What is the meaning of these keywords used before variables in a
function parameters?
__in__out__in_opt
What is the meaning of these keywords used before variables in a function parameters?
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What is the meaning of these keywords used before variables in a
function parameters?
__in__out__in_opt
Those are some of the older decoration macro’s from Microsoft’s SAL Annotations (the newer ones now follow different casing, starting with a capital, like
_In_,_Out_,_In_opt_). These have no real affect on compilation (under VS 2010 they aren’t even expanded), they are there for inline API documentation.__in: this parameter is an input to the function (read-only, caller initialized).__out: this parameter contains output from the function when it returns (write-only, caller initialized).__in_opt: a compound annotation formed from_inand_opt,_optindications that the parameter is optional and can be set to a default value (generallyNULL).You can get the full explanation here of the older decorations here.