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| <h4 class="subsection">25.2.2 Example of Parsing Arguments with <code>getopt</code></h4> |
| |
| <p>Here is an example showing how <code>getopt</code> is typically used. The |
| key points to notice are: |
| |
| <ul> |
| <li>Normally, <code>getopt</code> is called in a loop. When <code>getopt</code> returns |
| <code>-1</code>, indicating no more options are present, the loop terminates. |
| |
| <li>A <code>switch</code> statement is used to dispatch on the return value from |
| <code>getopt</code>. In typical use, each case just sets a variable that |
| is used later in the program. |
| |
| <li>A second loop is used to process the remaining non-option arguments. |
| </ul> |
| |
| <pre class="smallexample"> #include <ctype.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <unistd.h> |
| |
| int |
| main (int argc, char **argv) |
| { |
| int aflag = 0; |
| int bflag = 0; |
| char *cvalue = NULL; |
| int index; |
| int c; |
| |
| opterr = 0; |
| |
| while ((c = getopt (argc, argv, "abc:")) != -1) |
| switch (c) |
| { |
| case 'a': |
| aflag = 1; |
| break; |
| case 'b': |
| bflag = 1; |
| break; |
| case 'c': |
| cvalue = optarg; |
| break; |
| case '?': |
| if (optopt == 'c') |
| fprintf (stderr, "Option -%c requires an argument.\n", optopt); |
| else if (isprint (optopt)) |
| fprintf (stderr, "Unknown option `-%c'.\n", optopt); |
| else |
| fprintf (stderr, |
| "Unknown option character `\\x%x'.\n", |
| optopt); |
| return 1; |
| default: |
| abort (); |
| } |
| |
| printf ("aflag = %d, bflag = %d, cvalue = %s\n", |
| aflag, bflag, cvalue); |
| |
| for (index = optind; index < argc; index++) |
| printf ("Non-option argument %s\n", argv[index]); |
| return 0; |
| } |
| </pre> |
| <p>Here are some examples showing what this program prints with different |
| combinations of arguments: |
| |
| <pre class="smallexample"> % testopt |
| aflag = 0, bflag = 0, cvalue = (null) |
| |
| % testopt -a -b |
| aflag = 1, bflag = 1, cvalue = (null) |
| |
| % testopt -ab |
| aflag = 1, bflag = 1, cvalue = (null) |
| |
| % testopt -c foo |
| aflag = 0, bflag = 0, cvalue = foo |
| |
| % testopt -cfoo |
| aflag = 0, bflag = 0, cvalue = foo |
| |
| % testopt arg1 |
| aflag = 0, bflag = 0, cvalue = (null) |
| Non-option argument arg1 |
| |
| % testopt -a arg1 |
| aflag = 1, bflag = 0, cvalue = (null) |
| Non-option argument arg1 |
| |
| % testopt -c foo arg1 |
| aflag = 0, bflag = 0, cvalue = foo |
| Non-option argument arg1 |
| |
| % testopt -a -- -b |
| aflag = 1, bflag = 0, cvalue = (null) |
| Non-option argument -b |
| |
| % testopt -a - |
| aflag = 1, bflag = 0, cvalue = (null) |
| Non-option argument - |
| </pre> |
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