STRUC            Define structure type                              Directive

  STRUC name                            ; Ideal mode
     structure_members
  ENDS [name]

  name STRUC                            ; MASM mode
     structure_members
  [name] ENDS

    Defines a structure called name containing members.


    Structures and unions

    Structures and unions let you mix and match various types. A structure
    in Turbo Assembler is a data type that contains one or more data
    elements called members. The size of a structure is the combined
    size of all data elements within it.

    Unions are similar to structures, except that all of the members in a
    union occupy the same memory. The size of a union is the size of its
    largest member. Unions are useful when a block of memory must
    represent one of several distinct possibilities, each with different
    data storage requirements.

    Turbo Assembler lets you fully nest structures and unions within one
    another, but this can become complicated. For example, you could have
    a structure member that is really a union. A union could also have a
    full structure as each member.


    Opening and closing a structure or union

    TASM considers all data or code emitted between the time a structure
    or union data type definition is opened (STRUC or UNION directive) and
    the time a corresponding ENDS directive is encountered to be part of
    that structure or union data type.

    Turbo Assembler treats structure and union data type names as global
    but redefinable. You can define the same name as a structure or union
    data type more than once in a module.


    Specifying members

    To create members in a structure or union definition, use the same
    directives as those for allocating data and creating labels in an open
    segment. Turbo Assembler allows all methods of allocating data with a
    structure definition, including instances of other structures, unions,
    records, enumerated data types, tables, and objects.

    Members may be named or remain nameless. MASM and Ideal mode treat
    structure member names differently. In MASM mode, structure member
    names are global and cannot be redefined. In Ideal mode, structure
    member names are considered local to a structure or union data type.


    The LABEL directive lets you create structure members without
    allocating data. LABEL directives found inside structure definitions
    define members of the structure.

    You can use the ALIGN directive within structure definitions to align
    structure members on appropriate boundaries.


    Example:    STRUC testx
                   mem1     db   ?
                   mem2     dw   5
                LABEL xrest WORD
                ALIGN 4
                   mem3     dd   ?
                ENDS


    Nesting structures and unions

    TASM lets you nest the STRUC, UNION, and ENDS directives inside open
    structure and union data type definitions to control the offsets
    assigned to structure members.

    In a structure, each data element begins where the previous one ended.
    In a union, each data element begins at the same offset as the
    previous one. Allowing a single data element to consist of an entire
    union or structure provides a high degree of flexibility.


    Incorporating one named structure within another

    TASM provides a way of incorporating an entire existing structure or
    union data type, including member names, into an open structure
    definition to assist in the inheritance of objects. It treats the
    incorporated structure or union as if it were nested inside the open
    structure or union definition at that point. In this way,
    incorporating a structure or union into another is intrinsically
    different from including an instance of a structure or union in
    another; an instance includes only initialized or uninitialized
    data, while incorporation includes data, structure, and member
    names.

    Refer to the TASM documentation for details.


    Creating an instance of a structure or union

    To create an instance of a structure or union data type, use the
    structure or union data name as a data allocation directive.

    Examples:   stest1 mystruc ?                  ; uninitialized
                stest2 mystruc < >                ; initialized to defaults
                stest3 mystruc { }                ; initialized to defaults
                stest4 mystruc {mem2=2, mem4=?}   ; initialize named members
                stest5 mystruc <,2,,?>            ; initialize members

  ──────────────────────────────────────────────────────────────────────────
  Extended STRUC directive:

  STRUC name [modifiers] [parent_name] [METHOD [method_list]]   ; Ideal mode
     structure_members
  ENDS [name]

    Turbo Assembler 3.1+ objects are also defined as structures having
    the extra optional items on the struc line.

    name                is the name of the object
    modifiers           can be one or more of: GLOBAL, NEAR, FAR
    parent_name         is the name of the parent object's data structure
                        (single inheritance supported)
    method_list         is like that of TABLE
    structure_members   are any (additional) data present in an instance
                        of the object

    The extended STRUC directive defines or uses several symbols which
    reflect the object being defined:

    @Object                  Text macro containing the name of the current
                             object
    @Table_<objectname>      Data type containing the object's method table
    @Tableaddr_<objectname>  A label describing the address of the
                             instance of the object's virtual method table
                             (VMT).