getopt不解析参数的可选参数

Question

在C中,getopt_long不会解析命令行参数参数的可选参数.

当我运行程序时,无法识别可选参数,如下面的示例运行.

$ ./respond --praise John
Kudos to John
$ ./respond --blame John
You suck !
$ ./respond --blame
You suck !

这是测试代码.

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

int main(int argc, char ** argv )
{
    int getopt_ret, option_index;
    static struct option long_options[] = {
               {"praise",  required_argument, 0, 'p'},
               {"blame",  optional_argument, 0, 'b'},
               {0, 0, 0, 0}       };
    while (1) {
        getopt_ret = getopt_long( argc, argv, "p:b::",
                                  long_options,  &option_index);
        if (getopt_ret == -1) break;

        switch(getopt_ret)
        {
            case 0: break;
            case 'p':
                printf("Kudos to %s\n", optarg); break;
            case 'b':
                printf("You suck ");
                if (optarg)
                    printf (", %s!\n", optarg);
                else
                    printf ("!\n", optarg);
                break;
            case '?':
                printf("Unknown option\n"); break;
        }
    } 
    return 0;
}

Answer 1

虽然在glibc文档或getopt手册页中没有提到,但长样式命令行参数的可选参数需要'等号'(=).将可选参数与参数分隔开的空格不起作用.

使用测试代码运行的示例:

$ ./respond --praise John
Kudos to John
$ ./respond --praise=John
Kudos to John
$ ./respond --blame John
You suck !
$ ./respond --blame=John
You suck , John!

Answer 2

手册页肯定没有很好地记录,但源代码有点帮助.

简单地说:你应该做类似以下的事情(虽然这可能有点过于迂腐):

if(   !optarg
   && optind < argc // make sure optind is valid
   && NULL != argv[optind] // make sure it's not a null string
   && '\0' != argv[optind][0] // ... or an empty string
   && '-' != argv[optind][0] // ... or another option
  ) {
  // update optind so the next getopt_long invocation skips argv[optind]
  my_optarg = argv[optind++];
}
/* ... */

从_getopt_internal之前的注释中:

...

如果getopt找到另一个选项字符,它将返回该字符,进行 更新optind,nextchar以便下一次调用getopt可以使用以下选项字符或ARGV-element恢复扫描.

如果没有其他选项字符,则getopt返回-1.然后optind是ARGV中第一个ARGV元素的索引,它不是一个选项.(ARGV元素已经被置换,因此那些不是选项的元素现在已经存在了.)<-- a note from me: if the 3rd argument to getopt_long starts with a dash, argv will not be permuted

...

如果OPTSTRING中的char后跟冒号,则意味着它需要一个arg,因此返回同一ARGV元素中的以下文本或下一个ARGV元素的文本optarg.两个冒号意味着需要一个可选的arg的选项; 如果当前ARGV元素中有文本,则返回optarg,否则optarg设置为零.

...

......虽然你必须在两行之间做一些阅读.以下是您想要的:

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

int main(int argc, char* argv[] ) {
  int getopt_ret;
  int option_index;
  static struct option long_options[] = {
      {"praise",  required_argument, 0, 'p'}
    , {"blame",  optional_argument, 0, 'b'}
    , {0, 0, 0, 0}
  };

  while( -1 != ( getopt_ret = getopt_long(  argc
                                          , argv
                                          , "p:b::"
                                          , long_options
                                          , &option_index) ) ) {
    const char *tmp_optarg = optarg;
    switch( getopt_ret ) {
      case 0: break;
      case 1:
        // handle non-option arguments here if you put a `-`
        // at the beginning of getopt_long's 3rd argument
        break;
      case 'p':
        printf("Kudos to %s\n", optarg); break;
      case 'b':
        if(   !optarg
           && NULL != argv[optindex]
           && '-' != argv[optindex][0] ) {
          // This is what makes it work; if `optarg` isn't set
          // and argv[optindex] doesn't look like another option,
          // then assume it's our parameter and overtly modify optindex
          // to compensate.
          //
          // I'm not terribly fond of how this is done in the getopt
          // API, but if you look at the man page it documents the
          // existence of `optarg`, `optindex`, etc, and they're
          // not marked const -- implying they expect and intend you
          // to modify them if needed.
          tmp_optarg = argv[optindex++];
        }
        printf( "You suck" );
        if (tmp_optarg) {
          printf (", %s!\n", tmp_optarg);
        } else {
          printf ("!\n");
        }
        break;
      case '?':
        printf("Unknown option\n");
        break;
      default:
        printf( "Unknown: getopt_ret == %d\n", getopt_ret );
        break;
    }
  }
  return 0;
}