Constants

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Constants or literals are tokens representing fixed numeric or character values. The terms "constant" and "literal" are used interchangeably here.

The compiler supports the following classes of constants: integer, floating point, character and string, boolean, and enumeration.

Internal representation of numerical types shows how these types are represented internally in a processor architecture.

The data type of a constant is deduced by the compiler using such clues as numeric value and the format used in the source code. The formal definition of a constant is shown in the following table.

Constants: Formal Definitions: 

constant:
  floating-constant
  integer-constant
  character-constant
  string-literal
  enumeration-constant
  boolean-literal 

enumeration-constant:
  identifier

 floating-constant:
  fractional-constant <exponent-part> <floating-suffix>
  digit-sequence exponent-part <floating-suffix>

 character-constant:
   'c-char-sequence'     (char - ANSI)
   L'c-char-sequence'    (wchar_t - Widestring)
   u'c-char-sequence'    (char16_t - UTF-16) (С++0x)
   U'c-char-sequence'    (char32_t - UTF-32) (С++0x)

fractional-constant:
  <digit-sequence>  . digit-sequence
  digit-sequence  . 

c-char-sequence:
  c-char
  c-char-sequence c-char

exponent-part:
  e <sign> digit-sequence
  E <sign> digit-sequence

c-char:
  Any character in the source character set except
    the single-quote ( ' ), 
    backslash ( \ ),
    or newline character 
  escape-sequence

sign: one of
  + -

escape-sequence:  
  simple-escape-sequence
  octal-escape-sequence
  hexadecimal-escape-sequence

digit-sequence:
  digit
  digit-sequence digit

simple-escape-sequence: one of 
  \" \' \? \\
  \a \b \f \n \r \t \v

floating-suffix: one of
  f l F L

octal-escape-sequence:
  \ octal-digit   (\o)
  \ octal-digit octal-digit   (\oo)
  \ octal-digit octal-digit octal-digit   (\ooo)

 integer-constant:
  decimal-constant <integer-suffix>
  octal-constant <integer-suffix>
  hexadecimal-constant <integer-suffix>

hexadecimal-escape-sequence:
  \x hexadecimal-digit   (\xh)
  \X hexadecimal-digit   (\Xh)
  hexadecimal-escape-sequence hexadecimal-digit

decimal-constant:
  nonzero-digit
  decimal-constant digit

 string-literal:
   "s-char-sequence"     (char* - ANSI)
   L"s-char-sequence"    (wchar_t* - Widestring)
   u"s-char-sequence"    (char16_t* - UTF-16) (С++0x)
   U"s-char-sequence"    (char32_t* - UTF-32) (С++0x)

octal-constant:
  0
  octal-constant octal-digit

s-char-sequence:
  s-char
  s-char-sequence s-char

hexadecimal-constant:
  0x hexadecimal-digit
  0X hexadecimal-digit
  hexadecimal-constant hexadecimal-digit

s-char:
  Any character in the source character set except
    the double-quote ( " ), 
    backslash ( \ ),
    or newline character 
  escape-sequence

nonzero-digit: one of
  1 2 3 4 5 6 7 8 9

 boolean-literal:
  true
  false

octal-digit: one of
  0 1 2 3 4 5 6 7

hexadecimal-digit: one of
  0 1 2 3 4 5 6 7 8 9
  a b c d e f
  A B C D E F

integer-suffix:
  unsigned-suffix <long-suffix>
  long-suffix <unsigned-suffix>
  <unsigned-suffix> size-suffix 

unsigned-suffix: one of
  u U

long-suffix: one of
  l L 

 size-suffix: one of
  i8 I8 i16 I16  i32 I32 i64 I64

See Also

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