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>