NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/12430

Text File | 1996-08-05 | 2.0 KB | 86 lines

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: beginner question
Date: Sat, 30 Mar 96 21:13:54 GMT
Organization: none
Message-ID: <[e-mail]>
References: <4jc3sr$[e-mail]> <4jdo7l$[e-mail]> <[e-mail]>
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In article <[e-mail]>
           [e-mail] "Tarang Deshpande" writes:

>Kurt Watzka wrote:
>>
>>   struct FOO
>>   {
>>     int bar;
>>   }
>>
>> FOO is the "struct tag" of that struct, i.e. you can use it to declare
>> variables of that type as in
>>
>>   struct FOO s;
>>
>
>So then what does the following mean:
>
>struct _FOO

I assume you mean 'typedef struct _FOO' here otherwise what you write
below is illegal.

>{
>        int     bar;
>} FOO;
>
>struct _FOO s1;
>FOO         s2;

struct _FOO is a type and is distinct from struct _BAR or struct _BAZ. typedef
is a method for defining aliases for a type. So FOO above is simply an alias
for struct _FOO. So given the definitions above

    FOO  x;

is just another way of writing:

    struct _FOO x;

just as if you write:

    typedef int mytype;

then:

    mytype y;

is just another way of writing:

    int y;

Structure tags are important if you want to create a self-referential
or mutually referential structures e.g.

    struct elem {
        struct elem *next;
        int     value;
    };

You couldn't do this with a typedef because the typedef name wouldn't be
in scope until after the definition i.e. you can't use it within it.

Incidentally avoid identifiers that start with _ ; they are generally
reserved by the language and invoke the undefined behaviour gods when you
use them.

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
-----------------------------------------