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Re: Warning: format '%i' expects type 'int *', but argument 2 has type 'enum month *'

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James Kuyper <jameskuyper@verizon.net> writes:
> On 11/07/2015 11:24 AM, Alla _ wrote:
>> Here is a simple program from the book. When I compile it, the compiler
>> generates a warning addressing it to the part with scanf(): 
>> 
>> warning: format '%i' expects type 'int *', but argument 2 has type 
>> 'enum month *'
[...]
>>     enum month {January = 1, February, March, April, May, June, July, August, September, October, November, December};
>>     enum month a_month;
>>     
>>     int days;
>>     
>>     printf("Enter month number:  ");
>>     scanf("%i", &a_month);
[...]
>> Obviously, authors of the book didn't get that warning, or ignored it.
>> I understand that I am asking for an integer, the number of a month, hence
>> type int %i; but asking scanf to put that value into enum month. I know
>> that enumeration values (names in curly braces) are treated by compiler
>> as integers. But the variable a_month has the 'enum month' type.
>
> Correct. "Each enumerated type shall be compatible with char, a signed
> integer type, or an unsigned integer type. The choice of type is
> implementation-defined,128) but shall be capable of representing the
> values of all the members of the enumeration." (6.7.2.2p4). Note, in
> particular, that "enum month" need not be compatible with 'int'. The
> compatible type could easily be "unsigned char" in this case.
>
>> Is there a way to avoid such warning without altering the program's
>> simplicity?
>
> Yes. Declare a_month to have the type 'int' rather than "enum month".

Or you can read into a temporary int variable, and copy its value to
a_month:

    int month_number;
    int result = scanf("%d", &month_number);
    if (result == 1) {
        a_month = month_number;
    }
    else {
        /* error handing */
    }

Note that I've changed the format from "%i" (which accepts decimal,
octal, or hexadecimal input) to "%d" (which accepts decimal input).  If
the user enters "09", presumably you want to treat it as 9, not as an
error.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Warning: format '%i' expects type 'int *', but argument 2 has type 'enum month *' Alla _ <modelling.data@gmail.com> - 2015-11-07 08:24 -0800
  Re: Warning: format '%i' expects type 'int *', but argument 2 has type 'enum month *' James Kuyper <jameskuyper@verizon.net> - 2015-11-07 11:52 -0500
    Re: Warning: format '%i' expects type 'int *', but argument 2 has type 'enum month *' Keith Thompson <kst-u@mib.org> - 2015-11-07 13:42 -0800
  Re: Warning: format '%i' expects type 'int *', but argument 2 has type 'enum month *' Barry Schwarz <schwarzb@dqel.com> - 2015-11-07 16:45 -0800

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