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SCANARGS(3)		   Library Functions Manual		   SCANARGS(3)

NAME
       scanargs, qscanargs - formatted conversion from command argument	list

SYNOPSIS
       #include	<stdio.h>

       scanargs(argc, argv, format [, pointer]...  )
       int argc;
       char *argv[];
       char *format;

DESCRIPTION
       Scanargs	reads argc arguments from an argument list pointed to by argv.
       It converts the argument	list  according	 to  the  format  string,  and
       stores the results of the conversions in	its parameters.

       Scanargs	expects	as its parameters an argument count argc, a pointer to
       an argument list	argv (see exec(2)), a control string format, described
       below,  and  a  set of pointer arguments	indicating where the converted
       output should be	stored.

       The control string contains specifications, which are  used  to	direct
       interpretation of argument sequences.  It contains the necessary	infor-
       mation to describe an acceptable	syntax for the argument	list, and  the
       expected	meaning	of each	argument.

       If  the	scanning  fails	it will	print a	cryptic	message	telling	why it
       failed, and generate a usage message from the control string.

       The control string is composed of two parts:

       Name: The first characters in the string	are assumed to be the  calling
       name  of	the program being executed. This is used for generation	of us-
       age messages, but is otherwise ignored.	If this	field is a % sign,  it
       is replaced with	the contents of	argv[0]	in the message.

       Conversions: Following  the name, an optional list of conversion	speci-
       fications is given, with	separating spaces.  The	structure of a conver-
       sion specification:

	      label_key_conversion

       consists	 of a label which is a string of non-space characters describ-
       ing the acceptable argument, a key which	may be either of

       %   The argument	is optional. Its absence is ignored.

       !   A required argument.	If absent, an error return ensues.

       The conversion character	indicates the interpretation of	the  argument;
       the corresponding pointer parameter must	be of a	restricted type.

       The following conversion	characters are supported:

       d D a  decimal  integer is expected; the	corresponding parameter	should
	   be an int or	a long (if D is	specified) pointer.

       o O an octal integer is expected; the corresponding parameter should be
	   an int or a long pointer.

       x X a  hexadecimal  integer  is	expected;  the corresponding parameter
	   should be an	int or a long pointer.

       n N an integer numeric conversion using C language syntax.  Numbers be-
	   ginning  0x	are  hexadecimal,  numbers  beginning 0	are octal, and
	   other numbers are decimal.  Negative	hex numbers must have the  mi-
	   nus	sign  following	 the  0x,  i.e.	negative 0xa would be given as
	   0x-a.  The corresponding pointer should point to an int or a	long.

       f F a floating point number is expected;	 the  corresponding  parameter
	   should be a pointer to a float or a double.

       s   a  character	string is expected; the	corresponding parameter	should
	   be the address of a pointer to char.

       -   a single character flag is expected;	 the  corresponding  parameter
	   should  be  an  int pointer.	 The occurrence	of a - followed	by the
	   character specified in the label will  cause	 the  setting  of  the
	   least  significant bit of the integer pointed to by the correspond-
	   ing parameter.  The label may consist of up to  sixteen  (actually,
	   up  to  the	number	of bits	in an int) option characters, in which
	   case	one of the bits	of the integer is independently	set to reflect
	   which  one of the flags was present.	(The right most	character cor-
	   responds to the LSB of the integer)	Only one option	may be	chosen
	   from	 each  conversion  specification.   The	bits which are not set
	   will	remain in their	previous state.	 For example, a	 specification
	   of  abc%-  would match one of -a -b or -c in	the argument list.  -c
	   would cause the corresponding variable to be	set to 1, -b to	2, and
	   -a  to  4.  (Actually, these	bits would be ored in, but assuming an
	   initial value of 0, this is true).

	   The - may be	 followed  immediately	by  more  label_key_conversion
	   specifications.  These should not be	separated by blanks and	should
	   not contain any - specifications.  They will	be processed  only  if
	   the	flag  argument is scanned.  This allows	optional specification
	   of parameters corresponding to a flag (e.g.	 -f  file  ).	Corre-
	   sponding arguments on the command line must appear between the flag
	   which introduces them and the next flag in the command line.

       $   This	may appear only	as the last specifier in  the  format  string,
	   and	is  used  to  "eat up" the rest	of the command arguments.  The
	   corresponding function argument is an int pointer.  An  index  into
	   argv	 to  the  dividing point between the arguments which have been
	   used, and those which have not is returned.	This index  points  to
	   the	first  unused  command argument.  If there is no such dividing
	   point, an error will	be generated (but $ may	match zero  arguments,
	   as long as the entire set of	arguments has already been matched).

       A  string or numeric conversion character may be	preceded by a `*' or a
       `,' to indicate that a list of such arguments is	expected.  If  `,'  is
       used,  then the AT&T proposed argument standard is followed, and	a sin-
       gle string is expected, with the	individual list	elements separated  by
       commas  or spaces.  Two commas in a row will produce a null entry (0 if
       numeric,	zero-length string if string conversion), but multiple spaces,
       and  spaces following a comma, are taken	as a single separator.	If `*'
       is specified, then multiple arguments are parsed	to produce  the	 list.
       A  format specifier with	a `*' or a `,' takes two arguments.  The first
       is an int pointer, the number of	items in the list  is  returned	 here.
       The  second  is	a  pointer to pointer to the correct data type for the
       format specifier.  A pointer to the list	of arguments is	returned here.

