CODEWITHSUNDEEP
c
btse
btse

Reputation: 8021

What is this IN part of the parameter to a function?

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
    )

Upvotes: 2

Views: 88

Answers (2)

Michael Burr
Michael Burr

Reputation: 340218

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.

Upvotes: 5

Ernest Friedman-Hill
Ernest Friedman-Hill

Reputation: 81694

That's not standard C. Most likely, IN has been defined to have some other value using a #define -- i.e., a macro. Search your *.h files for #define IN, #define OUT, etc, and see if you can find out what.

Upvotes: 2

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