Access enum entries from anonymous struct

Question

I've a code like this:

struct
{
    enum
    {
        entry,
    } en;

} data;

void foo()
{
    switch(data.en)
    {
    }
}

that gives me a warning:

main.cpp:13:11: warning: enumeration value 'entry' not handled in switch [-Wswitch]

     switch(data.en)

which is expected. I'm curious if I can add case entry: without making my struct named one (which obviously works).

This:

struct
{
    enum
    {
        entry,
    } en;

} data;

void foo()
{
    switch(data.en)
    {
        case entry:
        break;
    }
}

gives an error + warning:

main.cpp: In function 'void foo()':

main.cpp:15:14: error: 'entry' was not declared in this scope

         case entry:

              ^~~~~

main.cpp:13:11: warning: enumeration value 'entry' not handled in switch [-Wswitch]

     switch(data.en)

           ^

@EOF - _I'm curious if I can add case entry: without making my struct named one_ — ryyker, May 15 '17 at 22:04
The `case entry:` code works for me **when compiling as C rather than C++**. — EOF, May 15 '17 at 22:07

score 3 · Answer 1 · answered May 15 '17 at 22:29

3

You can write:

case decltype(data.en)::entry:

however I think it would not be considered good code.

answered May 15 '17 at 22:29

M.M

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This looks awful :) And a tad funny – Passer By May 16 '17 at 05:44
Interesting solution :) Thx – Michał Walenciak May 16 '17 at 17:27

score 1 · Accepted Answer · answered May 15 '17 at 22:36

In C you can do it the following way

#include <stdio.h>

struct
{
    enum
    {
        entry,
    } en;

} data = { entry };

void foo()
{
    switch ( data.en )
    {
        case entry:
            puts( "Hello, World!" );
            break;
    }
}

int main( void )
{
    foo();
}

In C++ you do it the following way

#include <iostream>

struct
{
    enum
    {
        entry,
    } en;

} data = { decltype( data.en )::entry };

void foo()
{
    switch ( data.en )
    {
        case data.entry:
            std::cout <<  "Hello, World!" << std::endl;
            break;
    }
}

int main()
{
    foo();
}

That's nice. Looks a little bit odd at first glance, but it's quite reasonable. — Michał Walenciak, May 16 '17 at 17:26

Access enum entries from anonymous struct

2 Answers2