C language Annotation function parameter description:

Input parameters are parameters used to pass data into a function.
The output parameter is the parameter that passes the result of the function out to the program block of the calling statement.

An output parameter is a parameter of a function that is written in parentheses after the function name. The return value is the value returned by the return statement in the function and sent to the expression in the calling statement.

eg

RECVBUF is the output parameter of the Recvfrom, save the received content, do not initialize.
SENDBUF is the input parameter of the SendTo, the contents of the deposit, to initialize.

C language Annotation function parameter description: