Published 2023年8月10日 by

getopt_long

getopt_long可以用来解析命令行参数，也可以进行参数解析。例如

#include <stdio.h>     /* for printf */
#include <stdlib.h>    /* for exit */
#include <getopt.h>

static int verbose_flag;

int
parse(int argc, char **argv)
{
    int c;
    int digit_optind = 0;

    while (1) {
        int this_option_optind = optind ? optind : 1;
        int option_index = 0;
        static struct option long_options[] = {
            {"verbose", no_argument,       &verbose_flag, 1},
            {"add",     required_argument, 0,  0 },
            {"append",  no_argument,       0,  0 },
            {"delete",  required_argument, 0,  0 },
            {"verbose", no_argument,       0,  0 },
            {"create",  required_argument, 0, 'c'},
            {"file",    required_argument, 0,  0 },
            {0,         0,                 0,  0 }
        };

       c = getopt_long(argc, argv, "abc:d:012",
                 long_options, &option_index);
        if (c == -1)
            break;

       switch (c) {
        case 0:
            printf("option %s", long_options[option_index].name);
            if (optarg)
                printf(" with arg %s", optarg);
            printf("\n");
            break;

        case '0':
        case '1':
        case '2':
            if (digit_optind != 0 && digit_optind != this_option_optind)
              printf("digits occur in two different argv-elements.\n");
            digit_optind = this_option_optind;
            printf("option %c\n", c);
            break;

       case 'a':
            printf("option a\n");
            break;

       case 'b':
            printf("option b\n");
            break;

       case 'c':
            printf("option c with value '%s'\n", optarg);
            break;

       case 'd':
            printf("option d with value '%s'\n", optarg);
            break;

       case '?':
            break;

       default:
            printf("?? getopt returned character code 0%o ??\n", c);
        }
    }

    if (optind < argc) {
        printf("non-option ARGV-elements: ");
        while (optind < argc)
            printf("%s ", argv[optind++]);
        printf("\n");
    }

    if (verbose_flag)
        printf ("verbose flag is set\n");

    return 0;
}

void
main()
{
        char *argv[6]={0};
        int argc = 6;
        argv[0] = "prog1";
        argv[1] = "--add";
        argv[2] = "AA";
        argv[3] = "-d";
        argv[4] = "BB";
        argv[5] = "--verbose";

        parse(argc, argv);

        optind = 1;

        char *argv2[4]={0};
        int argc2 = 4;
        argv2[0] = "prog2";
        argv2[1] = "--file";
        argv2[2] = "CC";
        argv2[3] = "--verbose";
        //argv2[3] = "--delete";
        //argv2[4] = "DD";

        parse(argc2, argv2);
        return ;
}

 

getopt可以解析一个字母的命令行参数， “-d”, getopt_long则可以解析更长名称的命令行参数， 以”–“开头， 如例子中的”–file”.

参数比getopt多了两个， 函数原型如下：

#include <unistd.h>

int getopt(int argc, char * const argv[],
           const char *optstring);

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

#include <getopt.h>

int getopt_long(int argc, char * const argv[],
           const char *optstring,
           const struct option *longopts, int *longindex);

int getopt_long_only(int argc, char * const argv[],
           const char *optstring,
           const struct option *longopts, int *longindex);

 

另外注意函数依赖的定义， 编译时可以指定

getopt(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
getopt_long(), getopt_long_only(): _GNU_SOURCE

getopt_long 参数结构体相对复杂一些

struct option {
    const char *name;
    int         has_arg;
    int        *flag;
    int         val;
};



static struct option long_options[] = {
    {"verbose", no_argument,       &verbose_flag, 1},
    {"add",     required_argument, 0,  0 },
    {"append",  no_argument,       0,  0 },
    {"delete",  required_argument, 0,  0 },
    {"verbose", no_argument,       0,  0 },
    {"create",  required_argument, 0, 'c'},
    {"file",    required_argument, 0,  0 },
    {0,         0,                 0,  0 }
};

 

如果设置了flag不为null， 那么将val值复制给flag指针指向变量。

例子中是将verbose_flag设置为 1.

如果设置了flag为null， 那么val作为返回值， 这个返回值可以是设置为含义相同的短类型参数的标签，

例子中的c和create是相同的含义， 一个是长类型参数， 一个是短类型的参数。

 

另外还有个比较重要的全局变量：

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

如果 getopt() 无法识别选项字符，它将向 stderr 打印一条错误消息，将该字符存储在 optopt 中，并返回“?”。调用程序可以通过将 opterr 设置为 0 来防止出现错误消息。

因为optind存储的下一个要解析的参数， 如果是getopt_long, 可以保留optind位置， 解析出错时显示

#include <stdio.h>     /* for printf */
#include <stdlib.h>    /* for exit */
#include <getopt.h>

static int verbose_flag;

int
parse(int argc, char **argv)
{

       ...

       case '?':
            printf("unkown option  '%s'\n", argv[old_optnd]);
            break;

       default:
            printf("?? getopt returned character code 0%o ??\n", c);
        }
       old_optnd = optind;
    }
    ...
}

void
main()
{
        opterr = 0;
        char *argv[8]={0};
        int argc = 8;
        argv[0] = "prog1";
        argv[1] = "--add";
        argv[2] = "AA";
        argv[3] = "-d";
        argv[4] = "BB";
        argv[5] = "--verbose";
        argv[6] = "--error";
        argv[7] = "ddd";

        parse(argc, argv);

        optind = 1;

        char *argv2[4]={0};
        int argc2 = 4;
        argv2[0] = "prog2";
        argv2[1] = "--file";
        argv2[2] = "CC";
        argv2[3] = "--verbose";
        //argv2[3] = "--delete";
        //argv2[4] = "DD";

        parse(argc2, argv2);
        return ;
}

 

如果不设置 opterr, 会有错误输出 prog1: unrecognized option ‘–error’

garlic@garlic:~/getoption$ ./test
option add with arg AA
option d with value 'BB'
option verbose
prog1: unrecognized option '--error'
unkown option  '--error'
non-option ARGV-elements: ddd
verbose flag is set
option file with arg CC
option verbose
verbose flag is set

opterr设置为1 则没有相关输出。

解析完毕后记得要重新optind, 因为这个变量使用后不会重置。会出现 Segment Fault

 

 

参考及引用

https://www.gnu.org/software/libc/manual/html_node/Getopt-Long-Option-Example.html

https://linux.die.net/man/3/getopt_long

https://cplusplus.com/forum/unices/104742/ optind问题

图片from陳為

 

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