(libc.info.gz) Integer Conversions

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 12.12.4 Integer Conversions
 ---------------------------
 
 This section describes the options for the '%d', '%i', '%o', '%u', '%x',
 and '%X' conversion specifications.  These conversions print integers in
 various formats.
 
    The '%d' and '%i' conversion specifications both print an 'int'
 argument as a signed decimal number; while '%o', '%u', and '%x' print
 the argument as an unsigned octal, decimal, or hexadecimal number
 (respectively).  The '%X' conversion specification is just like '%x'
 except that it uses the characters 'ABCDEF' as digits instead of
 'abcdef'.
 
    The following flags are meaningful:
 
 '-'
      Left-justify the result in the field (instead of the normal
      right-justification).
 
 '+'
      For the signed '%d' and '%i' conversions, print a plus sign if the
      value is positive.
 
 ' '
      For the signed '%d' and '%i' conversions, if the result doesn't
      start with a plus or minus sign, prefix it with a space character
      instead.  Since the '+' flag ensures that the result includes a
      sign, this flag is ignored if you supply both of them.
 
 '#'
      For the '%o' conversion, this forces the leading digit to be '0',
      as if by increasing the precision.  For '%x' or '%X', this prefixes
      a leading '0x' or '0X' (respectively) to the result.  This doesn't
      do anything useful for the '%d', '%i', or '%u' conversions.  Using
      this flag produces output which can be parsed by the 'strtoul'
      function ( Parsing of Integers) and 'scanf' with the '%i'
      conversion ( Numeric Input Conversions).
 
 '''
      Separate the digits into groups as specified by the locale
      specified for the 'LC_NUMERIC' category;  General Numeric.
      This flag is a GNU extension.
 
 '0'
      Pad the field with zeros instead of spaces.  The zeros are placed
      after any indication of sign or base.  This flag is ignored if the
      '-' flag is also specified, or if a precision is specified.
 
    If a precision is supplied, it specifies the minimum number of digits
 to appear; leading zeros are produced if necessary.  If you don't
 specify a precision, the number is printed with as many digits as it
 needs.  If you convert a value of zero with an explicit precision of
 zero, then no characters at all are produced.
 
    Without a type modifier, the corresponding argument is treated as an
 'int' (for the signed conversions '%i' and '%d') or 'unsigned int' (for
 the unsigned conversions '%o', '%u', '%x', and '%X').  Recall that since
 'printf' and friends are variadic, any 'char' and 'short' arguments are
 automatically converted to 'int' by the default argument promotions.
 For arguments of other integer types, you can use these modifiers:
 
 'hh'
      Specifies that the argument is a 'signed char' or 'unsigned char',
      as appropriate.  A 'char' argument is converted to an 'int' or
      'unsigned int' by the default argument promotions anyway, but the
      'h' modifier says to convert it back to a 'char' again.
 
      This modifier was introduced in ISO C99.
 
 'h'
      Specifies that the argument is a 'short int' or 'unsigned short
      int', as appropriate.  A 'short' argument is converted to an 'int'
      or 'unsigned int' by the default argument promotions anyway, but
      the 'h' modifier says to convert it back to a 'short' again.
 
 'j'
      Specifies that the argument is a 'intmax_t' or 'uintmax_t', as
      appropriate.
 
      This modifier was introduced in ISO C99.
 
 'l'
      Specifies that the argument is a 'long int' or 'unsigned long int',
      as appropriate.  Two 'l' characters is like the 'L' modifier,
      below.
 
      If used with '%c' or '%s' the corresponding parameter is considered
      as a wide character or wide character string respectively.  This
      use of 'l' was introduced in Amendment 1 to ISO C90.
 
 'L'
 'll'
 'q'
      Specifies that the argument is a 'long long int'.  (This type is an
      extension supported by the GNU C compiler.  On systems that don't
      support extra-long integers, this is the same as 'long int'.)
 
      The 'q' modifier is another name for the same thing, which comes
      from 4.4 BSD; a 'long long int' is sometimes called a "quad" 'int'.
 
 't'
      Specifies that the argument is a 'ptrdiff_t'.
 
      This modifier was introduced in ISO C99.
 
 'z'
 'Z'
      Specifies that the argument is a 'size_t'.
 
      'z' was introduced in ISO C99.  'Z' is a GNU extension predating
      this addition and should not be used in new code.
 
    Here is an example.  Using the template string:
 
      "|%5d|%-5d|%+5d|%+-5d|% 5d|%05d|%5.0d|%5.2d|%d|\n"
 
 to print numbers using the different options for the '%d' conversion
 gives results like:
 
      |    0|0    |   +0|+0   |    0|00000|     |   00|0|
      |    1|1    |   +1|+1   |    1|00001|    1|   01|1|
      |   -1|-1   |   -1|-1   |   -1|-0001|   -1|  -01|-1|
      |100000|100000|+100000|+100000| 100000|100000|100000|100000|100000|
 
    In particular, notice what happens in the last case where the number
 is too large to fit in the minimum field width specified.
 
    Here are some more examples showing how unsigned integers print under
 various format options, using the template string:
 
      "|%5u|%5o|%5x|%5X|%#5o|%#5x|%#5X|%#10.8x|\n"
 
      |    0|    0|    0|    0|    0|    0|    0|  00000000|
      |    1|    1|    1|    1|   01|  0x1|  0X1|0x00000001|
      |100000|303240|186a0|186A0|0303240|0x186a0|0X186A0|0x000186a0|
 

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