使用getopt_long()从命令行获取参数

众所周知，C程序的主函数有两个参数，其中，第一个参数是整型，可以获得包括程序名字的参数个数，第二个参数是字符数组指针或字符指针的指针，可以按顺序获得命令行上各个字符串参数。其原形是：

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

或者

int main(int argc, char **argv);

 

如果有一个解析CDR的程序，名叫destroy，负责将一个二进制格式的CDR文件转换为文本文件，输出的文本的样式由另外一个描述文件定义，那么，命令行要求输入的参数就有三个：CDR文件名、输出文件名和描述文件名。其中，前两个参数是必须输入的，第三个的描述文件名可以不输入，程序会自动采用默认的输出样式。很自然，主函数的三个参数就应该这样排列：

./destroy cdr cdr.txt [cdr.desc]

 

这样做在一般情况下不会有太大问题，问题来源于扩展性的需求。如果有一天，用户要求解析程序能够按关键字解析，只有含有关键字的CDR才能够输出。解决方法很简单，只要在参数列表的最后，加上它就可以了。不过，这样就使得原本可选的描述文件名变为必须输入：

./destroy cdr cdr.txt cdr.desc [keyword]

 

因为不改的话，你就不知道，第三个参数究竟是描述文件名，还是关键字。现在还算好办，如果以后陆续有增加参数的需求，关键字也变成必须输入了，这个时候，如果要查找全部CDR，你还得定义一个“特殊的关键字”，告诉程序，把数据统统给我捞出来……

 

有鉴于此，在Unix/Linux的正式的项目上，程序员通常会使用getopt()或者getopt_long()来获得输入的参数。两者的一个区别在于getopt()只支持短格式参数，而getopt_long()既支持短格式参数，又支持长格式参数。

短格式：./destroy -f cdr -o cdr.txt -c cdr.desc -k 123456

长格式：./destroy --file cdr --output cdr.txt --config cdr.desc --keyword 123456

 

引入了getopt()和getopt_long()的项目，设计者可以按需要，方便地增加参数，或者随意地放置参数的先后次序，只需要在程序中判断，哪些参数是必须的就可以了。关于这两个函数的用法，大家可以上网搜索一下，不再累述。附件destroy_linux.c给出了在Linux下使用getopt_long()的实例。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <getopt.h>

void print_usage(const char *program_name) {
	printf("%s 1.0.0 (2010-06-13)/n", program_name);
	printf("This is a program decoding a BER encoded CDR file/n");
	printf("Usage: %s -f <file_name> -o <output_name> [-c <config_name>] [-k <keyword>]/n", program_name);
	printf("    -f --file       the CDR file to be decoded/n");
	printf("    -o --output     the output file in plain text format/n");
	printf("    -c --config     the description file of the CDR file, if not given, use default configuration/n");
	printf("    -k --keyword    the keyword to search, if not given, all records will be written into output file/n");
}

int main(int argc, char *argv[]) {
	char *file_name = NULL;
	char *output_name = NULL;
	char *config_name = NULL;
	char *keyword = NULL;

	const char *short_opts = "hf:o:c:k:";
	const struct option long_opts[] = {
		{"help", no_argument, NULL, 'h'},
		{"file", required_argument, NULL, 'f'},
		{"output", required_argument, NULL, 'o'},
		{"config", required_argument, NULL, 'c'},
		{"keyword", required_argument, NULL, 'k'},
		{0, 0, 0, 0}
	};
	int hflag = 0;

	int c;
	opterr = 0;

	while ( (c = getopt_long(argc, argv, short_opts, long_opts, NULL)) != -1 ) {
		switch ( c ) {
			case 'h' :
				hflag = 1;
				break;
			case 'f' :
				file_name = optarg;
				break;
			case 'o' :
				output_name = optarg;
				break;
			case 'c' :
				config_name = optarg;
				break;
			case 'k' :
				keyword = optarg;
				break;
			case '?' :
				if ( optopt == 'f' || optopt == 'o' || optopt == 'c' || optopt == 'k' )
					printf("Error: option -%c requires an argument/n", optopt);
				else if ( isprint(optopt) )
					printf("Error: unknown option '-%c'/n", optopt);
				else
					printf("Error: unknown option character '//x%x'/n", optopt);
				return 1;
			default :
				abort();
		}
	}

	if ( hflag || argc == 1 ) {
		print_usage(argv[0]);
		return 0;
	}
	if ( !file_name ) {
		printf("Error: file name must be specified/n");
		return 1;
	}
	if ( !output_name ) {
		printf("Error: output name must be specified/n");
		return 1;
	}