       The scanner will	process	the control string from	 left  to  right,  and
       where there are multiple	conversions of the same	type, they will	be as-
       signed one to one with their order of occurrence	in the argument	 list.
       Where  the  order  of  the  arguments  is  not ambiguous	in the control
       string, they may	occur in any order in the argument list. (ie. A	 deci-
       mal  number  will not be	confused with a	flag, but may be confused with
       an octal	number or another decimal number. So if	an octal and a decimal
       number  are  to	be arguments, their order will determine their conver-
       sion, while a decimal number and	a flag as arguments may	occur  in  any
       order and still be converted correctly.)

       An  argument  list  that	does not match the requirements	of the control
       string will cause the printing of a short message telling  why,	and  a
       message	telling	what the correct usage is.  This usage is gleaned from
       the control string, and the  labels  are	 used  directly.   The	labels
       should  be  both	 terse and descriptive!	 Spaces, tabs, and newlines in
       the format string will be reproduced in the usage message, and  can  be
       used  for effective prettyprinting.  A single tab (following a newline)
       will indent the line directly under the command name in the usage  mes-
       sage.

       The  scanargs function returns 1	when the argument list matched the re-
       quirements of the control string, and returns 0 if there	was a failure.
       Parameters for any conversions not matched are left untouched.
       For example, the	call

	      int i; double x; char *name;
	      scanargs(argc, argv, "% decimal%d	floating%F file%s",
	       &i, &x, &name );

       in a C program executed by the shell command

	      %	program	10 3.5397 inputfile

       will  assign to i the value 10, x the value 3.5397, and name will point
       to the string "inputfile".

       If the program was executed by the shell	command

	      %	program	 3.4 .7	inputfile

       the following would be printed on the standard error:

	      extra arguments not processed
	      usage : program [decimal]	[floating] [file]

       because 3.4 matches the type of 'floating' and .7 matches the  type  of
       'file', leaving inputfile unmatched.

       Finally,	executing the command
	      %	program	10
       would assign 10 to i, leaving x and name	unaffected.

       This call could be used for the diff(1) command

	      int blanks; int flags; char *file1; char *file2;
	      scanargs(argc, argv, "diff b%- efh%- file1!s file2!s",
	       &blanks,	&flags,	&file1,	&file2 );

       and  would  only	allow one of either -e,	-f, or -h to be	chosen option-
       ally, with -b as	an independent option.	File1 and file2	are  both  re-
       quired.	The usage message for this version of diff would be

	      usage : diff [-b]	-{efh} file1 file2

       This call could be used for a simplified	version	of the sed(1) command

	      int efile; int noprint; char *script;
	      char *file1; char	*file2;
	      scanargs(argc, argv,
	       "sed n%-	f%-editfile!s script%s file%s",
	       &noprint, &efile, &file1, &script, &file2 );

       If  the	-f  option is specified, then a	file name must be given	as the
       next string argument.  The usage	message	for this version of sed	 would
       be

	      usage : sed [-n] [-f editfile] [script] file

       Further notes on	putting	together a format string:

       It  is possible for conditional arguments to be confused	with arguments
       which stand alone.  For this reason, it is recommended that  all	 flags
       (and  associated	 conditional arguments)	be specified first in the sca-
       nargs format string.  This ordering is not necessary  for  the  command
       line  arguments,	however.  The only case	which could still cause	confu-
       sion if these rules are followed	is illustrated below:
	      format string: "prog d%-num%d othernum%d"
	      command line:  prog -d 9
       It is unclear whether the number	9 should be associated	with  the  num
       parameter  or  the  othernum parameter.	Scanargs assigns it to the num
       parameter.  To force it to be  associated  with	othernum  the  command
       could be	invoked	as either
			prog 9 -d
	      or	prog -d	-- 9
       The  --	in the second example is interpreted as	a flag,	thereby	termi-
       nating the scan for arguments introduced	by the -d.  According  to  the
       proposed	 standard, an argument of -- is	to be interpreted as terminat-
       ing the optional	arguments on a flag.

       Note that if the	format string in the above example were
			"prog othernum%d d%-num%d"
       it would	be impossible to assign	a value	to num without also  assigning
       a value to othernum.  A command line of
		   prog	-d 9
       would match othernum with 9, leaving nothing to match num.

SEE ALSO
       exec(2),	scanf(3S)

DIAGNOSTICS
       Returns 0 on error, 1 on	success.

AUTHOR
       Gary Newman -- Ampex Corporation
       Spencer W. Thomas -- University of Utah

BUGS
       By  its nature a	call to	scanargs defines a syntax which	may be ambigu-
       ous, and	although the results may be surprising,	they  are  quite  pre-
       dictable.

				    7/23/90			   SCANARGS(3)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | DIAGNOSTICS | AUTHOR | BUGS

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