How to use enums in C safely?

Question

consider the following example:

typedef enum {Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday} Day; void DoSomething(Day day){ //some code }

The problem is that the following code complies: DoSomething(74). So how can I check in DoSomething that my parameter is really a Day? (relying on numbers won't work because if I change my enum like that Sunday=7 .... ,I want it to work too, and checking if(day==Sunday || day ==...) looks inefficient).

enum in C++11 are type-safe.stackoverflow.com/a/12581154/1809377 — ajay
– ajay, Commented Apr 4, 2014 at 9:53

user541686 · Accepted Answer · 2014-04-04 09:45:12Z

5

The short answer is you can't.

The long answer is you can try to put a "minimum" and a "maximum" member, and check that the value falls in the range between the two... or some other similar trick.

answered Apr 4, 2014 at 9:45

user541686

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2 Comments

Michael Over a year ago

But if you check day >=0 && day <=6 and then change your enum to Sunday=7... , your code won't works.

user541686 Over a year ago

@Sefi: You would do enum {First,Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Last} Day; and then check if First < day && day < Last.

A.B. · Accepted Answer · 2014-04-04 09:55:30Z

1

typedef enum {Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday, Last} Day; void DoSomething(Day day){ // if day < Last ... }

edited Apr 4, 2014 at 9:55

answered Apr 4, 2014 at 9:45

A.B.

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1 Comment

unwind Over a year ago

If you're going to go this route, I think it's much better to just have Last (without an assignment) and then check using day < last, since that makes the construct less brittle. Otherwise you can add something after Saturday and fail to update Last, causing breakage.

Sergi Pasoevi · Accepted Answer · 2014-04-04 09:46:31Z

You could put a switch statement in your DoSomething.

switch(day){ case Day.Monday: // something break ... default: // ignore or something

Vicky · Accepted Answer · 2014-04-09 07:47:33Z

If you write DoSomething(74) statement in your code modern compiler generate warning saying DoSomething expect enum but integer is passed.

But if you are passing a value from user input where any value can be passed to DoSomething() then you will have to take care as other advised.

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