	// if not setting default, Linux OK, but SunOS core dump
	if ( !config_name ) config_name = "(null)";
	if ( !keyword ) keyword = "(null)";
	printf("Parameters got: file_name = %s, output_name = %s, config_name = %s, keyword = %s/n", file_name, output_name, config_name, keyword);
	return 0;
}

另外一个区别是，getopt()几乎通用于所有类Unix系统，而getopt_long()只有在GNU的Unix/Linux下才能用。如果把上述程序放到Tru64上编译，就会出现以下错误：

cc -o destroy destroy_linux.c

cc: Error: destroy_linux.c, line 24: In the initializer for long_opts, an array's element type is incomplete, which precludes its initialization. (incompelinit)

                {"help", no_argument, NULL, 'h'},

----------------^

 

所以，如果一定要在Tru64等非GNU的OS上做到长格式的效果，除了自己另起炉灶之外，基本上只好借助一些跨平台的开源项目了。附件里的getopt_long.c和getopt.h是从opensolaris的网站上抄下来的，是包含在sg3_utils软件包中的程序。sg3_utils具体是什么，我也不知道，据说是一个Linux的开发包，用来直接使用SCSI命令集访问设备。（sg3_utils is a package of utilities for accessing devices that use SCSI command sets.）反正拿来能用就是了！

/*	$NetBSD: getopt.h,v 1.7 2005/02/03 04:39:32 perry Exp $	*/

/*-
 * Copyright (c) 2000 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Dieter Baron and Thomas Klausner.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *        This product includes software developed by the NetBSD
 *        Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * modified May 12, 2005 by Jim Basney <[email protected]>
 *
 * removed #include of non-POSIX <sys/cdefs.h> and <sys/featuretest.h>
 * removed references to _NETBSD_SOURCE and HAVE_NBTOOL_CONFIG_H
 * added #if !HAVE_GETOPT_LONG
 * removed __BEGIN_DECLS and __END_DECLS
 */

#ifndef _MYPROXY_GETOPT_H_
#define _MYPROXY_GETOPT_H_

#if !HAVE_GETOPT_LONG

#include <unistd.h>

/*
 * Gnu like getopt_long() and BSD4.4 getsubopt()/optreset extensions
 */
#define no_argument        0
#define required_argument  1
#define optional_argument  2

extern char *optarg;
extern int optind;
extern int optopt;
extern int opterr;

struct option {
	/* name of long option */
	const char *name;
	/*
	 * one of no_argument, required_argument, and optional_argument:
	 * whether option takes an argument
	 */
	int has_arg;
	/* if not NULL, set *flag to val when option found */
	int *flag;
	/* if flag not NULL, value to set *flag to; else return value */
	int val;
};

int getopt_long(int, char * const *, const char *,
    const struct option *, int *);
 
#endif /* !HAVE_GETOPT_LONG */

#endif /* !_MYPROXY_GETOPT_H_ */

/*	$NetBSD: getopt_long.c,v 1.17 2004/06/20 22:20:15 jmc Exp $	*/

/*-
 * Copyright (c) 2000 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Dieter Baron and Thomas Klausner.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *        This product includes software developed by the NetBSD
 *        Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * modified May 12, 2005 by Jim Basney <[email protected]>
 *
 * removed #include of non-POSIX <sys/cdefs.h> <err.h>
 * removed #include of "namespace.h"
 * use local "port_getopt.h" instead of <getopt.h>
 * removed REPLACE_GETOPT and HAVE_NBTOOL_CONFIG_H sections
 * removed __P() from function declarations
 * use ANSI C function parameter lists
 * removed optreset support
 * replace _DIAGASSERT() with assert()
 * replace non-POSIX warnx(...) with fprintf(stderr, ...)
 * added extern declarations for optarg, optind, opterr, and optopt
 */

