getopt 和argc argv的联合使用

vtun如何解析启动客户端或服务器的命令行参数？

Usage:
  Server:
    vtund <-s> [-f file] [-P port] [-L local address]
  Client:
    vtund [-f file] [-p] [-m] [-t timeout] <host profile> <server address>

预备知识：

-s –f –P 等称为选项；

file port称为选项对应的参数；

host file server address ——暂且称它们为非选项字符串吧。

解析代码在main.c中。

在vtun源码中是这样实现的：

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/*每调用一次getopt返回一个选项，optarg是指向对应选项的参数指针。*/ while( (opt=getopt(argc,argv,"misf:P:L:t:npq")) != EOF ){         switch(opt)         {             case 'm':                 if (mlockall(MCL_CURRENT | MCL_FUTURE) < 0)                 {                     perror("Unable to mlockall()");                     exit(-1);                 }                 break;             case 'i':                 vtun.svr_type = VTUN_INETD;             case 's':                 svr = 1;                 break;             case 'L':                 vtun.svr_addr = strdup(optarg);                 break;             case 'P':                 vtun.bind_addr.port = atoi(optarg);                 break;             case 'f':                 vtun.cfg_file = strdup(optarg);                 break;             case 'n':                 daemon = 0;                 break;             case 'p':                 vtun.persist = 1;                 break;             case 't':                     vtun.timeout = atoi(optarg);                     break;             case 'q':                 vtun.quiet = 1;                 break;             default:                 usage();                 exit(1);         }     }//end while /*getopt不能解决非选项字符串问题，故有了下面的代码以解决非选项字符串问题*/ if(!svr)     {         /*argc-optind<2的意思是如果少于两个（或者说只有0个或1个）非选项的字符串，则退出。         *为什么？由usage我们知道client端的命令至少有两个有两个非选项字符串：         *<host profile>或<server address>.         */         if( argc - optind < 2 ){               usage();             exit(1);         }         hst = argv[optind++];    //argv[optind++]指的是第一个非选项字符串host或者server，可以理解为本次会话的名称。         if( !(host = find_host(hst)) )         {             vtun_syslog(LOG_ERR,"Host %s not found in %s", hst, vtun.cfg_file);             exit(1);         }         vtun.svr_name = strdup(argv[optind]);  //上面optind加1了，所以此处的argv[optind]指的是profile或address.     } void usage(void) {      printf("VTun ver %s\n", VTUN_VER);      printf("Usage: \n");      printf("  Server:\n");      printf("\tvtund <-s> [-f file] [-P port] [-L local address]\n");      printf("  Client:\n");      /* I don't think these work. I'm disabling the suggestion - bish 20050601*/      printf("\tvtund [-f file] " /* [-P port] [-L local address] */         "[-p] [-m] [-t timeout] <host profile> <server address>\n"); }

为充分理解getopt和argc，argv的关系，再看一个例子

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#include <unistd.h>   int main(int argc, char **argv) {     int opt;     opterr = 0;         while( (opt = getopt(argc, argv, "ab:c::d::")) != -1 )     {          switch(opt)           {               case 'a':                   printf("option=a, opt=%d, optarg=%s, optind=%d, optopt=%d\n", opt, optarg, optind, optopt);                   break;               case 'b':                   printf("option=b, opt=%d, optarg=%s, optind=%d, optopt=%d\n", opt, optarg, optind, optopt);                     break;               case 'c':                   printf("option=c, opt=%d, optarg=%s, optind=%d, optopt=%d\n", opt, optarg, optind, optopt);                      break;               case 'd':                   printf("option=d, opt=%d, optarg=%s, optind=%d, optopt=%d\n", opt, optarg, optind, optopt);                      break;               case '?':                   printf("option=?, opt=%d, optarg=%s, optind=%d, optopt=%d\n", opt, optarg, optind, optopt);                    break;                 default:                   printf("option=default, opt=%d, optarg=%s, optind=%d, optopt=%d\n", opt, optarg, optind, optopt);                      break;           }     }     printf("after getopt,optind=%d\n",optind);         //最后的optind位置是最后的有效选项或参数的下一个字符串。     printf("argc-optind=%d\n", (argc - optind));     printf("argv[optind]=%s\n", argv[optind]);     printf("argv[optind++]=%s\n", argv[optind++]);     return 0;   /* root@ubuntu:~/eclipseworkspace# ./a.out -b barg ee ff option=b, opt=98, optarg=barg, optind=3, optopt=0 after getopt,optind=3               //此时optind在ee位置 argc-optind=2 argv[optind]=ee argv[optind++]=ee */