Tuesday, February 10, 2009

C array name vs variables, again

(This applies to C/C++, but how about c# and java? I guess this is an obscure grammar rule that many people just follow without investigating.)

An array name looks like a ptr variable but no no no. Analogue -- an array object is a (permanently) allocated "room" in memory; an array name is a (permanent and dominant) name plate on the room door, which a variable never is.

Rule1: Suppose an array name is "myArray", you can't put this "myArray" name plate on another room's door later on.

Rule2: You can't put another name plate ("myArray2") on the same door.

This array name is a permanent and exclusive "owner" of this particular room. Conversely, the room permanently belongs to this array name. An "aliasing" pointer Variable can be created for this same address, but compiler won't allow another array-name as another name plate on this room (Rule2)

Before Variable-Length-Array, array size must be determined at compile time, therefore for a function f(int pa[]), the array-name pa is nonsense. Actually, the compiler translates that to f(int* pa). VLA didn't change this rule.

See [[c++ primer]].

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