#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: getopt_long.c,v 1.17 2004/06/20 22:20:15 jmc Exp $");
#endif /* LIBC_SCCS and not lint */

#include <assert.h>
#include <errno.h>
#include "getopt.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#ifdef __weak_alias
__weak_alias(getopt_long,_getopt_long)
#endif

#if !HAVE_GETOPT_LONG
#define IGNORE_FIRST	(*options == '-' || *options == '+')
#define PRINT_ERROR	((opterr) && ((*options != ':') /
				      || (IGNORE_FIRST && options[1] != ':')))
#define IS_POSIXLY_CORRECT (getenv("POSIXLY_CORRECT") != NULL)
#define PERMUTE         (!IS_POSIXLY_CORRECT && !IGNORE_FIRST)
/* XXX: GNU ignores PC if *options == '-' */
#define IN_ORDER        (!IS_POSIXLY_CORRECT && *options == '-')

/* return values */
#define	BADCH	(int)'?'
#define	BADARG		((IGNORE_FIRST && options[1] == ':') /
			 || (*options == ':') ? (int)':' : (int)'?')
#define INORDER (int)1

#define	EMSG	""

extern char *optarg;
extern int optind, opterr, optopt;

static int getopt_internal (int, char * const *, const char *);
static int gcd (int, int);
static void permute_args (int, int, int, char * const *);

static char *place = EMSG; /* option letter processing */

static int nonopt_start = -1; /* first non option argument (for permute) */
static int nonopt_end = -1;   /* first option after non options (for permute) */

/* Error messages */
static const char recargchar[] = "option requires an argument -- %c";
static const char recargstring[] = "option requires an argument -- %s";
static const char ambig[] = "ambiguous option -- %.*s";
static const char noarg[] = "option doesn't take an argument -- %.*s";
static const char illoptchar[] = "unknown option -- %c";
static const char illoptstring[] = "unknown option -- %s";


/*
 * Compute the greatest common divisor of a and b.
 */
static int
gcd(int a, int b)
{
	int c;

	c = a % b;
	while (c != 0) {
		a = b;
		b = c;
		c = a % b;
	}
	   
	return b;
}

/*
 * Exchange the block from nonopt_start to nonopt_end with the block
 * from nonopt_end to opt_end (keeping the same order of arguments
 * in each block).
 */
static void
permute_args(int panonopt_start, int panonopt_end, int opt_end,
	     char * const *nargv)
{
	int cstart, cyclelen, i, j, ncycle, nnonopts, nopts, pos;
	char *swap;

	assert(nargv != NULL);

	/*
	 * compute lengths of blocks and number and size of cycles
	 */
	nnonopts = panonopt_end - panonopt_start;
	nopts = opt_end - panonopt_end;
	ncycle = gcd(nnonopts, nopts);
	cyclelen = (opt_end - panonopt_start) / ncycle;

	for (i = 0; i < ncycle; i++) {
		cstart = panonopt_end+i;
		pos = cstart;
		for (j = 0; j < cyclelen; j++) {
			if (pos >= panonopt_end)
				pos -= nnonopts;
			else
				pos += nopts;
			swap = nargv[pos];
			/* LINTED const cast */
			((char **) nargv)[pos] = nargv[cstart];
			/* LINTED const cast */
			((char **)nargv)[cstart] = swap;
		}
	}
}

/*
 * getopt_internal --
 *	Parse argc/argv argument vector.  Called by user level routines.
 *  Returns -2 if -- is found (can be long option or end of options marker).
 */
static int
getopt_internal(int nargc, char * const *nargv, const char *options)
{
	char *oli;				/* option letter list index */
	int optchar;

	assert(nargv != NULL);
	assert(options != NULL);

	optarg = NULL;

