The iso646.h header file is part of the C standard library

C standard library

The C Standard Library is the standard library for the programming language C, as specified in the ANSI C standard.. It was developed at the same time as the C POSIX library, which is basically a superset of it...

. It was added to this library in a 1995 amendment to the C90 standard. It defines a number of macros which allow programmers to use C language

C (programming language)

C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

 bitwise and logical operators

Operator (programming)

Programming languages typically support a set of operators: operations which differ from the language's functions in calling syntax and/or argument passing mode. Common examples that differ by syntax are mathematical arithmetic operations, e.g...

, which, without the header file, cannot be quickly or easily typed on some international

International

----International mostly means something that involves more than one country. The term international as a word means involvement of, interaction between or encompassing more than one nation, or generally beyond national boundaries...

 and non-QWERTY

QWERTY

QWERTY is the most common modern-day keyboard layout. The name comes from the first six letters appearing in the topleft letter row of the keyboard, read left to right: Q-W-E-R-T-Y. The QWERTY design is based on a layout created for the Sholes and Glidden typewriter and sold to Remington in the...

 keyboards.

The filename refers to the ISO646 standard, a 7-bit character set with a number of regional variations, some of which have accented characters in place of the punctuation marks used by C operators.

The macros

The iso646.h header defines the following 11 macros as stated below:

Macro	Defined as
and	&&
and_eq	&=
bitand	&
bitor	>
compl	~
not	!
not_eq	!=
or
or_eq	>=
xor	^
xor_eq	^=

C++

These identifiers are operator keywords

Operators in C and C++

This is a list of operators in the C and C++ programming languages. All the operators listed exist in C++; the fourth column "Included in C", dictates whether an operator is also present in C...

 in the ISO C++ programming language and do not require the inclusion of a header file. For consistency, the C++98 standard provides the header <ciso646>. However the latter file has no effect, being empty.