HP 3000 Manuals HP 3000 Manuals
Storage-Class Specifiers
A storage-class specifier is one of several keywords that determines the
duration and linkage of an object.
Syntax
storage-class ::=
typedef
extern
static
auto
register
Description
You can use only one storage-class specifier in a declaration.
The typedef keyword is listed as a storage-class specifier because it is
syntactically similar to one.
The keyword extern affects the linkage of a function or object name. If
the name has already been declared in a declaration with file scope, the
linkage will be the same as in that previous declaration. Otherwise, the
name will have external linkage.
The static storage-class specifier may appear in declarations of
functions or data objects. If used in an external declaration (either a
function or a data object), static indicates that the name cannot be
referenced by other translation units. Using the static storage class in
this way allows translation units to have collections of local functions
and data objects that are not exported to other translation units at link
time.
If the static storage class is used in a declaration within a function,
the value of the variable is preserved between invocations of that
function.
The auto storage-class specifier is permitted only in the declarations of
objects within blocks. An automatic variable is one that exists only
while its enclosing block is being executed. Variables declared with the
auto storage-class are all allocated when a function is entered. Auto
variables that have initializers are initialized when their defining
block is entered normally. This means that auto variables with
initializers are not initialized when their declaring block is not
entered through the top.
The register storage class suggests that the compiler store the variable
in a register, if possible. You cannot apply the & (address-of) operator
to register variables.
If no storage class is specified and the declaration appears in a block,
the compiler defaults the storage duration for an object to automatic.
If the declaration of an identifier for a function has no storage-class
specifier, its linkage is determined exactly as if it were declared with
the extern storage-class specifier.
If no storage class is specified and the declaration appears outside of a
function, the compiler treats it as an externally visible object with
static duration.
Refer to chapter 2 for a description of storage duration and linkage.