The auto keyword is a declaration specifier. However, the C++ standard defines an original and a revised meaning for this keyword. Before Visual Studio 2010, the auto keyword declares a variable in the automatic storage class; that is, a variable that has a local lifetime. Starting with Visual Studio 2010, the auto keyword declares a variable whose type is deduced from the initialization expression in its declaration. The /Zc:auto[-] compiler option controls the meaning of the auto keyword.

auto declarator ;
auto declarator initializer;

The definition of the auto keyword changes in the C++ programming language, but not in the C programming language.

The following topics describe the auto keyword and the corresponding compiler option:

• auto describes the new definition of the auto keyword.

• /Zc:auto (Deduce Variable Type) describes the compiler option that tells the compiler which definition of the auto keyword to use.

Keywords