Alternative operator representations (since C99)

 

C

Language

Standard Library

Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

C language

General topics
Preprocessor
Comments
Keywords
ASCII chart
Escape sequences
History of C
Flow control
Conditional execution statements
if statement	switch statement
Iteration statements
for loop	while loop do-while loop
Jump statements
continue statement break statement	goto statement return statement
Functions
function declaration
inline specifier
Types
fundamental types pointer types compound types enumeration types	union types function types
Specifiers
cv specifiers
storage-class specifiers
alignas specifier (C99)
function specifiers (C99)
Literals
integer literals character literals floating-point literals	string literals boolean literals(C99)
Expressions
order of evaluation
operators
operator precedence
alternative operators
Utilities
typedef declaration
attributes (C99)
casts
Miscellaneous
Inline assembly

 

C source code may be written in any non-ASCII 7-bit character set that includes the ISO 646:1983 invariant character set. However, several C operators and punctuators require characters that are outside of the ISO 646 codeset: {, }, [, ], #, \, ^, |, ~. To be able to use character encodings where some or all of these symbols do not exist (such as the German DIN 66003), there are two possibilities: alternative spellings of operators that use these characters or special combinations of two or three ISO 646 compatible characters that are interpreted as if they were a single non-ISO 646 character.

Alternative spellings

There are alternative spellings for several operators defined in <iso646.h>.

Defined in header <iso646.h>
Primary	Alternative
&&	and (macro constant)
&=	and_eq (macro constant)
&	bitand (macro constant)
|	bitor (macro constant)
~	compl (macro constant)
!	not (macro constant)
!=	not_eq (macro constant)
||	or (macro constant)
|=	or_eq (macro constant)
^	xor (macro constant)
^=	xor_eq (macro constant)

Digraphs and trigraphs

The following combinations of two and three characters (digraphs and trigraphs) are valid substitutions for their respective primary characters:

Primary	Digraph	Trigraph
{	<%	??<
}	%>	??>
[	<:	??(
]	:>	??)
#	%:	??=
\		??/
^		??'
|		??!
~		??-

Note that trigraphs (but not digraphs) are parsed before comments and string literals are recognized, so a comment such as // Will the next line be executed?????/ will effectively comment out the following line, and the string literal such as "What's going on??!" is parsed as "What's going on|".

Example

The following example demonstrates alternative operator spellings from the <iso646.h> header as well as use of digraphs and trigraphs:

run this code

%:include <stdlib.h>
%:include <stdio.h>
%:include <iso646.h>
 
int main(int argc, char** argv) ??<
 
  if (argc > 1 and argv<:1:> not_eq NULL) <%
    printf("Hello %s!\n", argv<:1:>);
  %>
 
  return EXIT_SUCCESS;
 
??>

Output:

(if the first command line argument to the compiled executable - argv[1] - is "monkeys")
 
Hello monkeys!