What is the difference between the parameters type COM ATL function [in] [out] [in/out] [retval] [out/retval] ?

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I think retval is used to return a value to the user & in is for input. But i cant differentiate between out & retval. I have gone through several articles but not able to understand it. can anyone explain it for me?

Posted 11-Aug-15 20:50pm

Somesh Dhal

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Solution 1

hi,
check out these links :
stackoverflow questions[^]

MSDN links::
link 1[^]
link 2[^]

hope this helps !!

Posted 11-Aug-15 23:53pm

chandanadhikari

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Philippe Mori · Accepted Answer · 2015-08-12T06:42:00

If you code in C/C++ without using any wrapper stuff, then both out and retval would have the same effect.

If you generate wrappers or use other langages, then one argument would become the return vale of the function.

C++

HRESULT Test([out, retval] int *rv) { ... }

would become

C++

int Test() { ... }

and throw an exception in case of an error (negative HRESULT).