检测何时多个枚举项映射到相同的值 [英] Detect when multiple enum items map to same value
问题描述
在C/C ++枚举中是否存在编译时检测/防止重复值的方法?
Is there a compile-time way to detect / prevent duplicate values within a C/C++ enumeration?
要注意的是,有多个项目被初始化为显式值.
背景:
我继承了一些C代码,例如:
I've inherited some C code such as the following:
#define BASE1_VAL (5)
#define BASE2_VAL (7)
typedef enum
{
MsgFoo1A = BASE1_VAL, // 5
MsgFoo1B, // 6
MsgFoo1C, // 7
MsgFoo1D, // 8
MsgFoo1E, // 9
MsgFoo2A = BASE2_VAL, // Uh oh! 7 again...
MsgFoo2B // Uh oh! 8 again...
} FOO;
问题在于,随着代码的增长&随着开发人员向MsgFoo1x
组添加更多消息,最终它超出了BASE2_VAL
.
The problem is that as the code grows & as developers add more messages to the MsgFoo1x
group, eventually it overruns BASE2_VAL
.
此代码最终将被迁移到C ++,因此,如果有仅C ++的解决方案(模板魔术?),那是可以的-但与C和C ++一起使用的解决方案更好.
This code will eventually be migrated to C++, so if there is a C++-only solution (template magic?), that's OK -- but a solution that works with C and C++ is better.
推荐答案
有两种方法可以检查此编译时间,但是它们可能并不总是对您有用.首先在MsgFoo2A之前插入标记"枚举值.
There are a couple ways to check this compile time, but they might not always work for you. Start by inserting a "marker" enum value right before MsgFoo2A.
typedef enum
{
MsgFoo1A = BASE1_VAL,
MsgFoo1B,
MsgFoo1C,
MsgFoo1D,
MsgFoo1E,
MARKER_1_DONT_USE, /* Don't use this value, but leave it here. */
MsgFoo2A = BASE2_VAL,
MsgFoo2B
} FOO;
现在,我们需要一种方法来确保在编译时MARKER_1_DONT_USE < BASE2_VAL
.有两种常见的技术.
Now we need a way to ensure that MARKER_1_DONT_USE < BASE2_VAL
at compile-time. There are two common techiques.
声明具有负大小的数组是错误的.这看起来有点难看,但是可以.
It is an error to declare an array with negative size. This looks a little ugly, but it works.
extern int IGNORE_ENUM_CHECK[MARKER_1_DONT_USE > BASE2_VAL ? -1 : 1];
如果MARKER_1_DONT_USE大于BASE_2_VAL,几乎曾经编写的所有编译器都会产生错误.海湾合作委员会吐出:
Almost every compiler ever written will generate an error if MARKER_1_DONT_USE is greater than BASE_2_VAL. GCC spits out:
test.c:16: error: size of array ‘IGNORE_ENUM_CHECK’ is negative
静态断言
如果编译器支持C11,则可以使用_Static_assert
.对C11的支持并不是普遍存在的,但是您的编译器仍然可以支持_Static_assert
,尤其是因为广泛支持C ++中的相应功能.
Static assertions
If your compiler supports C11, you can use _Static_assert
. Support for C11 is not ubiquitous, but your compiler may support _Static_assert
anyway, especially since the corresponding feature in C++ is widely supported.
_Static_assert(MARKER_1_DONT_USE < BASE2_VAL, "Enum values overlap.");
GCC发出以下消息:
GCC spits out the following message:
test.c:16:1: error: static assertion failed: "Enum values overlap."
_Static_assert(MARKER_1_DONT_USE < BASE2_VAL, "Enum values overlap.");
^
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