C语言 getopt_long()——正确的使用方法？

getopt_long() -- proper way to use it?

提问by Jeremy Dentel

OK, I have searched and found the following two StackOverflow topics that started me in the right direction:

好的，我已经搜索并找到了以下两个 StackOverflow 主题，它们使我朝着正确的方向前进：

Argument-parsing helpers for C/UNIX

C/UNIX 的参数解析助手

Pass arguments into C program from command line

从命令行将参数传递给 C 程序

NOTE: ALL CODE IS PSEUDO-CODE. WILL POST COMPILABLE CODE WHEN IT WORKS.

注意：所有代码都是伪代码。当它工作时将发布可编译的代码。

However, I'm still completely confused on how to use getopt_long() in C. The program I'm writing is defined as having the following possible tags (but can include as many as you absolutely need, filling the rest in with empty values):

但是，我仍然对如何在 C 中使用 getopt_long() 感到困惑。我正在编写的程序被定义为具有以下可能的标签（但可以包含您绝对需要的标签，其余的用空值填充)：

id3tagEd filename -title "title" -artist "artist" -year 1991 -comment "comment" -album "album" -track 1

Now, from what I read, I need to utilize a struct for the long options, correct? If so, I wrote something along the lines of this:

现在，从我读到的内容来看，我需要为长选项使用结构，对吗？如果是这样，我写了一些类似的东西：

struct fields field =
{
    char *[] title;
    char *[] artist;
    char *[] album;
    int year;
    char *[] comment;
    int track;
}


static struct options long_options[] =
{
    {"title", 0, &field.title, 't'},
    {"artist", 0, &field.artist, 'a'},
    {"album", 0, &field.album, 'b'},
    {"year", 0, &field.year, 'y'},
    {"comment", 0, &field.comment, 'c'},
    {"track", 0, &field.track, 'u'},
    {0, 0, 0, 0}
}

Now, from what I gathered, I would be calling it via this:

现在，根据我收集的信息，我将通过以下方式调用它：

int option_index = 0;

int values = getopt_long(argc, argv, "tabycu", long_options, &option_index);

From here, could I strictly use the field struct and do what I need to within my program? However, if this is the case, can someone explain the whole long_options struct? I read the man pages and such, and I'm just utterly confused. By rereading the man pages, I can see I can set variables to null, and should be setting all my option requirements to "required_argument"? And then setting the structs via a while() loop? However, I see optarg being used. Is this set by getopt_long()? Or is it missing from the example?

从这里开始，我可以严格使用字段结构并在我的程序中做我需要做的事情吗？但是，如果是这种情况，有人可以解释整个 long_options 结构吗？我阅读了手册页之类的内容，我完全糊涂了。通过重新阅读手册页，我可以看到我可以将变量设置为空，并且应该将所有选项要求设置为“required_argument”？然后通过 while() 循环设置结构？但是，我看到正在使用 optarg。这是由 getopt_long() 设置的吗？还是示例中缺少它？

And one last issue, I will always have an unnamed required option: filename, would I just use argv[0] to gain access to that? (Since I can assume it'll be first).

最后一个问题，我总是有一个未命名的必需选项：文件名，我是否只使用 argv[0] 来访问它？（因为我可以假设它会是第一个）。

On a side note, this is related to a homework problem, but it has nothing to do with fixing it, its more of a fundamental, have to understand argument passing and parsing in C via command line first.

附带说明一下，这与作业问题有关，但与修复它无关，它更重要的是必须首先通过命令行了解 C 中的参数传递和解析。

回答by Carl Norum

First off, you probably don't want 0for the has_argfield - it must be one of no_argument, required_arguemnt, or optional_argument. In your case, all of them are going to be required_argument. Besides that, you're not using the flagfield correctly - it has to be an integer pointer. If the corresponding flag is set, getopt_long()will fill it in with the integer you passed in via the valfield. I don't think you need this feature at all. Here's a better (shortened) example for your case:

首先，你可能不希望0的has_arg领域-它必须是一个no_argument，required_arguemnt或optional_argument。在您的情况下，所有这些都将是required_argument. 除此之外，您没有flag正确使用该字段 - 它必须是一个整数指针。如果设置了相应的标志，getopt_long()将用您通过val字段传入的整数填充它。我认为你根本不需要这个功能。这是您案例的更好（缩短）示例：

static struct option long_options[] =
{
    {"title", required_argument, NULL, 't'},
    {"artist", required_argument, NULL, 'a'},
    {NULL, 0, NULL, 0}
};

Then later, you can use it appropriately (straight from the manpage, I added some comments):

然后，您可以适当地使用它（直接从联机帮助页，我添加了一些评论）：

// loop over all of the options
while ((ch = getopt_long(argc, argv, "t:a:", long_options, NULL)) != -1)
{
    // check to see if a single character or long option came through
    switch (ch)
    {
         // short option 't'
         case 't':
             field.title = optarg; // or copy it if you want to
             break;
         // short option 'a'
         case 'a':
             field.artist = optarg; // or copy it if you want to
             break;
    }
}

You can extend for your other fields as necessary (and add some error handling, please!). Note - if you want to use -titleand -artistlike you have in your example, you'll need to use getopt_long_only(), which doesn't have short options.

您可以根据需要扩展其他字段（请添加一些错误处理！）。注意 - 如果您想在示例中使用-title并-artist像您一样使用getopt_long_only()，则需要使用，它没有简短的选项。

As to your filenameoption, you'll get that out as a '?'from the getopt_long()call, so you could handle it at that time. Your other options are to require that it is either the first or the last option and handle it by itself separately.

至于你的filename选择，你会'?'从getopt_long()电话中得到它，所以你可以在那个时候处理它。您的其他选项是要求它是第一个或最后一个选项并单独处理它。

回答by user1823890

If you use the poptlibrary, you will be able to create something smart as you did in your pseudo-code:

如果您使用popt库，您将能够像在伪代码中一样创建一些智能的东西：

#include <stdio.h>
#include "popt.h"

struct _field {
    char *title;
    char *artist;
    /* etc */
} field;

field.title = NULL;
field.artist = NULL;

/* HERE IS WHAT YOU WANTED IN YOUR PSEUDO-CODE */
struct poptOption optionsTable[] = {

   {"title", 't', POPT_ARG_STRING, &field.title, 't'
    "set the 'title' of the album" },
   {"artist", 'a', POPT_ARG_STRING, &field.artist, 'a'
    "set the 'artist' of the album" },
   POPT_AUTOHELP
   POPT_TABLEEND
};

poptContext optCon = poptGetContext(NULL, argc, argv, optionsTable, 0);
poptSetOtherOptionHelp(optCon, "[OPTIONS]");

char c;
while ((c = poptGetNextOpt(optCon)) >= 0) {
    switch (c) {
        case 't':
            /* do extra stuff only if you need */
            break;
        case 'a':
            /* do extra stuff only if you need */
            break;
        default:
            poptPrintUsage(optCon, stderr, 0);
            exit(1);
    }
}

if (field.title) printf("\nTitle is [%s]", field.title);
if (field.artist) printf("\nArtist is [%s]", field.artist)

Be smart than getopt ;)

比 getopt 聪明 ;)