The auto storage class specifier lets you explicitly declare a variable with automatic storage. The auto storage class is the default for variables declared inside a block. A variable x that has automatic storage is deleted when the block in which x was declared exits.
You can only apply the auto storage class specifier to names of variables declared in a block or to names of function parameters. However, these names by default have automatic storage. Therefore the storage class specifier auto is usually redundant in a data declaration.
Storage duration of automatic variables
Objects with the auto storage class specifier have automatic storage duration. Each time a block is entered, storage for auto objects defined in that block is made available. When the block is exited, the objects are no longer available for use. An object declared with no linkage specification and without the static storage class specifier has automatic storage duration.
If an auto object is defined within a function that is recursively invoked, memory is allocated for the object at each invocation of the block.
Linkage of automatic variables
An auto variable has block scope and no linkage.
In C++0x,
the keyword auto is no longer used as a storage class
specifier. Instead, it is used as a type specifier. The compiler deduces
the type of an auto variable from the type of its
initializer expression. For more information, see The auto type specifier (C++0x).