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.Dd February 5, 2022
.Dt PTSNAME 3C
.Os
.Sh NAME
.Nm ptsname
.Nd get the name of the subsidiary device of a pseudo-terminal
.Sh SYNOPSIS
.In stdlib.h
.Ft char *
.Fo ptsname
.Fa "int fildes"
.Fc
.Sh DESCRIPTION
The
.Fn ptsname
function returns the name of the pseudo-terminal subsidiary device associated
with a pseudo-terminal manager device.
The
.Fa fildes
argument is a file descriptor returned from a successful open of the
pseudo-terminal manager device; e.g., by calling
.Xr posix_openpt 3C
or by performing an
.Xr open 2
of the
.Xr ptm 4D
device.
.Pp
The
.Fn ptsname
function returns a pointer to a string containing the null-terminated
path name of the subsidiary device.
This string is of the form
.Pa /dev/pts/N ,
where
.Sy N
is a non-negative integer.
.Sh RETURN VALUES
If successful, the
.Fn ptsname
function returns a pointer to a string which is the name of the pseudo-terminal
subsidiary device.
This value points to a static data area that is overwritten by each call to
.Fn ptsname .
.Pp
Upon failure,
.Fn ptsname
returns
.Dv NULL .
This could occur if
.Fa fildes
is an invalid file descriptor or if the subsidiary device name does not exist
in the file system.
.Sh INTERFACE STABILITY
.Sy Committed
.Sh MT LEVEL
.Sy Safe
.Sh SEE ALSO
.Xr open 2 ,
.Xr grantpt 3C ,
.Xr posix_openpt 3C ,
.Xr ttyname 3C ,
.Xr unlockpt 3C ,
.Xr ptm 4D ,
.Xr pts 4D ,
.Xr attributes 7 ,
.Xr standards 7