I'm having trouble understanding how the following code maps to the
syntax specified in ISO/IEC 14882:2003.

typedef union {
.
      struct str_pair_t drive;
.
} yystype;

(The ellipses respresent suppression of detail superfluous to this
discussion.)


This is in the form

typedef type-specifier yystype;

and I'm having no problem with that part.


Therefore,

union {
.
      struct str_pair_t drive;
.
}

is a type-specifier, specifically a class-specifier.


 From Clause 9,

class-specifier:

    class-head { member-specification_opt }



Therefore,

.
      struct str_pair_t drive;
.

is a member-specification.


We match Clause 9.2 as follows

member-specification:

    member-declaration member-specification_opt


and can conclude that

struct str_pair_t drive;

is a member-declaration.


It is obvious to me that this is not a function-definition,
using-declaration, or template-declaration. The following possible
matches remain:

member-declaration:

    decl-specifier-seq_opt member-declarator-list_opt ;
    ::_opt nested-name-specifier template_opt unqualified-id ;



A nested-name-specifier must have "::" in it (Clause 5), so we conclude that

struct str_pair_t drive;

must match

decl-specifier-seq_opt member-declarator-list_opt ;


There is no comma in the statement, so the optional
member-declarator-list might be (9.2)

member-declarator-list:

    member-declarator



Here, the only possible matches are

member-declarator:

    declarator pure-specifier_opt
    declarator constant-initializer_opt


which are both the same in this case: declarator.


 From Clause 8, the only possible match is

declarator:

    direct-declarator


and

direct-declarator:

    declarator-id


and

declarator-id:

    id-expression
    ::_opt nested-name-specifier_opt type-name



 From Clause 5.1,

id-expression:

    unqualified-id
    qualified-id


and we have a match on

unqualified-id:

    identifier



Therefore,

struct str_pair_t drive;

matches

decl-specifier-seq_ identifier ;

where drive is the identifier.


 From Clause 7.1,

decl-specifier-seq:

    decl-specifier-seq_opt decl-specifier


and

decl-specifier:

    storage-class-specifier
    *type-specifier*
    function-specifier
    friend
    typedef



I expect

struct str_pair

to be a type-specifier, but I don't see how it matches that.

--

Alan Feldstein

Cosmic Horizon logo

http://www.alanfeldstein.com/

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"Alan M. Feldstein" wrote:
> I'm having trouble understanding how the following code maps to the
> syntax specified in ISO/IEC 14882:2003.
>
> typedef union {
> .
>       struct str_pair_t drive;
> .
> } yystype;
>
> (The ellipses respresent suppression of detail superfluous to this
> discussion.)
>
>
> This is in the form
>
> typedef type-specifier yystype;
>
> and I'm having no problem with that part.
>....
> I expect
>
> struct str_pair
>
> to be a type-specifier, but I don't see how it matches that.

The presence of the "struct" keyword (usually present for C
compatibility) means that the type-specifier has to be reduced to an
elaborated-type-specifier. An elaborated-type-specifier has the
following syntax:

      class-key ::_opt nested-name-specifier_opt identifier

Since the middle two terms are optional, "struct str_pair" matches:

      class-key identifier

Greg

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Alan M. Feldstein ha scritto:
>
> I expect
>
> struct str_pair
>
> to be a type-specifier, but I don't see how it matches that.
>

  7.1.5.3/1

elaborated-type-specifier:
   class-key ::opt nested-name-specifier opt identifier
   class-key ::opt nested-name-specifier opt template opt template-id
   enum ::opt nested-name-specifier opt identifier
   typename ::opt nested-name-specifier identifier
   typename ::opt nested-name-specifier template opt template-id


So "struct str_pair" is an elaborated-type-specifier, matching the first
production rule with class-key == "struct" (see   9/1) and identifier ==
"str_pair" (see 2.10/1).

  7.1.5/1

type-specifier:
   simple-type-specifier
   class-specifier
   enum-specifier
   elaborated-type-specifier
   cv-qualifier

So "struct str_pair" is a type-specifier, matching the fourth production
rule.

HTH,

Ganesh

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