VistaIOIdentifyFiles(3)
NAME
VistaIOIdentifyFiles - identify files specified by command line arguments
SYNOPSIS
#include <vistaio.h>
VistaIOBoolean VistaIOIdentifyFiles (noptions, options, keyword, argc, argv, fd)
int noptions;
VistaIOOptionDescRec options[noptions];
VistaIOStringConst keyword;
int *argc;
char *argv;
int fd;
ARGUMENTS
noptions Specifies the number of entries in the table of option
descriptors.
options Specifies the location of the table of option descriptors.
keyword Specifies the option keyword that is used on the command line
to specify filenames.
argc Specifies the number of command line arguments to be parsed,
and returns the number of arguments that were not recognized
as valid filenames.
argv Specifies a vector of command line arguments to be parsed,
and returns a vector of the arguments that were not
recognized as valid filenames.
fd May specify an open file descriptor that should be checked to
ensure it corresponds to a file or pipe if no filenames are
explicitly given by command line arguments. Or it may be -1
to indicate that no such checking should be done.
DESCRIPTION
By convention, a Vista program that reads one or more files can be told
of those files in any of three ways:
(a) the filenames can be supplied as arguments to a command line
option (e.g., vxview -in file1 file2 ...);
(b) the filenames can be supplied as command line arguments not
associated with any particular option (e.g.,
vxview file1 file2 ...); or
(c) a file can be directed to the program's standard input stream
(e.g., vxview < file1).
In parsing a command's arguments, these alternatives are considered in
order. That is, first the program looks for an appropriate command line
option (e.g., -in). If no such option has been specified, it checks for
command line arguments not associated with any option. If those are
also absent, it tries to read its file from the standard input stream.
Similarly, an output file may be specified using a command line option
(e.g., vconvolve -out file1), or, by omitting the option and directing
the program's standard output stream (e.g., vconvolve > file1).
VistaIOIdentifyFiles identifies a program's input files or output files
according to this convention. It is called after VistaIOParseCommand(3)
has parsed any command line arguments that can be identified as
options, leaving the remaining arguments in *argc and argv.
VistaIOIdentifyFiles is then called once to identify any input files,
and perhaps again to identify an output file.
The noptions and options parameters specify the table used earlier by
VistaIOParseCommand to parse command line options. (See
VistaIOoption(3) for details.) The argc and argv parameters specify a
list of command line arguments that VistaIOParseCommand has returned as
unparsed (including the program's name, which should be first in this
list). The keyword parameter specifies the command line option that may
be used to specify filenames (e.g., ``in'' or ``out''), absent any
``-'' prefix. The entry in the option table for the option specified by
keyword must (a) refer to a ``found'' flag that VistaIOParseCommand can
use to record whether or not the option is present on the command line,
and (b) refer to a location where the option's arguments can be stored.
VistaIOIdentifyFiles consults the ``found'' flag to determine whether
the option was present on the command line. If it was,
VistaIOIdentifyFiles returns immediately. Otherwise, it then examines
*argc to determine whether an appropriate number of unparsed command
line arguments exist. If there are a sufficient number of arguments
present, they are interpreted as filenames and stored at the location
indicated by the option table entry
Finally, if no filenames are found either as arguments to a -keyword
option or as additional command line arguments, VistaIOIdentifyFiles
considers the possibility that a file has been attached to a file
descriptor such as the standard input or output stream. You may wish to
ensure that a file is allowed to default to one of these streams only
if the stream has been associated with a file or pipe, and not a
terminal. In that case, pass as fd the file descriptor that will serve
as the default source or destination of the file, and
VistaIOIdentifyFiles will check that it is indeed associated with a
file or pipe. Otherwise, pass -1 for fd and it will not perform this
check.
RETURN VALUES
VistaIOIdentifyFiles returns TRUE if it finds one or more files specified on the command line, and if the number of files specified is compatible with the number field of the option table entry. It returns FALSE if no files were specified, if the wrong number of files were specified, or if the file would default to a file descriptor but the file descriptor fd is not associated with a file or pipe. On successful return VistaIOIdentifyFiles will have eliminated, from the list represented by *argc and argv, any command line arguments that it identified as filenames. Also, the filenames found will be stored at the location indicated by the option table entry for keyword. A default to the standard input or output stream will be identified by a filename of ``-''.
EXAMPLE
The following fragment is drawn from a program that reads one or more
files and writes a single file. The input files may be specified with a
-in option, as extra command line arguments, or by being directed to
the standard input stream. The output file may be specified with a -out
option, and, if that option is not present, the file will be written to
the standard output stream regardless of whether it is associated with
a file or a terminal.
VistaIOArgVector in_filenames;
VistaIOStringConst out_filename;
VistaIOBoolean in_found, out_found;
VistaIOOptionDescRec options[] = {
{ "in", VistaIOStringRepn, 0, & in_filenames, & in_found,
NULL, "Input file(s)" },
{ "out", VistaIOStringRepn, 1, & out_filename, & out_found,
NULL, "Output file" }
};
main (int argc, char *argv)
{
/* Parse command line options: */
if (! VistaIOParseCommand (VistaIONumber (options), options,
& argc, argv)) {
Usage: VistaIOReportUsage (argv[0], VistaIONumber (options), options,
"file1 file2...");
exit (1);
}
/* Identify input file(s): */
if (! VistaIOIdentifyFiles (VistaIONumber (options), options, "in",
& argc, argv, 0))
goto Usage;
/* Any remaining unparsed arguments are erroneous: */
if (argc > 1) {
VistaIOReportBadArgs (argc, argv);
goto Usage;
}
/* Identify output file: */
if (! VistaIOIdentifyFiles (VistaIONumber (options), options, "out",
& argc, argv, -1))
goto Usage;
/* Open and process each input file: */
for (i = 0; i < in_filenames.number; i++) {
filename = ((VistaIOStringConst *) in_filename.vector)[i];
if (strcmp (filename, "-") != 0) {
f = fopen (filename, "r");
if (f == NULL)
VistaIOError ("Unable to open file \"%s\"", filename);
} else f = stdin;
...
}
}
SEE ALSO
VistaIOOpenFile(3), VistaIOParseCommand(3), VistaIOReportBadArgs(3), VistaIOReportUsage(3), VistaIOoption(3),
DIAGNOSTICS
VistaIOIdentifyFiles reports errors in command line options by printing
directly to the standard error stream. Error reports include the
program name obtained from argv[0]. The following messages may be
produced:
``n files must be specified by -keyword or extra command arguments''
The program requires that n files be specified (n > 1). Neither
a -keyword option was present on the command line, nor were
there at least n unparsed arguments that could be interpreted as
filenames.
``No file specified by -keyword, extra command argument, or <''
The program requires that at least one file be specified, and it
can be specified in any of three ways. However, it wasn't
specified in any form.
In addition, VistaIOIdentifyFiles may invoke VistaIOError with the
following messages:
``Option -keyword not defined in option table''
The keyword parameter specified a keyword not defined in the
option table.
``No value storage for option -keyword''
The keyword parameter specifies an option table entry whose
value field is NULL
``No "found" flag for option -keyword''
The keyword parameter specifies an option table entry whose
found field doesn't point to a dedicated VistaIOBoolean
variable.
``Failed to fstat() fd fd''
An fstat() call failed on the supplied file descriptor, fd.
AUTHOR
Art Pope <pope@cs.ubc.ca> Adaption to vistaio: Gert Wollny <gw.fossdev@gmail.com>
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