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| <h4 class="subsection">25.2.1 Using the <code>getopt</code> function</h4> |
| |
| <p>Here are the details about how to call the <code>getopt</code> function. To |
| use this facility, your program must include the header file |
| <samp><span class="file">unistd.h</span></samp>. |
| <a name="index-unistd_002eh-3023"></a> |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| |
| <div class="defun"> |
| — Variable: int <b>opterr</b><var><a name="index-opterr-3024"></a></var><br> |
| <blockquote><p>If the value of this variable is nonzero, then <code>getopt</code> prints an |
| error message to the standard error stream if it encounters an unknown |
| option character or an option with a missing required argument. This is |
| the default behavior. If you set this variable to zero, <code>getopt</code> |
| does not print any messages, but it still returns the character <code>?</code> |
| to indicate an error. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Variable: int <b>optopt</b><var><a name="index-optopt-3025"></a></var><br> |
| <blockquote><p>When <code>getopt</code> encounters an unknown option character or an option |
| with a missing required argument, it stores that option character in |
| this variable. You can use this for providing your own diagnostic |
| messages. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Variable: int <b>optind</b><var><a name="index-optind-3026"></a></var><br> |
| <blockquote><p>This variable is set by <code>getopt</code> to the index of the next element |
| of the <var>argv</var> array to be processed. Once <code>getopt</code> has found |
| all of the option arguments, you can use this variable to determine |
| where the remaining non-option arguments begin. The initial value of |
| this variable is <code>1</code>. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Variable: char * <b>optarg</b><var><a name="index-optarg-3027"></a></var><br> |
| <blockquote><p>This variable is set by <code>getopt</code> to point at the value of the |
| option argument, for those options that accept arguments. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Function: int <b>getopt</b> (<var>int argc, char **argv, const char *options</var>)<var><a name="index-getopt-3028"></a></var><br> |
| <blockquote><p>The <code>getopt</code> function gets the next option argument from the |
| argument list specified by the <var>argv</var> and <var>argc</var> arguments. |
| Normally these values come directly from the arguments received by |
| <code>main</code>. |
| |
| <p>The <var>options</var> argument is a string that specifies the option |
| characters that are valid for this program. An option character in this |
| string can be followed by a colon (‘<samp><span class="samp">:</span></samp>’) to indicate that it takes a |
| required argument. If an option character is followed by two colons |
| (‘<samp><span class="samp">::</span></samp>’), its argument is optional; this is a GNU extension. |
| |
| <p><code>getopt</code> has three ways to deal with options that follow |
| non-options <var>argv</var> elements. The special argument ‘<samp><span class="samp">--</span></samp>’ forces |
| in all cases the end of option scanning. |
| |
| <ul> |
| <li>The default is to permute the contents of <var>argv</var> while scanning it |
| so that eventually all the non-options are at the end. This allows |
| options to be given in any order, even with programs that were not |
| written to expect this. |
| |
| <li>If the <var>options</var> argument string begins with a hyphen (‘<samp><span class="samp">-</span></samp>’), this |
| is treated specially. It permits arguments that are not options to be |
| returned as if they were associated with option character ‘<samp><span class="samp">\1</span></samp>’. |
| |
| <li>POSIX demands the following behavior: The first non-option stops option |
| processing. This mode is selected by either setting the environment |
| variable <code>POSIXLY_CORRECT</code> or beginning the <var>options</var> argument |
| string with a plus sign (‘<samp><span class="samp">+</span></samp>’). |
| </ul> |
| |
| <p>The <code>getopt</code> function returns the option character for the next |
| command line option. When no more option arguments are available, it |
| returns <code>-1</code>. There may still be more non-option arguments; you |
| must compare the external variable <code>optind</code> against the <var>argc</var> |
| parameter to check this. |
| |
| <p>If the option has an argument, <code>getopt</code> returns the argument by |
| storing it in the variable <var>optarg</var>. You don't ordinarily need to |
| copy the <code>optarg</code> string, since it is a pointer into the original |
| <var>argv</var> array, not into a static area that might be overwritten. |
| |
| <p>If <code>getopt</code> finds an option character in <var>argv</var> that was not |
| included in <var>options</var>, or a missing option argument, it returns |
| ‘<samp><span class="samp">?</span></samp>’ and sets the external variable <code>optopt</code> to the actual |
| option character. If the first character of <var>options</var> is a colon |
| (‘<samp><span class="samp">:</span></samp>’), then <code>getopt</code> returns ‘<samp><span class="samp">:</span></samp>’ instead of ‘<samp><span class="samp">?</span></samp>’ to |
| indicate a missing option argument. In addition, if the external |
| variable <code>opterr</code> is nonzero (which is the default), <code>getopt</code> |
| prints an error message. |
| </p></blockquote></div> |
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