These extensions are available in C and Objective C. Most of the extensions are also available in C++. See Extensions to the C++ language for extensions that apply only to C++.

See the following documentation for more specific discussion regarding extensions to the C language family.

• Statements and declarations in expressions
• Locally declared labels
• Labels as values
• Nested functions
• Constructing function calls
• Naming an expression’s type
• Referring to a type with typeof
• Generalized Lvalues
• Conditionals with omitted operands
• Double-word integers
• Complex numbers
• Arrays of length zero
• Arrays of variable length
• Macros with variable number of arguments
• Non-Lvalue arrays may have subscripts
• Arithmetic on void- and function-pointers
• Non-constant initializers
• Constructor expressions
• Labeled elements in initializers
• Case ranges
• Cast to a union yype
• Declaring attributes of functions
• Prototypes and old-style function definitions
• Compiling functions for interrupt calls
• C++ style comments
• Dollar signs in identifier names
• The ESC character in constants
• Inquiring on alignment of types or variables
• Specifying attributes of variables
• Specifying attributes of types
• An inline function is as fast as a macro
• Assembler instructions with C expression operands
• Constraints for asm operands
• Simple constraints
• Multiple alternative constraints
• Constraint modifier characters
• Constraints for particular machines
• Controlling names used in assembler code
• Variables in specified registers
• Defining global register variables
• Specifying registers for local variables
• Alternate keywords
• Incomplete enum types
• Function namers as strings
• Getting the return or frame address of a function