为什么没有/限制检查枚举值？ [英] Why no/limited checking on enum values ?
问题描述
考虑
enum Side {Back，Front，Top，Bottom};
enum side a;
现在，为什么
a = 124;
合法（好吧它真的是一个整数，但仍然，
检查可以执行..）？
如果
更多的类型检查会不会更有用？
< BLOCKQUOTE>"星云" <无**** @ example.com>在留言新闻中写道：41 ****** @ news.wineasy.se ...
考虑
枚举边{Back，Front，Top，Bottom};
enum side a;
现在，为什么
a = 124;
合法（好吧它真的是一个整数，但仍然可以进行检查......）？如果有更多的类型检查，那么枚举会不会更有用吗？
枚举类型是int的符号名称。声明
enum边a;
只是声明''a''为int。
Nebula< no **** @ example.com>写道：
考虑
枚举边{Back，Front，Top，Bottom};
enum Side a;
现在，为什么
a = 124;
合法（它确实是一个整数，但仍然可以执行检查......）？
如果有一个<更多的类型检查？
好问题。它永远不是非法的，AFAIK;根据这两个标准，它肯定合法
。最初的原因可能是它不是
总是可以在编译时进行检查，导致运行时间
检查C中总是有的认为（并非没有理由）因为b $ b太昂贵了。有一种解决方法是通过制作枚举_not_
真的是一个整数，但这可能会使一些现有的程序无效，这是标准委员会的事情。
总是（可以说是太）谨慎行事。
Richard
Nebula写道：考虑
枚举边{Back，Front，Top，Bottom};
enum Side a;
现在，为什么
a = 124; <合法（好吧它确实是一个整数，但仍然可以执行检查......）？
如果有更多的类型检查，那么就不会有更有用的功能？
enum既不是一个集合也不是列表。
枚举工具是一个{方便}的方法来
将数字与符号相关联。没有更多
没有更少。
工厂不强制要求任何关系
amoung标识符。没有要求
每个标识符在枚举中具有唯一值。
语法允许关联
a枚举的名称（标识符）。
以下枚举说明了这一点：
enum废话
{Moon = 5，Sun = 73，West = 4，Cake = 41623};
enum是的{one，two，frog，skip，my，lou};
/ *请注意，符号一将* /
/ *与零值相关联。 * /
枚举不应被视为一种类型。
如果你想让枚举单独使用
类型，例如Pascal中的RECORD，然后你必须创建一个。
许多编程商店禁止使用enum工具。
他们更喜欢使用#define。
许多错误都是通过在枚举应该是什么（设置，列表等）上设置假设
来做出的。 ）
而不是它实际上是什么。
-
托马斯马修斯
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Consider
enum Side {Back,Front,Top,Bottom};
enum Side a;
Now, why is
a = 124;
legal (well it really is an integer, but still,
checking could be performed..) ?
Wouldn''t enums be more useful if there was a
bit more typechecking ?
"Nebula" <no****@example.com> wrote in message news:41******@news.wineasy.se...Consider
enum Side {Back,Front,Top,Bottom};
enum Side a;
Now, why is
a = 124;
legal (well it really is an integer, but still,
checking could be performed..) ?
Wouldn''t enums be more useful if there was a
bit more typechecking ?
An enum type is a symbolic name for an int. Declaring
enum Side a;
is simply declaring ''a'' to be an int.
Nebula <no****@example.com> wrote:
Consider
enum Side {Back,Front,Top,Bottom};
enum Side a;
Now, why is
a = 124;
legal (well it really is an integer, but still,
checking could be performed..) ?
Wouldn''t enums be more useful if there was a
bit more typechecking ?
Good question. It never has been illegal, AFAIK; it''s certainly legal
under both Standards. The original reason probably is that it''s not
always possible to do this checking at compile-time, leading to run-time
checks which have in C always been regarded (not without reason) as
being too costly. There''s a way around that by making enums _not_ be
really an integer under the hood, but that would probably invalidate
some existing programs, which is something the Standard Committee has
always been (arguably too) wary of doing.
Richard
Nebula wrote:Consider
enum Side {Back,Front,Top,Bottom};
enum Side a;
Now, why is
a = 124;
legal (well it really is an integer, but still,
checking could be performed..) ?
Wouldn''t enums be more useful if there was a
bit more typechecking ?
The enum is neither a set nor a list.
The enum facility is a {convenient} method to
associate numbers with symbols. Nothing more
nothing less.
The facility does not mandate any relationship
amoung the identifiers. There is no requirement
that each identifier have a unique value within
the enum.
The syntax allows one to associate
a name (identifier) to an enum.
The following enums illustrates the point:
enum Nonsense
{Moon = 5, Sun = 73, West = 4, Cake = 41623};
enum Yep {one, two, frog, skip, my, lou};
/* Note that the symbol ''one'' will associate */
/* with the value of zero. */
An enum should not be considered as a type.
If you want the enum to be have as a separate
type, such as the RECORD in Pascal, then you
must create one.
Many programming shops ban the enum facility.
They prefer to use #define instead.
Many mistakes are made by placing assumptions
on what an enum should be (set, list, etc.)
rather than what it actually is.
--
Thomas Matthews
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