Variable length arrays
A variable length array, which is a C99 feature, is an array of automatic storage duration whose length is determined at runtime.
If the size of the array is indicated by * instead
of an expression, the variable length array is considered to be of
unspecified size. Such arrays are considered complete types, but can
only be used in declarations of function prototype scope.
A variable length
array and a pointer to a variable length array are considered variably
modified types. Declarations of variably modified types must be
at either block scope or function prototype scope. Array objects declared
with the extern storage class specifier cannot be
of variable length array type. Array objects declared with the static storage
class specifier can be a pointer to a variable length array, but not
an actual variable length array. A variable length array cannot be
initialized.
A
variable length array can be the operand of a sizeof expression.
In this case, the operand is evaluated at runtime, and the size is
neither an integer constant nor a constant expression, even though
the size of each instance of a variable array does not change during
its lifetime.
A
variable length array can be used in a typedef statement.
The typedef name will have only block scope. The
length of the array is fixed when the typedef name
is defined, not each time it is used.
void f(int x, int a[][x]);The C++ extension does not include support for references to a variable length array type; neither may a function parameter be a reference to a variable length array type.