NAME
ParseArgv - process command-line options

SYNOPSIS
#include <ParseArgv.h>

int
ParseArgv(argcPtr, argv, argTable, flags)

ARGUMENTS
Pointer to number of arguments in argv; gets modified to hold number of unprocessed arguments that remain after the call. Command line arguments passed to main program. Modified to hold unprocessed arguments that remain after the call. Array of argument descriptors, terminated by element with type ARGV_END. If non-zero, then it specifies one or more flags that control the parsing of arguments. Different flags may be OR'ed together. The flags currently defined are ARGV_DONT_SKIP_FIRST_ARG, ARGV_NO_ABBREV, ARGV_NO_LEFTOVERS, ARGV_NO_DEFAULTS and ARGV_NO_PRINT.

DESCRIPTION

ParseArgv processes an array of command-line arguments according to a table describing the kinds of arguments that are expected. Each of the arguments in argv is processed in turn: if it matches one of the entries in argTable, the argument is processed according to that entry and discarded. The arguments that do not match anything in argTable are copied down to the beginning of argv (retaining their original order) and returned to the caller. At the end of the call ParseArgv sets *argcPtr to hold the number of arguments that are left in argv, and argv[*argcPtr] will hold the value NULL. Normally, ParseArgv assumes that argv[0] is a command name, so it is treated like an argument that doesn't match argTable and returned to the caller; however, if the ARGV_DONT_SKIP_FIRST_ARG bit is set in flags then argv[0] will be processed just like the other elements of argv.

ParseArgv normally returns the value FALSE (0). If an error occurs while parsing the arguments, then TRUE (1) is returned and ParseArgv will print an error message on stderr. In the event of an error return, *argvPtr will not have been modified, but argv could have been partially modified. The possible causes of errors are explained below.

The argTable array specifies the kinds of arguments that are expected; each of its entries has the following structure:

    typedef struct {
        char	*key;
        int	type;
        char	*src;
        char	*dst;
        char	*help;
    } ArgvInfo;

The key field is a string such as ``-display'' or ``-bg'' that is compared with the values in argv. Type indicates how to process an argument that matches key (more on this below). Src and dst are additional values used in processing the argument. Their exact usage depends on type, but typically src indicates a value and dst indicates where to store the value. The char * declarations for src and dst are placeholders: the actual types may be different. Lastly, help is a string giving a brief description of this option; this string is printed when users ask for help about command-line options.

When processing an argument in argv, ParseArgv compares the argument to each of the key's in argTable. ParseArgv selects the first specifier whose key matches the argument exactly, if such a specifier exists. Otherwise ParseArgv selects a specifier for which the argument is a unique abbreviation. If the argument is a unique abbreviation for more than one specifier, then an error is returned. If there is no matching entry in argTable, then the argument is skipped and returned to the caller.

Once a matching argument specifier is found, ParseArgv processes the argument according to the type field of the specifier. The argument that matched key is called ``the matching argument'' in the descriptions below. As part of the processing, ParseArgv may also use the next argument in argv after the matching argument, which is called ``the following argument''. The legal values for type, and the processing that they cause, are as follows:

ARGV_END
    Marks the end of the table. The last entry in argTable must have this type; all of its other fields are ignored and it will never match any arguments.

ARGV_CONSTANT
    Src is treated as an integer and dst is treated as a pointer to an integer. Src is stored at *dst. The matching argument is discarded.

ARGV_INT
    The following argument must contain an integer string in the format accepted by strtol (e.g. ``0'' and ``0x'' prefixes may be used to specify octal or hexadecimal numbers, respectively). Dst is treated as a pointer to an integer; the following argument is converted to an integer value and stored at *dst. Src is treated as an integer count: if its value is greater than 1, then that many arguments are processed and Dst is treated as an array pointer. The matching and following arguments are discarded from argv.

ARGV_FLOAT
    The following argument must contain a floating-point number in the format accepted by strtol. Dst is treated as the address of an double-precision floating point value; the following argument is converted to a double-precision value and stored at *dst. Src is treated as an integer count: if its value is greater than 1, then that many arguments are processed and Dst is treated as an array pointer. The matching and following arguments are discarded from argv.

ARGV_STRING
    In this form, dst is treated as a pointer to a (char *); ParseArgv stores at *dst a pointer to the following argument, and discards the matching and following arguments from argv. Src is treated as an integer count: if its value is greater than 1, then that many arguments are processed and Dst is treated as an array pointer.

ARGV_HELP
    When this kind of option is encountered, ParseArgv uses the help fields of argTable to format a message describing all the valid arguments. The message is written on stderr and ParseArgv returns TRUE. When this happens, the caller normally aborts. If the key field of a ARGV_HELP specifier is NULL, then the specifier will never match any arguments; in this case the specifier simply provides extra documentation, which will be included when some other ARGV_HELP entry causes help information to be returned.

