comp.lang.c FAQ list · Question 6.4

Q: If they're so different, then why are array and pointer declarations interchangeable as function formal parameters?

A: It's supposed to be a convenience.

Since arrays decay immediately into pointers, an array is never actually passed to a function. You can pretend that a function receives an array as a parameter, and illustrate it by declaring the corresponding parameter as an array:

	void f(char a[])
	{ ... }

Interpreted literally, this declaration would have no use, so the compiler turns around and pretends that you'd written a pointer declaration, since that's what the function will in fact receive:

	void f(char *a)
	{ ... }

There's nothing particularly wrong with talking about a function as if it ``receives'' an array, if the function is traditionally used to operate on arrays, or if the parameter is naturally treated within the function as an array.

This conversion of array-like declarators into pointers holds only within function formal parameter declarations, nowhere else. If the conversion bothers you, you're under no compulsion to make use of it; many programmers have concluded that the confusion it causes outweighs the small advantage of having the declaration ``look like'' the call or the uses within the function. (Note that the conversion happens only once; something like char a2[][] won't work. See questions 6.18 and 6.19.)