Keywords

Keywords are identifiers reserved by the language for special use. Although you can use them for preprocessor macro names, it is considered poor programming style. Only the exact spelling of keywords is reserved. For example, auto is reserved but AUTO is not.

Keywords for the C and C++ languages

Table 1. C and C++ keywords
auto¹ break case char const continue default do	double else enum extern² float for goto if	int long register return short signed sizeof static	struct switch typedef union unsigned void volatile while
Notes: In C++11, the keyword `auto` is no longer used as a storage class specifier. Instead, it is used as a type specifier, which can deduce the type of an `auto` variable from the type of its initializer expression. The keyword `extern` was previously used as a storage specifier or as part of a linkage specification. The C++11 standard adds a third usage to use this keyword to specify explicit instantiation declarations.

Keywords for the C language only

Standard C at the C99 and C11 levels also reserves the following keywords:

Table 2. C99 and C11 keywords
_Atomic¹ _Bool _Complex _Generic¹ _Imaginary²	inline³ _Noreturn¹ _Static_assert¹ restrict⁴
Notes: These keywords are introduced due to the C11 language level. The keyword `_Imaginary` is reserved for possible future use. For complex number functionality, use `_Complex`; see Complex literals (C only) for details. The keyword `inline` is only recognized under compilation with c99 and above, or with the LANGLVL(STDC99) or LANGLVL(EXTC99) options. The keyword `restrict` is only recognized under compilation with c99 and above, or with the LANGLVL(STDC99) or LANGLVL(EXTC99) options.

Keywords for the C++ language only

The C++ language also reserves the following keywords:

Table 3. C++ keywords
bool catch class char16_t¹ char32_t¹ const_cast constexpr delete	dynamic_cast decltype explicit export false friend inline mutable namespace	new operator private protected public reinterpret_cast static_assert static_cast template	this throw true try typeid typename using virtual wchar_t
Note: These keywords are reserved only at the C++11 language level.

Keywords for language extensions (IBM extension)

In addition to standard language keywords, the z/OS® XL C/C++ compiler reserves the following keywords for use in language extensions:

Table 4. Keywords for C and C++ language extensions
asm __asm __asm__ __attribute__ __attribute __complex__ (C only) __const__ __extension__	__imag__ (C only) __inline__ _Noreturn² __real__ (C only) __restrict __restrict__ __signed__	__signed __static_assert¹ typeof (C only) __typeof__ vector³ __vector³ __volatile (C++ only) __volatile__ (C++ only)
Notes: `__static_assert` is a keyword for C language extension for compatibility with the C++11 standard. `_Noreturn` is a keyword for C++ language extension for compatibility with the C11 standard. These keywords are recognized only when the VECTOR compiler option is in effect.

The z/OS XL C/C++ compiler reserves the following keywords as language extensions for compatibility with C99.

Table 5. Keywords for C++ language extensions related to C99
restrict

z/OS XL C/C++ additionally reserves the following for use as extensions:

Table 6. Keywords for C/C++ language extensions on z/OS
_Packed __packed	__cdecl _Export	__callback __ptr32 __ptr64 __far¹

Note:

Recognized only when the METAL compiler option is in effect, which is currently only supported by z/OS XL C.

z/OS XL C/C++ also reserves the following keywords for future use in both C and C++:

Table 7. Reserved keywords for future use
__alignof__ __extension__ __label__ _Pragma

More detailed information regarding the compilation contexts in which extension keywords are valid is provided in the sections that describe each keyword.