Some questions about struct namespace in C





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I'm trying to understand this answer - typedef struct vs struct definitions [duplicate]:




(Line 3): ["] In the first line you are defining the identifier S within the struct name space (not in the C++ sense). [."]





  1. It seems like for struct X {...};, the {...} is like an adjective for X, and X {...} is thrown into something called struct-namespace, how many struct-namespace are there in a program? Is there only one specified by struct?

  2. It seems like in C/C++ struct and class are almost the same? So in C++ struct and class are both in class-namespace?






c struct







share|improve this question




















  • 1





    A c++ struct is simply a class that defaults to public.

    – Goswin von Brederlow
    Nov 23 '18 at 16:18











  • @GoswinvonBrederlow: Got it, thank you!

    – BinaryTreeee
    Nov 23 '18 at 16:34


















0















I'm trying to understand this answer - typedef struct vs struct definitions [duplicate]:




(Line 3): ["] In the first line you are defining the identifier S within the struct name space (not in the C++ sense). [."]





  1. It seems like for struct X {...};, the {...} is like an adjective for X, and X {...} is thrown into something called struct-namespace, how many struct-namespace are there in a program? Is there only one specified by struct?

  2. It seems like in C/C++ struct and class are almost the same? So in C++ struct and class are both in class-namespace?






c struct







share|improve this question




















  • 1





    A c++ struct is simply a class that defaults to public.

    – Goswin von Brederlow
    Nov 23 '18 at 16:18











  • @GoswinvonBrederlow: Got it, thank you!

    – BinaryTreeee
    Nov 23 '18 at 16:34














0












0








0








I'm trying to understand this answer - typedef struct vs struct definitions [duplicate]:




(Line 3): ["] In the first line you are defining the identifier S within the struct name space (not in the C++ sense). [."]





  1. It seems like for struct X {...};, the {...} is like an adjective for X, and X {...} is thrown into something called struct-namespace, how many struct-namespace are there in a program? Is there only one specified by struct?

  2. It seems like in C/C++ struct and class are almost the same? So in C++ struct and class are both in class-namespace?






c struct







share|improve this question
















I'm trying to understand this answer - typedef struct vs struct definitions [duplicate]:




(Line 3): ["] In the first line you are defining the identifier S within the struct name space (not in the C++ sense). [."]





  1. It seems like for struct X {...};, the {...} is like an adjective for X, and X {...} is thrown into something called struct-namespace, how many struct-namespace are there in a program? Is there only one specified by struct?

  2. It seems like in C/C++ struct and class are almost the same? So in C++ struct and class are both in class-namespace?






c struct




c struct






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 23 '18 at 14:17







BinaryTreeee

















asked Nov 23 '18 at 14:16









BinaryTreeeeBinaryTreeee

606424




606424








  • 1





    A c++ struct is simply a class that defaults to public.

    – Goswin von Brederlow
    Nov 23 '18 at 16:18











  • @GoswinvonBrederlow: Got it, thank you!

    – BinaryTreeee
    Nov 23 '18 at 16:34














  • 1





    A c++ struct is simply a class that defaults to public.

    – Goswin von Brederlow
    Nov 23 '18 at 16:18











  • @GoswinvonBrederlow: Got it, thank you!

    – BinaryTreeee
    Nov 23 '18 at 16:34








1




1





A c++ struct is simply a class that defaults to public.

– Goswin von Brederlow
Nov 23 '18 at 16:18





A c++ struct is simply a class that defaults to public.

– Goswin von Brederlow
Nov 23 '18 at 16:18













@GoswinvonBrederlow: Got it, thank you!

– BinaryTreeee
Nov 23 '18 at 16:34





@GoswinvonBrederlow: Got it, thank you!

– BinaryTreeee
Nov 23 '18 at 16:34












2 Answers
2






active

oldest

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0














1 (for C): there is one namespace for all structure tags. You can have as many different tags as you want, even if the same name is used in other namespaces.



Each structure on its own is its own namespace (there are "infinite" struct namespaces).