	/*
	 * XXX Some programs (like rsyncd) expect to be able to
	 * XXX re-initialize optind to 0 and have getopt_long(3)
	 * XXX properly function again.  Work around this braindamage.
	 */
	if (optind == 0)
		optind = 1;

start:
	if (!*place) {		                /* update scanning pointer */
		if (optind >= nargc) {          /* end of argument vector */
			place = EMSG;
			if (nonopt_end != -1) {
				/* do permutation, if we have to */
				permute_args(nonopt_start, nonopt_end,
				    optind, nargv);
				optind -= nonopt_end - nonopt_start;
			}
			else if (nonopt_start != -1) {
				/*
				 * If we skipped non-options, set optind
				 * to the first of them.
				 */
				optind = nonopt_start;
			}
			nonopt_start = nonopt_end = -1;
			return -1;
		}
		if ((*(place = nargv[optind]) != '-')
		    || (place[1] == '/0')) {    /* found non-option */
			place = EMSG;
			if (IN_ORDER) {
				/*
				 * GNU extension: 
				 * return non-option as argument to option 1
				 */
				optarg = nargv[optind++];
				return INORDER;
			}
			if (!PERMUTE) {
				/*
				 * if no permutation wanted, stop parsing
				 * at first non-option
				 */
				return -1;
			}
			/* do permutation */
			if (nonopt_start == -1)
				nonopt_start = optind;
			else if (nonopt_end != -1) {
				permute_args(nonopt_start, nonopt_end,
				    optind, nargv);
				nonopt_start = optind -
				    (nonopt_end - nonopt_start);
				nonopt_end = -1;
			}
			optind++;
			/* process next argument */
			goto start;
		}
		if (nonopt_start != -1 && nonopt_end == -1)
			nonopt_end = optind;
		if (place[1] && *++place == '-') {	/* found "--" */
			place++;
			return -2;
		}
	}
	if ((optchar = (int)*place++) == (int)':' ||
	    (oli = strchr(options + (IGNORE_FIRST ? 1 : 0), optchar)) == NULL) {
		/* option letter unknown or ':' */
		if (!*place)
			++optind;
		if (PRINT_ERROR)
			fprintf(stderr, illoptchar, optchar);
		optopt = optchar;
		return BADCH;
	}
	if (optchar == 'W' && oli[1] == ';') {		/* -W long-option */
		/* XXX: what if no long options provided (called by getopt)? */
		if (*place) 
			return -2;

		if (++optind >= nargc) {	/* no arg */
			place = EMSG;
			if (PRINT_ERROR)
				fprintf(stderr, recargchar, optchar);
			optopt = optchar;
			return BADARG;
		} else				/* white space */
			place = nargv[optind];
		/*
		 * Handle -W arg the same as --arg (which causes getopt to
		 * stop parsing).
		 */
		return -2;
	}
	if (*++oli != ':') {			/* doesn't take argument */
		if (!*place)
			++optind;
	} else {				/* takes (optional) argument */
		optarg = NULL;
		if (*place)			/* no white space */
			optarg = place;
		/* XXX: disable test for :: if PC? (GNU doesn't) */
		else if (oli[1] != ':') {	/* arg not optional */
			if (++optind >= nargc) {	/* no arg */
				place = EMSG;
				if (PRINT_ERROR)
					fprintf(stderr, recargchar, optchar);
				optopt = optchar;
				return BADARG;
			} else
				optarg = nargv[optind];
		}
		place = EMSG;
		++optind;
	}
	/* dump back option letter */
	return optchar;
}

/*
 * getopt_long --
 *	Parse argc/argv argument vector.
 */
int
getopt_long(int nargc, char * const *nargv, const char *options,
	    const struct option *long_options, int *idx)
{
	int retval;

	assert(nargv != NULL);
	assert(options != NULL);
	assert(long_options != NULL);
	/* idx may be NULL */

	if ((retval = getopt_internal(nargc, nargv, options)) == -2) {
		char *current_argv, *has_equal;
		size_t current_argv_len;
		int i, match;

		current_argv = place;
		match = -1;

		optind++;
		place = EMSG;

