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(libc.info)Conversion Specifier Options

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Conversion Specifier Options
----------------------------

   If you define a meaning for `%A', what if the template contains
`%+23A' or `%-#A'?  To implement a sensible meaning for these, the
handler when called needs to be able to get the options specified in
the template.

   Both the HANDLER-FUNCTION and ARGINFO-FUNCTION accept an argument
that points to a `struct printf_info', which contains information about
the options appearing in an instance of the conversion specifier.  This
data type is declared in the header file `printf.h'.

 - Type: struct printf_info
     This structure is used to pass information about the options
     appearing in an instance of a conversion specifier in a `printf'
     template string to the handler and arginfo functions for that
     specifier.  It contains the following members:

    `int prec'
          This is the precision specified.  The value is `-1' if no
          precision was specified.  If the precision was given as `*',
          the `printf_info' structure passed to the handler function
          contains the actual value retrieved from the argument list.
          But the structure passed to the arginfo function contains a
          value of `INT_MIN', since the actual value is not known.

    `int width'
          This is the minimum field width specified.  The value is `0'
          if no width was specified.  If the field width was given as
          `*', the `printf_info' structure passed to the handler
          function contains the actual value retrieved from the
          argument list.  But the structure passed to the arginfo
          function contains a value of `INT_MIN', since the actual
          value is not known.

    `wchar_t spec'
          This is the conversion specifier character specified.  It's
          stored in the structure so that you can register the same
          handler function for multiple characters, but still have a
          way to tell them apart when the handler function is called.

    `unsigned int is_long_double'
          This is a boolean that is true if the `L', `ll', or `q' type
          modifier was specified.  For integer conversions, this
          indicates `long long int', as opposed to `long double' for
          floating point conversions.

    `unsigned int is_char'
          This is a boolean that is true if the `hh' type modifier was
          specified.

    `unsigned int is_short'
          This is a boolean that is true if the `h' type modifier was
          specified.

    `unsigned int is_long'
          This is a boolean that is true if the `l' type modifier was
          specified.

    `unsigned int alt'
          This is a boolean that is true if the `#' flag was specified.

    `unsigned int space'
          This is a boolean that is true if the ` ' flag was specified.

    `unsigned int left'
          This is a boolean that is true if the `-' flag was specified.

    `unsigned int showsign'
          This is a boolean that is true if the `+' flag was specified.

    `unsigned int group'
          This is a boolean that is true if the `'' flag was specified.

    `unsigned int extra'
          This flag has a special meaning depending on the context.  It
          could be used freely by the user-defined handlers but when
          called from the `printf' function this variable always
          contains the value `0'.

    `unsigned int wide'
          This flag is set if the stream is wide oriented.

    `wchar_t pad'
          This is the character to use for padding the output to the
          minimum field width.  The value is `'0'' if the `0' flag was
          specified, and `' '' otherwise.