// You can have

struct foo { int var; }

struct bar { double var; }

struct baz { int var; }

struct qux { int var; }

// with no conflict between all the `var`





share|improve this answer


























  • So each different X is a namespace?

    – BinaryTreeee
    Nov 23 '18 at 14:20






  • 1





    sort of, if you have a struct one, one is an identifier belonging to the struct namespace. one can also be one or more identifier(s) in other namespaces.

    – pmg
    Nov 23 '18 at 14:27













  • OK, so struct {...} one, two, three; only one namespaces and three identifiers for it? And is that in this case the struct is anonymous?

    – BinaryTreeee
    Nov 23 '18 at 14:30











  • still not quite right. in struct {...} one, two, three; there is no identifier for the struct namespace: it's a struct without a tag (an anonymous struct, using no namespace). The identifiers one, two, and three belong to the regular namespace.

    – pmg
    Nov 23 '18 at 14:33








  • 1





    Yes, the same meaning :)

    – pmg
    Nov 23 '18 at 14:41



















1














From the C99 standard draft



6.2.3




6.2.3 Name spaces of identifiers



If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate namespaces
for various categories of identifiers, as follows:



—label names
(disambiguated by the syntax of the label declaration and use);



—the
tags
of structures, unions, and enumerations (disambiguated by following any
of the keywords
struct
,
union
,or
enum
);



—the
members
of structures or unions; each structure or union has a separate name
space for its members (disambiguated by the type of the expression used to access the
member via the
.
or
->
operator);



—all other identifiers, called
ordinary identifiers
(declared in ordinary declarators or as
enumeration constants).




In other words, if you have struct S, then S is in the struct namespace, whereas if you have int S as well, then it's in the namespace of ordinary identifiers.



This is not the case for C++






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    2 Answers
    2






    active

    oldest

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    2 Answers
    2






    active

    oldest

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    active

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    votes






    active

    oldest

    votes









    0














    1 (for C): there is one namespace for all structure tags. You can have as many different tags as you want, even if the same name is used in other namespaces.



    Each structure on its own is its own namespace (there are "infinite" struct namespaces).



    // You can have
    
struct foo { int var; }
    
struct bar { double var; }
    
struct baz { int var; }
    
struct qux { int var; }
    
// with no conflict between all the `var`





    share|improve this answer


























    • So each different X is a namespace?

      – BinaryTreeee
      Nov 23 '18 at 14:20






    • 1





      sort of, if you have a struct one, one is an identifier belonging to the struct namespace. one can also be one or more identifier(s) in other namespaces.

      – pmg
      Nov 23 '18 at 14:27













    • OK, so struct {...} one, two, three; only one namespaces and three identifiers for it? And is that in this case the struct is anonymous?

      – BinaryTreeee
      Nov 23 '18 at 14:30











    • still not quite right. in struct {...} one, two, three; there is no identifier for the struct namespace: it's a struct without a tag (an anonymous struct, using no namespace). The identifiers one, two, and three belong to the regular namespace.

      – pmg
      Nov 23 '18 at 14:33








    • 1





      Yes, the same meaning :)

      – pmg
      Nov 23 '18 at 14:41
















    0














    1 (for C): there is one namespace for all structure tags. You can have as many different tags as you want, even if the same name is used in other namespaces.



    Each structure on its own is its own namespace (there are "infinite" struct namespaces).



    // You can have
    
struct foo { int var; }
    
struct bar { double var; }
    
struct baz { int var; }
    
struct qux { int var; }
    
// with no conflict between all the `var`





    share|improve this answer


























    • So each different X is a namespace?

      – BinaryTreeee
      Nov 23 '18 at 14:20






    • 1





      sort of, if you have a struct one, one is an identifier belonging to the struct namespace. one can also be one or more identifier(s) in other namespaces.

      – pmg
      Nov 23 '18 at 14:27













    • OK, so struct {...} one, two, three; only one namespaces and three identifiers for it? And is that in this case the struct is anonymous?

