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Language Extensions
• In operations on pointers, a pointer to void is always implicitly converted to
another type if necessary. Also, a null pointer constant is always implicitly
converted to a null pointer of the right type if necessary. In ISO C, some operators
permit these, and others do not.
• Pointers to different function types can be assigned or compared for equality (==)
or inequality (!=) without an explicit type cast. A warning or error is issued.
This extension is prohibited in C++ mode.
• A pointer to void can be implicitly converted to, or from, a pointer to a function
type.
• In an initializer, a pointer constant value can be cast to an integral type if the
integral type is big enough to contain it.
• A non lvalue array expression is converted to a pointer to the first element of the
array when it is subscripted or similarly used.
3.4.3 Block scope function declarations
Two extensions to block scope function declarations are supported:
• a block-scope function declaration also declares the function name at file scope
• a block-scope function declaration can have static storage class, thereby causing
the resulting declaration to have internal linkage by default.
Example
void f1(void)
{
static void g(void); /* static function declared in local scope */
/* use of static keyword is illegal in strict ISO C */
}
void f2(void)
{
g(); /* uses previous local declaration */
}
static void g(int i)
{ } /* error - conflicts with previous declaration of g */
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