		if (*current_argv == '/0') {		/* found "--" */
			/*
			 * We found an option (--), so if we skipped
			 * non-options, we have to permute.
			 */
			if (nonopt_end != -1) {
				permute_args(nonopt_start, nonopt_end,
				    optind, nargv);
				optind -= nonopt_end - nonopt_start;
			}
			nonopt_start = nonopt_end = -1;
			return -1;
		}
		if ((has_equal = strchr(current_argv, '=')) != NULL) {
			/* argument found (--option=arg) */
			current_argv_len = has_equal - current_argv;
			has_equal++;
		} else
			current_argv_len = strlen(current_argv);
	    
		for (i = 0; long_options[i].name; i++) {
			/* find matching long option */
			if (strncmp(current_argv, long_options[i].name,
			    current_argv_len))
				continue;

			if (strlen(long_options[i].name) ==
			    (unsigned)current_argv_len) {
				/* exact match */
				match = i;
				break;
			}
			if (match == -1)		/* partial match */
				match = i;
			else {
				/* ambiguous abbreviation */
				if (PRINT_ERROR)
					fprintf(stderr, ambig, (int)current_argv_len,
					     current_argv);
				optopt = 0;
				return BADCH;
			}
		}
		if (match != -1) {			/* option found */
		        if (long_options[match].has_arg == no_argument
			    && has_equal) {
				if (PRINT_ERROR)
					fprintf(stderr, noarg, (int)current_argv_len,
					     current_argv);
				/*
				 * XXX: GNU sets optopt to val regardless of
				 * flag
				 */
				if (long_options[match].flag == NULL)
					optopt = long_options[match].val;
				else
					optopt = 0;
				return BADARG;
			}
			if (long_options[match].has_arg == required_argument ||
			    long_options[match].has_arg == optional_argument) {
				if (has_equal)
					optarg = has_equal;
				else if (long_options[match].has_arg ==
				    required_argument) {
					/*
					 * optional argument doesn't use
					 * next nargv
					 */
					optarg = nargv[optind++];
				}
			}
			if ((long_options[match].has_arg == required_argument)
			    && (optarg == NULL)) {
				/*
				 * Missing argument; leading ':'
				 * indicates no error should be generated
				 */
				if (PRINT_ERROR)
					fprintf(stderr, recargstring, current_argv);
				/*
				 * XXX: GNU sets optopt to val regardless
				 * of flag
				 */
				if (long_options[match].flag == NULL)
					optopt = long_options[match].val;
				else
					optopt = 0;
				--optind;
				return BADARG;
			}
		} else {			/* unknown option */
			if (PRINT_ERROR)
				fprintf(stderr, illoptstring, current_argv);
			optopt = 0;
			return BADCH;
		}
		if (long_options[match].flag) {
			*long_options[match].flag = long_options[match].val;
			retval = 0;
		} else 
			retval = long_options[match].val;
		if (idx)
			*idx = match;
	}
	return retval;
}
#endif /* !GETOPT_LONG */

拿过来后，把他们放到与 destroy_linux.c 同一目录下，只需要把 destroy_linux.c 的头文件改一个地方， #include <getopt.h> 改为 #include “getopt.h” ，就能够编译运行了。而且，这样改好后，不仅在 Tru64 上能运行，在 Linux 、 SunOS 上也能运行。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "getopt.h"

void print_usage(const char *program_name) {
	printf("%s 1.0.0 (2010-06-13)/n", program_name);
	printf("This is a program decoding a BER encoded CDR file/n");
	printf("Usage: %s -f <file_name> -o <output_name> [-c <config_name>] [-k <keyword>]/n", program_name);
	printf("    -f --file       the CDR file to be decoded/n");
	printf("    -o --output     the output file in plain text format/n");
	printf("    -c --config     the description file of the CDR file, if not given, use default configuration/n");
	printf("    -k --keyword    the keyword to search, if not given, all records will be written into output file/n");
}

int main(int argc, char *argv[]) {
	char *file_name = NULL;
	char *output_name = NULL;
	char *config_name = NULL;
	char *keyword = NULL;