      – BinaryTreeee
      Nov 23 '18 at 14:30











    • still not quite right. in struct {...} one, two, three; there is no identifier for the struct namespace: it's a struct without a tag (an anonymous struct, using no namespace). The identifiers one, two, and three belong to the regular namespace.

      – pmg
      Nov 23 '18 at 14:33








    • 1





      Yes, the same meaning :)

      – pmg
      Nov 23 '18 at 14:41














    0












    0








    0







    1 (for C): there is one namespace for all structure tags. You can have as many different tags as you want, even if the same name is used in other namespaces.



    Each structure on its own is its own namespace (there are "infinite" struct namespaces).



    // You can have
    
struct foo { int var; }
    
struct bar { double var; }
    
struct baz { int var; }
    
struct qux { int var; }
    
// with no conflict between all the `var`





    share|improve this answer















    1 (for C): there is one namespace for all structure tags. You can have as many different tags as you want, even if the same name is used in other namespaces.



    Each structure on its own is its own namespace (there are "infinite" struct namespaces).



    // You can have
    
struct foo { int var; }
    
struct bar { double var; }
    
struct baz { int var; }
    
struct qux { int var; }
    
// with no conflict between all the `var`






    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited Nov 23 '18 at 14:40

























    answered Nov 23 '18 at 14:17









    pmgpmg

    84.8k9100171




    84.8k9100171













    • So each different X is a namespace?

      – BinaryTreeee
      Nov 23 '18 at 14:20






    • 1





      sort of, if you have a struct one, one is an identifier belonging to the struct namespace. one can also be one or more identifier(s) in other namespaces.

      – pmg
      Nov 23 '18 at 14:27













    • OK, so struct {...} one, two, three; only one namespaces and three identifiers for it? And is that in this case the struct is anonymous?

      – BinaryTreeee
      Nov 23 '18 at 14:30











    • still not quite right. in struct {...} one, two, three; there is no identifier for the struct namespace: it's a struct without a tag (an anonymous struct, using no namespace). The identifiers one, two, and three belong to the regular namespace.

      – pmg
      Nov 23 '18 at 14:33








    • 1





      Yes, the same meaning :)

      – pmg
      Nov 23 '18 at 14:41



















    • So each different X is a namespace?

      – BinaryTreeee
      Nov 23 '18 at 14:20






    • 1





      sort of, if you have a struct one, one is an identifier belonging to the struct namespace. one can also be one or more identifier(s) in other namespaces.

      – pmg
      Nov 23 '18 at 14:27













    • OK, so struct {...} one, two, three; only one namespaces and three identifiers for it? And is that in this case the struct is anonymous?

      – BinaryTreeee
      Nov 23 '18 at 14:30











    • still not quite right. in struct {...} one, two, three; there is no identifier for the struct namespace: it's a struct without a tag (an anonymous struct, using no namespace). The identifiers one, two, and three belong to the regular namespace.

      – pmg
      Nov 23 '18 at 14:33








    • 1





      Yes, the same meaning :)

      – pmg
      Nov 23 '18 at 14:41

















    So each different X is a namespace?

    – BinaryTreeee
    Nov 23 '18 at 14:20





    So each different X is a namespace?

    – BinaryTreeee
    Nov 23 '18 at 14:20




    1




    1





    sort of, if you have a struct one, one is an identifier belonging to the struct namespace. one can also be one or more identifier(s) in other namespaces.

    – pmg
    Nov 23 '18 at 14:27







    sort of, if you have a struct one, one is an identifier belonging to the struct namespace. one can also be one or more identifier(s) in other namespaces.

    – pmg
    Nov 23 '18 at 14:27















    OK, so struct {...} one, two, three; only one namespaces and three identifiers for it? And is that in this case the struct is anonymous?

    – BinaryTreeee
    Nov 23 '18 at 14:30





    OK, so struct {...} one, two, three; only one namespaces and three identifiers for it? And is that in this case the struct is anonymous?

    – BinaryTreeee
    Nov 23 '18 at 14:30













    still not quite right. in struct {...} one, two, three; there is no identifier for the struct namespace: it's a struct without a tag (an anonymous struct, using no namespace). The identifiers one, two, and three belong to the regular namespace.