ARGV_REST
    This option is used by programs or commands that allow the last several of their options to be the name and/or options for some other program. If a ARGV_REST argument is found, then ParseArgv doesn't process any of the remaining arguments; it returns them all at the beginning of argv (along with any other unprocessed arguments). In addition, ParseArgv treats dst as the address of an integer value, and stores at *dst the index of the first of the ARGV_REST options in the returned argv. This allows the program to distinguish the ARGV_REST options from other unprocessed options that preceeded the ARGV_REST.

ARGV_FUNC
    For this kind of argument, src is treated as the address of a procedure, which is invoked to process the following argument. The procedure should have the following structure:

    int
    func(dst, key, nextArg)
        char	*dst;
        char	*key;
        char	*nextArg;
    {
    }

    The dst and key parameters will contain the corresponding fields from the argTable entry, and nextArg will point to the following argument from argv (or NULL if there aren't any more arguments left in argv). If func uses nextArg (so that ParseArgv should discard it), then it should return 1. Otherwise it should return 0 and TkParseArgv will process the following argument in the normal fashion. In either event the matching argument is discarded.

ARGV_GENFUNC
    This form provides a more general procedural escape. It treats src as the address of a procedure, and passes that procedure all of the remaining arguments. The procedure should have the following form:

    int
    genfunc(dst, key, argc, argv)
        char	*dst;
        char	*key;
        int	argc;
        char	**argv;
    {
    }

    The dst and key parameters will contain the corresponding fields from the argTable entry. Argc and argv refer to all of the options after the matching one. Genfunc should behave in a fashion similar to ParseArgv: parse as many of the remaining arguments as it can, then return any that are left by compacting them to the beginning of argv (starting at argv[0]). Genfunc should return a count of how many arguments are left in argv; ParseArgv will process them. If genfunc encounters an error then it should print an error message on stderr, and return -1; when this happens ParseArgv will abort its processing and return TRUE.

FLAGS

ARGV_DONT_SKIP_FIRST_ARG
    ParseArgv normally treats argv[0] as a program or command name, and returns it to the caller just as if it hadn't matched argTable. If this flag is given, then argv[0] is not given special treatment.

ARGV_NO_ABBREV
    Normally, ParseArgv accepts unique abbreviations for key values in argTable. If this flag is given then only exact matches will be acceptable.

ARGV_NO_LEFTOVERS
    Normally, ParseArgv returns unrecognized arguments to the caller. If this bit is set in flags then ParseArgv will return an error if it encounters any argument that doesn't match argTable. The only exception to this rule is argv[0], which will be returned to the caller with no errors as long as ARGV_DONT_SKIP_FIRST_ARG isn't specified.

ARGV_NO_DEFAULTS
    Normally, ParseArgv searches an internal table of standard argument specifiers in addition to argTable. If this bit is set in flags, then ParseArgv will use only argTable and not its default table.

ARGV_NO_PRINT
    Normally, ParseArgv prints error message on stderr. If this bit is set in flags, then ParseArgv will not print any error messages.

EXAMPLE

Here is an example definition of an argTable and some sample command lines that use the options. Note the effect on argc and argv; arguments processed by ParseArgv are eliminated from argv, and argc is updated to reflect reduced number of arguments.

    /*
     * Define and set default values for globals.
     */
    int debugFlag = 0;
    int numReps = 100;
    char defaultFileName[] = "out";
    char *fileName = defaultFileName;
    Boolean exec = FALSE;

    /*
     * Define option descriptions.
     */
    ArgvInfo argTable[] = {
    	{"-X", ARGV_CONSTANT, (char *) 1, (char *) &debugFlag,
    		"Turn on debugging printfs"},
    	{"-N", ARGV_INT, (char *) NULL, (char *) &numReps,
    		"Number of repetitions"},
    	{"-of", ARGV_STRING, (char *) NULL, (char *) &fileName,
    		"Name of file for output"},
    	{"x", ARGV_REST, (char *) NULL, (char *) &exec,
    		"File to exec, followed by any arguments (must be last argument)."},
    	{(char *) NULL, ARGV_END, (char *) NULL, (char *) NULL,
    	    (char *) NULL}
    };

    main(argc, argv)
    	int argc;
    	char *argv[];
    {
    	...

    	if (ParseArgv(&argc, argv, argTable, 0)) {
    		exit(1);
    	}

    	/*
    	 * Remainder of the program.
    	 */
    }

Note that default values can be assigned to variables named in argTable: the variables will only be overwritten if the particular arguments are present in argv. Here are some example command lines and their effects.

    prog -N 200 infile		# just sets the numReps variable to 200
    prog -of out200 infile 	# sets fileName to reference "out200"
    prog -XN 10 infile		# sets the debug flag, also sets numReps

In all of the above examples, argc will be set by ParseArgv to 2, argv[0] will be ``prog'', argv[1] will be ``infile'', and argv[2] will be NULL.

KEYWORDS
arguments, command line, options