C++Talk.NET

Alan M. Feldstein · Guest

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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Greg Herlihy · Guest

"Alan M. Feldstein" wrote:

Alberto Ganesh Barbati · Guest

Alan M. Feldstein ha scritto: