在C中使用getopt（）和switch语句

Question

I'm new to C and trying to use getopt combined with a switch statement. I think my problem is just a syntax one but I can't seem to figure it out. I need to run my program like this : $/webserver -p 8080 -r /my/root/dir . So I need to recognize the -p and get the 8080 and the recognize the -r and get the /my/root/dir. Currently my code finds the -p and then finds the -r and then detects an unknown option and exits. Here is the code. I have the puts() in there for testing.

   #define USAGE_STRING "Usage: webserver -p <port> -r  <rootdir>\n"
char *port;
char *rootdir;
// Process command line arguments. Uses GNU getopt() function.
void processargs(int argc, char **argv) {
  int next_option;
  do {
    next_option = getopt(argc, argv, "pr:");
    if (next_option != -1) {
      switch (next_option)
      {
        case 'p': /* -p -- port option  */
          puts("p");

          port = optarg;
         printf("%s", port);
        case 'r': // -r -- root directory option
          puts("r");
          rootdir = optarg;  
        printf("%s", rootdir);
        default:
             puts("unknown");
          /* Unknown option detected. Print it to standard
                output, and exit with exit code zero (normal termination). */
          fprintf(stderr, USAGE_STRING);
          exit(1);

      }
    }
  } while (next_option != -1);
  printf("%s", port);

  if (port == NULL) {

          fprintf(stderr, USAGE_STRING);
          exit(1);
    }
  if (rootdir == NULL) {
  puts("unknown");
          fprintf(stderr, USAGE_STRING);
          exit(1);
    }


}

Currently when I run the above command I get this output (using the puts for testing).

p
r
unknown
Usage: webserver -p <port> -r  <rootdir>

Thanks for any help!

Answer 1

我相信您希望在每种情况下都使用break ，否则执行将进入下一个case块。

Answer 2

AC switch statement requires a break at the end of each case, otherwise the code in the following case is executed. So this:

switch (next_option)
{
case 'p':                      /* -p -- port option */
    puts("p");

    port = optarg;
    printf("%s", port);
case 'r':                      // -r -- root directory option
    puts("r");
    rootdir = optarg;
    printf("%s", rootdir);
default:
    puts("unknown");
    /* Unknown option detected. Print it to standard output, and exit with exit code zero
       (normal termination). */
    fprintf(stderr, USAGE_STRING);
    exit(1);
}

Must be changed to this:

switch (next_option)
{
case 'p':                      /* -p -- port option */
    puts("p");

    port = optarg;
    printf("%s", port);
    break;
case 'r':                      // -r -- root directory option
    puts("r");
    rootdir = optarg;
    printf("%s", rootdir);
    break;
default:
    puts("unknown");
    /* Unknown option detected. Print it to standard output, and exit with exit code zero
       (normal termination). */
    fprintf(stderr, USAGE_STRING);
    exit(1);
}

Answer 3

First you should be using getopt_long() I believe getopt() is depreciated. You are also missing break in your switch statement. With out break each case beneath that one will be executed. While you could use a do-while loop it's simpler to just use a while loop.

Here's a simple command line parser you can build on.

static const char *optstring = "p:r:";

static struct option longopts[] =
{
    { "port", required_argument, NULL, 'p' },
    { "root", required_argument, NULL, 'r' },
    { NULL, 0, NULL, 0 }
};

int parseInput(int argc, char * const argv[])
{
    int ch;

    /* Main Loop ie the Parser */
    while ((ch = getopt_long(argc, argv, optstring, longopts, NULL)) != -1)
    {
        switch(ch)
        {
            case 'p':
                printf("arg: %s\n", optarg);
                break;

            case 'r':
                printf("arg: %s\n", optarg);
                break;

            default:
                printf("Unsupported option\n");
                return -1;
        }
   }
   return 0;
}