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Inside linux kernel sources i see that, inside enums, is there also a define with the same name of enum element. Example in linux/rtnetlink.h we have:
enum {
RTM_BASE = 16,
#define RTM_BASE RTM_BASE
RTM_NEWLINK = 16,
#define RTM_NEWLINK RTM_NEWLINK
RTM_DELLINK,
#define RTM_DELLINK RTM_DELLINK
...
What is the reason for this? I can't figure out how this is used.
Thanks
685
Two enum names can have same value. For example, in the following C program both 'Failed' and 'Freezed' have same value 0.
We can an enumeration inside a class. But, we cannot define an enum inside a method.
There is currently no way to detect or prevent multiple identical enum values in an enum.
The values assigned to the enum names must be integral constant, i.e., it should not be of other types such string, float, etc. All the enum names must be unique in their scope, i.e., if we define two enum having same scope, then these two enums should have different enum names otherwise compiler will throw an error.
One thing I could think of is that you can check for the very existence of the enum by means of the macro:
#ifdef RTM_BASE
int flag = RTMBASE;
#else
int flag = 0;
#endif
No idea if that's what's going on, though.
131
Another thing these #defines achieve, besides allowing old code to continue the old names should the enum constant names be changed, and checking whether they are defined, is to prevent other code to define these symbols.
#include <linux/rtnetlink.h>
// for some reason, the author thinks
#define RTM_BASE 17.3f
// is a good idea
would not compile.
32
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