    – pmg
    Nov 23 '18 at 14:33







    still not quite right. in struct {...} one, two, three; there is no identifier for the struct namespace: it's a struct without a tag (an anonymous struct, using no namespace). The identifiers one, two, and three belong to the regular namespace.

    – pmg
    Nov 23 '18 at 14:33






    1




    1





    Yes, the same meaning :)

    – pmg
    Nov 23 '18 at 14:41





    Yes, the same meaning :)

    – pmg
    Nov 23 '18 at 14:41













    1














    From the C99 standard draft



    6.2.3




    6.2.3 Name spaces of identifiers



    If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate namespaces
    for various categories of identifiers, as follows:



    —label names
    (disambiguated by the syntax of the label declaration and use);



    —the
    tags
    of structures, unions, and enumerations (disambiguated by following any
    of the keywords
    struct
    ,
    union
    ,or
    enum
    );



    —the
    members
    of structures or unions; each structure or union has a separate name
    space for its members (disambiguated by the type of the expression used to access the
    member via the
    .
    or
    ->
    operator);



    —all other identifiers, called
    ordinary identifiers
    (declared in ordinary declarators or as
    enumeration constants).




    In other words, if you have struct S, then S is in the struct namespace, whereas if you have int S as well, then it's in the namespace of ordinary identifiers.



    This is not the case for C++






    share|improve this answer




























      1














      From the C99 standard draft



      6.2.3




      6.2.3 Name spaces of identifiers



      If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate namespaces
      for various categories of identifiers, as follows:



      —label names
      (disambiguated by the syntax of the label declaration and use);



      —the
      tags
      of structures, unions, and enumerations (disambiguated by following any
      of the keywords
      struct
      ,
      union
      ,or
      enum
      );



      —the
      members
      of structures or unions; each structure or union has a separate name
      space for its members (disambiguated by the type of the expression used to access the
      member via the
      .
      or
      ->
      operator);



      —all other identifiers, called
      ordinary identifiers
      (declared in ordinary declarators or as
      enumeration constants).




      In other words, if you have struct S, then S is in the struct namespace, whereas if you have int S as well, then it's in the namespace of ordinary identifiers.



      This is not the case for C++






      share|improve this answer


























        1












        1








        1







        From the C99 standard draft



        6.2.3




        6.2.3 Name spaces of identifiers



        If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate namespaces
        for various categories of identifiers, as follows:



        —label names
        (disambiguated by the syntax of the label declaration and use);



        —the
        tags
        of structures, unions, and enumerations (disambiguated by following any
        of the keywords
        struct
        ,
        union
        ,or
        enum
        );



        —the
        members
        of structures or unions; each structure or union has a separate name
        space for its members (disambiguated by the type of the expression used to access the
        member via the
        .
        or
        ->
        operator);



        —all other identifiers, called
        ordinary identifiers
        (declared in ordinary declarators or as
        enumeration constants).




        In other words, if you have struct S, then S is in the struct namespace, whereas if you have int S as well, then it's in the namespace of ordinary identifiers.



        This is not the case for C++






        share|improve this answer













        From the C99 standard draft



        6.2.3




        6.2.3 Name spaces of identifiers



        If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate namespaces
        for various categories of identifiers, as follows:



        —label names
        (disambiguated by the syntax of the label declaration and use);



        —the
        tags
        of structures, unions, and enumerations (disambiguated by following any
        of the keywords
        struct
        ,
        union
        ,or
        enum
        );



        —the
        members
        of structures or unions; each structure or union has a separate name
        space for its members (disambiguated by the type of the expression used to access the
        member via the
        .
        or
        ->
        operator);



        —all other identifiers, called
        ordinary identifiers
        (declared in ordinary declarators or as
        enumeration constants).




        In other words, if you have struct S, then S is in the struct namespace, whereas if you have int S as well, then it's in the namespace of ordinary identifiers.



        This is not the case for C++







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 23 '18 at 14:29









        JETMJETM

        2,15441731




        2,15441731






























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