对于getopt()的理解

参考书目：Linux/Unix系统编程手册 P1156

函数原型

   #include <unistd.h>

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

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

其中的argc，argv为命令行参数，optstring为需要被getopt()寻找的命令行选项合集。举例说明”:x:p::”，开头的”:”表示禁止显示错误信息（opterr被重载为0），针对未识别的选项返回’?’，针对缺少参数的选项返回’:’。x后的’:’表示选项x必须带一个参数，p后的’::’表示选项p后的参数为可选参数。
通过连续调用getopt()，可以解析命令行参数。当getopt()返回值为-1时，说明到达了选项列表的结尾。如果选项带有参数，getopt()会把全局变量optarg指向这个参数。optind指向参数列表argv中未处理的下一个元素的索引。getopt()返回-1，表示参数列表argv中解析完毕，如果此时optind小于argc，那么argv[optind]表示命令行中下一个非选项单词。

测试代码

    /*************************************************************************
    > File Name: test.c
    > Author: 0nism
    > Mail: [email protected] 
    > Created Time: Mon 03 Sep 2018 06:57:11 PM CST
     ************************************************************************/

    #include <ctype.h>
    #include "tlpi_hdr.h"

    #define printable(ch) (isprint((unsigned char) ch) ? ch : '#')

    static void usageError(char * progName, char * msg, int opt)
    {
        if (msg != NULL && opt != 0)
            fprintf(stderr, "%s (-%c)\n", msg, printable(opt));
        fprintf(stderr, "Usage: %s [-p arg] [-x]\n", progName);
        exit(EXIT_FAILURE);
    }


    int main(int argc, char * argv[])
    {
        int opt, xfnd;
        char *pstr;

        xfnd = 0;
        pstr = NULL;

        while ((opt = getopt(argc, argv, ":p:x")) != -1) 
        {   
            printf("opt =%3d (%c); optind = %d", opt, printable(opt), optind);
            if (opt == '?' || opt == ':')
                printf("; optopt =%3d (%c)", optopt, printable(optopt));
            printf("\n");

            switch (opt) {
                case 'p':   pstr = optarg;      break;
                case 'x':   xfnd++;             break;
                case ':':   usageError(argv[0], "Missing argument", optopt);
                case '?':   usageError(argv[0], "Unrecognized option", optopt);
                default:    
                    printf("Unexcepted case in switch()\n");
                    exit(EXIT_FAILURE);
            }   
        }

        if (xfnd != 0)
            printf("-x was specified (count=%d)\n", xfnd);
        if (pstr != NULL)
            printf("-p was specified with the value \"%s\"\n", pstr);
        if (optind < argc)
            printf("First nonoption argument is \"%s\", at argv[%d]\n",
                    argv[optind], optind);
        exit(EXIT_SUCCESS);
    }

测试结果

    [MISlike@iz2zeg66n0rz6nvtbg49j6z file_io]$ vim test.c
    [MISlike@iz2zeg66n0rz6nvtbg49j6z file_io]$ gcc test.c -o test      
    [MISlike@iz2zeg66n0rz6nvtbg49j6z file_io]$ ./test -x -p hello world
    opt =120 (x); optind = 2
    opt =112 (p); optind = 4
    -x was specified (count=1)
    -p was specified with the value "hello"
    First nonoption argument is "world", at argv[4]
    [MISlike@iz2zeg66n0rz6nvtbg49j6z file_io]$ ./test -p               
    opt = 58 (:); optind = 2; optopt =112 (p)
    Missing argument (-p)
    Usage: ./test [-p arg] [-x]
    [MISlike@iz2zeg66n0rz6nvtbg49j6z file_io]$ ./test -a
    opt = 63 (?); optind = 2; optopt = 97 (a)
    Unrecognized option (-a)
    Usage: ./test [-p arg] [-x]
    [MISlike@iz2zeg66n0rz6nvtbg49j6z file_io]$ ./test -p -x
    opt =112 (p); optind = 3
    -p was specified with the value "-x"