Sending fewer parameters then arguments

Hi, I want to write a function that takes in 3 arguments of type char*, but when I call this function from other functions I only want to pass in 1 parameter.
So below shows my function and I want its first argument to come from one function, the second to come from another function and the third from a different function.

Code:

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void Output(char*, char*, char*) {

}

Output(Chat_room, ?, ?);


Output( ?, user, ?);


Output( ?, ?, Time);

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each call comes from other functions. Does anyone know how I can achieve this?

Code:

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Output(GetChatRoom(), GetUser(), GetTime())

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maybe?