[StructLayout(LayoutKind.Sequential)]

[3bood ghzawi]

Hi all, i counter this statment at some code, but i don't undestand what means, so, i need helping of what it means in detail... [StructLayout(LayoutKind.Sequential)] Thanks......

[Luc Pattyn]

Maybe this[^] helps. If not, ask more specific questions, with context and purpose. :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

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I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.

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[0x3c0]

Normally the compiler pads structures out so that it can use optimised four-byte transfer operations. But different compilers do that in different ways. LayoutKind.Sequential lays the structure out exactly as you specify, not how the compiler thinks will run well. It's commonly used in PInvoke, because C# and C compilers are likely to pad things out differently.

OSDev :)

[dan sh]

Believe it or not, MSDN is your friend. Search it.

50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong...!!

[Lost User]

If you don't specify it, the compiler would be free to sort the fields by size so as to minimize padding.

[DaveyM69]

It's commonly used when using external C/C++ dlls (PInvoke). When a structure is being passed as a parameter to an external function then the called C/C++ function needs to know exactly where to find the relavent parts of the structure in memory. It does this using byte offsets from the start address (pointer) of the struct. Imagine you had this structure

public struct MyStruct
{
public byte a;
public int b;
}

Without specifying the LayoutKind, this could end up being layed out in memory with b first. This would be catastrophic for the external function as it would assume the fields to be layed out in sequence - so with a first. As a result the data retrieved from memory would be incorrect. To make sure that the sequence of fields is preserved, we use LayoutKind.Sequential. Another common one is LayoutKind.Explicit (most commonly when used with C/C++ unions). Here you explicitly state the offset for each field using the FieldOffset attribute.

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
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