### Question 6.4

Then why are array and pointer declarations interchangeable as function formal parameters?

It's supposed to be a convenience.

Since arrays decay immediately into pointers, an array is never actually passed to a function. Allowing pointer parameters to be declared as arrays is a simply a way of making it look as though the array was being passed--a programmer may wish to emphasize that a parameter is traditionally treated as if it were an array, or that an array (strictly speaking, the address) is traditionally passed. As a convenience, therefore, any parameter declarations which ``look like'' arrays, e.g.

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

are treated by the compiler as if they were pointers, since that is what the function will receive if an array is passed:

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

This conversion holds only within function formal parameter declarations, nowhere else. If the conversion bothers you, avoid it; many people 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.

See also question 6.21.

References: K&R1 Sec. 5.3 p. 95, Sec. A10.1 p. 205
K&R2 Sec. 5.3 p. 100, Sec. A8.6.3 p. 218, Sec. A10.1 p. 226
ANSI Sec. 3.5.4.3, Sec. 3.7.1, Sec. 3.9.6
ISO Sec. 6.5.4.3, Sec. 6.7.1, Sec. 6.9.6
H&S Sec. 9.3 p. 271
CT&P Sec. 3.3 pp. 33-4

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This page by Steve Summit // Copyright 1995 // mail feedback