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| <h4 class="subsection">16.3.3 Reading the Address of a Socket</h4> |
| |
| <p><a name="index-sys_002fsocket_002eh-1664"></a>Use the function <code>getsockname</code> to examine the address of an |
| Internet socket. The prototype for this function is in the header file |
| <samp><span class="file">sys/socket.h</span></samp>. |
| |
| <!-- sys/socket.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>getsockname</b> (<var>int socket, struct sockaddr *addr, socklen_t *length-ptr</var>)<var><a name="index-getsockname-1665"></a></var><br> |
| <blockquote><p>The <code>getsockname</code> function returns information about the |
| address of the socket <var>socket</var> in the locations specified by the |
| <var>addr</var> and <var>length-ptr</var> arguments. Note that the |
| <var>length-ptr</var> is a pointer; you should initialize it to be the |
| allocation size of <var>addr</var>, and on return it contains the actual |
| size of the address data. |
| |
| <p>The format of the address data depends on the socket namespace. The |
| length of the information is usually fixed for a given namespace, so |
| normally you can know exactly how much space is needed and can provide |
| that much. The usual practice is to allocate a place for the value |
| using the proper data type for the socket's namespace, then cast its |
| address to <code>struct sockaddr *</code> to pass it to <code>getsockname</code>. |
| |
| <p>The return value is <code>0</code> on success and <code>-1</code> on error. The |
| following <code>errno</code> error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>socket</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>ENOTSOCK</code><dd>The descriptor <var>socket</var> is not a socket. |
| |
| <br><dt><code>ENOBUFS</code><dd>There are not enough internal buffers available for the operation. |
| </dl> |
| </p></blockquote></div> |
| |
| <p>You can't read the address of a socket in the file namespace. This is |
| consistent with the rest of the system; in general, there's no way to |
| find a file's name from a descriptor for that file. |
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