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 <jbasney@ncsa.uiuc.edu>
*
* 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 <jbasney@ncsa.uiuc.edu>
*
* 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。