Warning: Cannot initialize enumeration with an integer.

Question

I've found some inconsistent behavior in the CC compiler related to assigning ints to an enum.
Compile this code:
// Compiled with:
// CC: Sun WorkShop 6 update 2 C++ 5.3 Patch 111685-13 2003/02/04
enum chairs {bluechair=0, greenchair=1, redchair=2};
enum walls {bluewall, greenwall, redwall};
typedef enum walls walls;
int main ()
walls mywall = 0; // Error: Cannot use int to initialize walls.
mywall = 0; // Error: Cannot assign int to walls.
walls mywalls[]={
bluewall, // OK
(walls) 0, // OK
(walls) bluechair, // OK
(int) 0, // Error: Cannot use int to initialize walls.
(int) bluechair, // Error: Cannot use int to initialize walls.
static_cast<int> (0), // Error: Cannot use int to initialize walls.
static_cast<int>(bluechair), // Error: Cannot use int to initialize walls.
0 // Warning: Cannot initialize enumeration with an integer.
mywalls[1] = 0; // Error: Cannot assign int to walls.
return 0;
When compiled with g++ and gcc all I get is the same warning:
chairsandwalls.cc:16: warning: conversion from `int' to `enum walls'
Should it all be Errors or Warnings?
Is there some reason why this might actually be the expected behavior?
Diego.

Answer 1

Integral to enumeration is not a standard conversion as specified in section 4 (Standard conversions) of the C++ standard. You need to cast any such conversion. The GNU compiler is more lax on this point than WorkShop/Studio, and only generates a warning.
The reason this is an error has to do with type-safety -- an enumeration has a limited set of valid values, and the language forces you to cast when assigning from an integer saying, "Yes, this is a valid value."