Reserved keywords in C are a set valid identifier names which are part of the grammar of C and therefore may not be used for anything but their intended purpose. That is, they may not be used as variable names, function names, or an any other type of identifiers. Just like all other identifier in C, they are case sensitive.

The table below lists all keywords reserved by the C language.

auto break case char const continue default do double else

enum extern float for goto if inline1 int long register

restrict1 return short signed sizeof static struct switch typedef union

unsigned void volatile while _Alignas2 _Alignof2 _Atomic2 _Bool1 _Complex1

_Generic2 _Imaginary1 _Noreturn2 _Static_assert2 _Thread_local2

¹ - Keywords added in C99.
² - Keywords added in C11.

C99 changes from C89

C99 added the following keywords:

• inline
• restrict
• _Bool
• _Complex
• _Imaginary

C11 changes from C99

C11 added the following keywords:

• _Alignas
• _Alignof
• _Atomic
• _Generic
• _Noreturn
• _Static_assert
• _Thread_local