C99 features

The following features are enabled by default when you compile with any of the following commands:

For more information on these options, see the -qlanglvl option .

Table 1. Default C99 features as extensions to C89
Language feature	Discussed in:
Hexadecimal floating-point constants	Hexadecimal floating-point literals
`__func__` predefined identifier	The __func__ predefined identifier
Concatenation of wide and non-wide character strings	String concatenation
Mixed declarations and code	Overview of data declarations and definitions
Complex data type	Complex floating-point types
`_Bool` data type	Boolean types
Trailing comma allowed in `enum` declaration	Enumeration type definition
Duplicate type qualifiers	Type qualifiers
Variable length arrays	Variable length arrays
Non-lvalue array subscripts	Array subscripting operator [ ]
Flexible array members at the end of a structure or union	Flexible array members
Non-constant expression in initializer for structure or union	Initialization of structures and unions
Designated initializers	Designated initializers for aggregate types
Removal of implicit function declaration	Function declarations
Removal of implicit `int` return type in function declarations	Function return type specifiers
Static arrays as function parameters	Static array indices in function parameter declarations (C only)
Variable arguments in function-like macros	Function-like macros
Empty arguments in function-like macros	Function-like macros
Additional predefined macro names	Standard predefined macro names
Compound literals	Compound literal expressions
`_Pragma` operator	The _Pragma preprocessing operator
Standard pragmas	Standard pragmas

The following features are enabled by default when you compile with any of the following commands:

They are also enabled or disabled by specific compiler options, which are listed in the below table:

Table 2. Default C99 features as extensions to C89, with individual option controls
Language feature	Discussed in:	Individual option control
Digraphs	Digraph characters	-q[no]digraph
C++ style comments	Comments	-q[no]cpluscmt
The `inline` function specifier	The inline function specifier	-qkeyword=inline

The following feature is enabled by default when you compile with any of the following commands:

Table 3. Strict C99 features as extensions to C89
Language feature	Discussed in:
C99 `long long`	Types of integer literals in C99
Note: This feature is incompatible with the semantics of the `long long` types controlled by the -qlonglong option. For details, see -qlonglong.

The following features are enabled by default when you compile with any of the following commands:

They are also enabled or disabled by specific compiler options, which are listed in the below table:

Table 4. Strict C99 features as extensions to C89, with individual option controls
Language feature	Discussed in:	Individual option control
Universal character names	The Unicode standard	-qlanglvl=[no]ucs
The `restrict` type qualifier	The restrict type qualifier	-qkeyword=restrict