought it would.
The question is: if I create an array of pointers, using unsafe code in C#, will the elements of the array all be initialized to null? The documentation in the C# spec initially seems clear: section 12.2 'Array creation' says that elements of arrays created by array-creation-expressions are always initialized to their default value. But section 5.2 'Default values' only defines the default values for value types and reference types. Section A.2 'Pointer types' makes it clear that pointer-type is different from either value-type or reference-type, so the information in 5.2 presumably doesn't apply here, since it only talks about pointer-type and reference-type. I can't actually find anything that says what the default value for a pointer-type would be. So the provisional conclusion I reached from the C# spec is that if I create an array of pointers, the value of the elements is undefined (because there is no definition that tells us what the default value for a pointer-type is). So if I want the array to start off full of nulls, I'm actually going to have to loop through and fill it with nulls. This seems kind of surprising, since you don't normally have to initialize arrays. But I guess in an unsafe context, fewer things are guaranteed for you. Moreover, Serge Lidin's "Inside Microsoft .NET IL Assembler" says of the 'newarr' instruction that the newly created array is always zero-initialized. It doesn't mention any exceptions. (At least not on any of the pages listed for 'newarr' in the index...) Partition III of the CLI spec is a little less clear. In section 4.19, it says that when newarr is used to create a zero-based one-dimensional array of numbers, that the elements of the array will be initialized to 0. It also says that non-zero-based or multi-dimensional arrays don't use newarr. Unfortunately it doesn't say what happens with zero-based one-dimensional arrays of anything other than numbers, which is a shame, since the C# compiler uses newarr when creating a new array of pointers. Empirically, I get all nulls when creating a new array of pointers. But my reading of the specs indicates that this is not something that I can rely on, because the official behaviour appears to be undefined. Did I miss anything in the documentation that clears this up? -- Ian Griffiths DevelopMentor =================================== This list is hosted by DevelopMentorŪ http://www.develop.com NEW! ASP.NET courses you may be interested in: 2 Days of ASP.NET, 29 Sept 2003, in Redmond http://www.develop.com/courses/2daspdotnet Guerrilla ASP.NET, 13 Oct 2003, in Boston http://www.develop.com/courses/gaspdotnet View archives and manage your subscription(s) at http://discuss.develop.com
