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Editorial Team
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Asked: 2026-06-09T12:29:42+00:00

I am trying to do some work on Windows drivers but I am having

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I am trying to do some work on Windows drivers but I am having trouble understanding one part of the example source code. I have never seen this before in my C experience and I couldn’t find anything on it. Anyways, I was wondering what the “IN” part of the parameter variables are? Below is an example of the header of a function. It is also possible for it to be a few other things like “OUT”, “INOUT”, “INOPT”, and maybe more (couldn’t find anything else). 

VOID
PLxReadRequestComplete(
    IN WDFDMATRANSACTION  DmaTransaction,
    IN NTSTATUS           Status
    )
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  1. Editorial Team

    Those are simply markers (from the early days of the Windows DDK) that describe the intended use of the parameter.

    In normal builds the macros are defined as nothing, however they could conceivably be defined to implementation-specific keywords that allow the compiler (using SAL or other static code analysis tools) to perform deeper analysis about the correct use of the argument/parameter. I don’t think that they’re used for SAL because they simply aren’t ‘rich’ enough to describe all the attributes that SAL likes to take into account. So I think they’re mainly intended to communicate intent to programmers.

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