| Internal Linkage |
Internal linkage occurs
where identical identifiers within a single source file
refer to the same data object or function. The following kinds of labels have internal
linkage:
- All identifiers with file or block
scope that have the keyword static
in their declarations. Functions with static
storage class are visible only in the source file
in which you define them.
- Functions qualified with _Inline and C++ inline
functions.
- All identifiers declared at file
scope with the specifier const
and not explicitly declared extern.
A variable that has static
storage class can be defined within a block or outside of
a function.
- If the definition occurs within
the block, the variable has internal linkage and
is visible only within the block after its
declaration is seen.
- If the definition occurs outside
of a function, the variable has internal linkage,
and is available from the point where it is
defined until the end of the current source file.
A class name that has no static members
or non-inline member functions, and that has not been
used in the declaration of an object, function, or class,
is local to its translation unit.
If the declaration of an identifier has
the keyword extern, and if a previous
declaration of the identifier is visible at file scope,
the identifier has the same linkage as the first
declaration.
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| No Linkage |
No linkage occurs where
each identical identifier refers to a unique object. The following kinds of identifiers have no
linkage:
- Identifiers that do not represent
an object or a function, including labels,
enumerators, typedef names, type
names, and template names.
- Identifiers that represent a
function argument.
- Identifiers declared inside a
block without the keyword extern.
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