c++ - Significance of __IN__ and __OUT__ qualifiers for parameters in ODBC API's Signature -

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• what purpose of __in __out __in_opt __allowed(), how work? should use similar constructs in own code? 4 answers

reading through microsoft implementation of odbc header file sql.h, parameters of declarations of apis qualified __in__ or __out__.

example

sqlreturn  sql_api sqlrowcount(_in_ sqlhstmt statementhandle,                                _out_ sqllen* rowcount); 

i understand, such usage used determined direction transport optimization particularly used in com world data needs marshaled , un-marshalled such usage seems odd in odbc context.

what significance of these qualifiers odbc perspective?

syntactically, there no significance @ all. both #defined nothing someplace. they're helping make api more readable in isolation documentation - marking parameters inputs function , outputs.