	const char *short_opts = "hf:o:c:k:";
	const struct option long_opts[] = {
		{"help", no_argument, NULL, 'h'},
		{"file", required_argument, NULL, 'f'},
		{"output", required_argument, NULL, 'o'},
		{"config", required_argument, NULL, 'c'},
		{"keyword", required_argument, NULL, 'k'},
		{0, 0, 0, 0}
	};
	int hflag = 0;

	int c;
	opterr = 0;

	while ( (c = getopt_long(argc, argv, short_opts, long_opts, NULL)) != -1 ) {
		switch ( c ) {
			case 'h' :
				hflag = 1;
				break;
			case 'f' :
				file_name = optarg;
				break;
			case 'o' :
				output_name = optarg;
				break;
			case 'c' :
				config_name = optarg;
				break;
			case 'k' :
				keyword = optarg;
				break;
			case '?' :
				if ( optopt == 'f' || optopt == 'o' || optopt == 'c' || optopt == 'k' )
					printf("Error: option -%c requires an argument/n", optopt);
				else if ( isprint(optopt) )
					printf("Error: unknown option '-%c'/n", optopt);
				else
					printf("Error: unknown option character '//x%x'/n", optopt);
				return 1;
			default :
				abort();
		}
	}

	if ( hflag || argc == 1 ) {
		print_usage(argv[0]);
		return 0;
	}
	if ( !file_name ) {
		printf("Error: file name must be specified/n");
		return 1;
	}
	if ( !output_name ) {
		printf("Error: output name must be specified/n");
		return 1;
	}

	// if not setting default, Linux OK, but SunOS core dump
	if ( !config_name ) config_name = "(null)";
	if ( !keyword ) keyword = "(null)";
	printf("Parameters got: file_name = %s, output_name = %s, config_name = %s, keyword = %s/n", file_name, output_name, config_name, keyword);
	return 0;
}

Linux下编译

-bash-3.2$ gcc -o destroy destroy.c getopt_long.c

短格式，全部输入

-bash-3.2$ ./destroy -f aaa -o aaa.txt -c ccc -k 222

Parameters got: file_name = aaa, output_name = aaa.txt, config_name = ccc, keyword = 222

前两个长格式，后两个短格式

-bash-3.2$ ./destroy --file aaa --output aaa.txt -c ccc -k 222

Parameters got: file_name = aaa, output_name = aaa.txt, config_name = ccc, keyword = 222

漏掉一个必须输入的参数会报错

-bash-3.2$ ./destroy -output aaa.txt

Error: file name must be specified

次序随意，长短混用

-bash-3.2$ ./destroy -c ccc -o aaa.txt -k 222 --file aaa

Parameters got: file_name = aaa, output_name = aaa.txt, config_name = ccc, keyword = 222

 

题外话，#include <filename.h>与#include “filename.h”有什么区别，是面试C程序员经常问到的一个问题。答案大家都知道了，#include <filename.h>，编译器从标准库路径搜索filename.h，而#include “filename.h”，编译器从用户的工作路径搜索filename.h。

 

此外，网上也有人说从glibc（http://sourceware.org/glibc/）上把getopt.h、getopt.c和getoptl.c拿过来也能够用。我也试过，但是不清楚什么原因不成功。

 

在这个小实验的过程中，还发现了C语言在各个OS下的一些细小差异，比如destroy.c里，79行到82行：

// if not setting default, Linux OK, but SunOS core dump

if ( !config_name ) config_name = "(null)";

if ( !keyword ) keyword = "(null)";

printf("Parameters got: file_name = %s, output_name = %s, config_name = %s, keyword = %s/n", file_name, output_name, config_name, keyword);

 

如果在81行和82行不设置空指针的默认值，Linux和Tru64都会自动帮你转换而避免运行时错误，但是SunOS不会，它会死给你看。

./destroy -f aaa -o aaa.txt

Segmentation Fault (core dumped)

 

再比如第62行的abort()在头文件stdlib.h中定义，如果不包含此文件，SunOS与Tru64编译都没问题，Linux编译时会警告：

warning: incompatible implicit declaration of built-in function abort

 

由此看来，虽然C也公认是可移植性比较好的语言，但是在跨平台的项目中，也应该注意这些微小的差别。