The storage-class modifiers allow individual attributes of a
variable to change without changing the other default attributes
connected with a given storage class. Storage-class keywords and
storage-class modifiers can be specified in either order.
Syntax:
modifier storage_class_keyword identifier;
If you specify a storage-class modifier but not a storage class
keyword, the storage class defaults to extern.
1 – noshare
Noshare variables are assigned the PSECT attribute NOSHR. Noshare
variables may not be shared between processes. This modifier is
used when linking variables that are not to be shared within a
shareable image. You can use the noshare modifier with the
storage-class keywords static, [extern], globaldef, and
globaldef{"name"}.
2 – readonly
Readonly variables are assigned the PSECT attribute NOWRT and are
stored in the PSECT $READONLY$ which is a nonwritable data area.
Other programs can access the PSECT directly, but none of the
information can be overwritten. You can use the readonly modifier
with the storage-class keywords [extern], static, globaldef, and
globaldef{"name"}.
You can use both the readonly and noshare modifiers with the
[extern] and the globaldef{"name"} specifiers. If you use both
modifiers with either the static or the globaldef specifiers, the
compiler ignores noshare and accepts readonly.
3 – _align
The _align modifier allows you to align objects of any of the VSI C
data types on a specified storage boundary. Use the _align
modifier in a data declaration or definition.
When specifying the boundary of the data alignment, you can use a
predefined constant: BYTE or byte, WORD or word, LONGWORD or
longword, QUADWORD or quadword, OCTAWORD or octaword, and PAGE or
page.
You can also specify an integer value that is a power of two. The
power of two tells VSI C the number of bytes to pad in order to
align the data:
For OpenVMS VAX systems, specify a constant 0, 1, 2, 3, 4, or 9.
For OpenVMS Alpha systems, specify any constant from 0 to 16.
4 – __align
The __align storage-class modifier has the same semantic meaning as the _align keyword. The difference is that __align is a keyword in all compiler modes while _align is a keyword only in modes that recognize VAX C keywords. For new programs, using __align is recommended.
5 – __forceinline
Similar to the __inline storage-class modifier, the __forceinline
storage-class modifier marks a function for inline expansion.
However, using __forceinline on a function definition and prototype
tells the compiler that it must substitute the code within the
function definition for every call to that function. (With
__inline, such substitution occurs at the discretion of the
compiler.)
Syntax:
__forceinline [type] function_definition
6 – __inline
The __inline modifier marks a function for inline expansion. Using
__inline on a function definition and prototype tells the compiler
that it can substitute the code within the function definition for
every call to that function. Substitution occurs at the discretion
of the compiler. The __inline storage-class specifier has the same
effect as the #pragma inline preprocessor directive, except that
the latter attempts to provide inline expansion for all functions
in a translation unit, rather than for selected functions.
Syntax:
__inline [type] function_definition
7 – inline
Similar to the __inline storage-class modifier, the inline
storage-class modifier can be used as a declaration specifier in
the declaration of a function. This modifier is supported in
relaxed ANSI C mode (/STANDARD=RELAXED) or if the
/ACCEPT=C99_KEYWORDS or /ACCEPT=GCCINLINE qualifier is specified.
With static functions, inline has the same effect as applying
__inline or #pragma inline to the function.
However, when inline is applied to a function with external
linkage, besides allowing calls within that translation unit to be
inlined, the inline semantics provide additional rules that also
allow calls to the function to be inlined in other translation
units or for the function to be called as an external function, at
the compiler's discretion:
o If the inline keyword is used on a function declaration with
external linkage, then the function must also be defined in the
same translation unit.
o If all of the file scope declarations of the function use the
inline keyword but do not use the extern keyword, then the
definition in that translation unit is called an inline
definition, and no externally-callable definition is produced
by that compilation unit.
Otherwise, the compilation unit does produce an
externally-callable definition.
o An inline definition must not contain a definition of a
modifiable object with static storage duration, and it must not
refer to an identifier with internal linkage. These
restrictions do not apply to the externally-callable
definition.
o As usual, at most one compilation unit in an entire program can
supply an externally-callable definition of a given function.
o Any call to a function with external linkage may be translated
as a call to an external function, regardless of the presence
of the inline qualifier. It follows from this and the previous
point that any function with external linkage that is called
must have exactly one externally-callable definition among all
the compilation units of an entire program.
o The address of an inline function with external linkage is
always computed as the address of the unique
externally-callable definition, never the address of an inline
definition.
o A call to inline function made through a pointer to the
externally-callable definition may still be inlined or
translated as a call to an inline definition, if the compiler
can determine the name of the function whose address was stored
in the pointer.