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| <h4 class="subsection">17.8.1 Allocating Pseudo-Terminals</h4> |
| |
| <p><a name="index-allocating-pseudo_002dterminals-2024"></a> |
| <a name="index-stdlib_002eh-2025"></a>This subsection describes functions for allocating a pseudo-terminal, |
| and for making this pseudo-terminal available for actual use. These |
| functions are declared in the header file <samp><span class="file">stdlib.h</span></samp>. |
| |
| <!-- stdlib.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: int <b>getpt</b> (<var>void</var>)<var><a name="index-getpt-2026"></a></var><br> |
| <blockquote><p>The <code>getpt</code> function returns a new file descriptor for the next |
| available master pseudo-terminal. The normal return value from |
| <code>getpt</code> is a non-negative integer file descriptor. In the case of |
| an error, a value of -1 is returned instead. The following |
| <code>errno</code> conditions are defined for this function: |
| |
| <dl> |
| <dt><code>ENOENT</code><dd>There are no free master pseudo-terminals available. |
| </dl> |
| |
| <p>This function is a GNU extension. |
| </p></blockquote></div> |
| |
| <!-- stdlib.h --> |
| <!-- SVID, XPG4.2 --> |
| <div class="defun"> |
| — Function: int <b>grantpt</b> (<var>int filedes</var>)<var><a name="index-grantpt-2027"></a></var><br> |
| <blockquote><p>The <code>grantpt</code> function changes the ownership and access permission |
| of the slave pseudo-terminal device corresponding to the master |
| pseudo-terminal device associated with the file descriptor |
| <var>filedes</var>. The owner is set from the real user ID of the calling |
| process (see <a href="Process-Persona.html#Process-Persona">Process Persona</a>), and the group is set to a special |
| group (typically <dfn>tty</dfn>) or from the real group ID of the calling |
| process. The access permission is set such that the file is both |
| readable and writable by the owner and only writable by the group. |
| |
| <p>On some systems this function is implemented by invoking a special |
| <code>setuid</code> root program (see <a href="How-Change-Persona.html#How-Change-Persona">How Change Persona</a>). As a |
| consequence, installing a signal handler for the <code>SIGCHLD</code> signal |
| (see <a href="Job-Control-Signals.html#Job-Control-Signals">Job Control Signals</a>) may interfere with a call to |
| <code>grantpt</code>. |
| |
| <p>The normal return value from <code>grantpt</code> is 0; a value of |
| -1 is returned in case of failure. The following <code>errno</code> |
| error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>EINVAL</code><dd>The <var>filedes</var> argument is not associated with a master pseudo-terminal |
| device. |
| |
| <br><dt><code>EACCES</code><dd>The slave pseudo-terminal device corresponding to the master associated |
| with <var>filedes</var> could not be accessed. |
| </dl> |
| |
| </blockquote></div> |
| |
| <!-- stdlib.h --> |
| <!-- SVID, XPG4.2 --> |
| <div class="defun"> |
| — Function: int <b>unlockpt</b> (<var>int filedes</var>)<var><a name="index-unlockpt-2028"></a></var><br> |
| <blockquote><p>The <code>unlockpt</code> function unlocks the slave pseudo-terminal device |
| corresponding to the master pseudo-terminal device associated with the |
| file descriptor <var>filedes</var>. On many systems, the slave can only be |
| opened after unlocking, so portable applications should always call |
| <code>unlockpt</code> before trying to open the slave. |
| |
| <p>The normal return value from <code>unlockpt</code> is 0; a value of |
| -1 is returned in case of failure. The following <code>errno</code> |
| error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>EINVAL</code><dd>The <var>filedes</var> argument is not associated with a master pseudo-terminal |
| device. |
| </dl> |
| </p></blockquote></div> |
| |
| <!-- stdlib.h --> |
| <!-- SVID, XPG4.2 --> |
| <div class="defun"> |
| — Function: char * <b>ptsname</b> (<var>int filedes</var>)<var><a name="index-ptsname-2029"></a></var><br> |
| <blockquote><p>If the file descriptor <var>filedes</var> is associated with a |
| master pseudo-terminal device, the <code>ptsname</code> function returns a |
| pointer to a statically-allocated, null-terminated string containing the |
| file name of the associated slave pseudo-terminal file. This string |
| might be overwritten by subsequent calls to <code>ptsname</code>. |
| </p></blockquote></div> |
| |
| <!-- stdlib.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: int <b>ptsname_r</b> (<var>int filedes, char *buf, size_t len</var>)<var><a name="index-ptsname_005fr-2030"></a></var><br> |
| <blockquote><p>The <code>ptsname_r</code> function is similar to the <code>ptsname</code> function |
| except that it places its result into the user-specified buffer starting |
| at <var>buf</var> with length <var>len</var>. |
| |
| <p>This function is a GNU extension. |
| </p></blockquote></div> |
| |
| <p><strong>Portability Note:</strong> On System V<!-- /@w --> derived systems, the file |
| returned by the <code>ptsname</code> and <code>ptsname_r</code> functions may be |
| STREAMS-based, and therefore require additional processing after opening |
| before it actually behaves as a pseudo terminal. |
| <!-- FIXME: xref STREAMS --> |
| |
| <p>Typical usage of these functions is illustrated by the following example: |
| <pre class="smallexample"> int |
| open_pty_pair (int *amaster, int *aslave) |
| { |
| int master, slave; |
| char *name; |
| |
| master = getpt (); |
| if (master < 0) |
| return 0; |
| |
| if (grantpt (master) < 0 || unlockpt (master) < 0) |
| goto close_master; |
| name = ptsname (master); |
| if (name == NULL) |
| goto close_master; |
| |
| slave = open (name, O_RDWR); |
| if (slave == -1) |
| goto close_master; |
| |
| if (isastream (slave)) |
| { |
| if (ioctl (slave, I_PUSH, "ptem") < 0 |
| || ioctl (slave, I_PUSH, "ldterm") < 0) |
| goto close_slave; |
| } |
| |
| *amaster = master; |
| *aslave = slave; |
| return 1; |
| |
| close_slave: |
| close (slave); |
| |
| close_master: |
| close (master); |
| return 0; |
| } |
| </pre> |
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