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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <config.h>
include <fio.h>
.help nullfile
.nf ___________________________________________________________________________
NULLFILE -- Text and binary file drivers for the nullfile, "dev$null".
These special drivers behave like regular text or binary drivers but
have the special property that no i/o occurs, i.e., all output is discarded,
making it appear as if the write was successful, and EOF is returned for
all attempts to read from the file.
.endhelp ______________________________________________________________________
define MAX_NULLFILES (LAST_FD-FIRST_FD+1)
define SZ_DEFINBUF 1 # buffer size when reading
define SZ_DEFOUTBUF 2048 # buffer size when writing
define NU_INUSE 01B
define NU_READ 02B
define NU_WRITE 04B
# ZOPNNU -- Open a nullfile. Used for both binary and text nullfiles.
procedure zopnnu (osfn, mode, chan)
char osfn[ARB] # osfn version of dev$null, presumably
int mode # not used
int chan # assigned channel (output)
bool first_time
int nu
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
data first_time /true/
begin
# First time initialization.
if (first_time) {
do nu = 1, MAX_NULLFILES
flags[nu] = 0
first_time = false
}
# Find open slot.
for (nu=1; nu <= MAX_NULLFILES; nu=nu+1)
if (flags[nu] == 0)
break
if (nu > MAX_NULLFILES) {
chan = ERR
return
}
switch (mode) {
case READ_ONLY:
flags[nu] = NU_INUSE + NU_READ
case READ_WRITE:
flags[nu] = NU_INUSE + NU_READ + NU_WRITE
default:
flags[nu] = NU_INUSE + NU_WRITE
}
count[nu] = 0
chan = nu
end
# ZCLSNU -- Close a null file. Used for both text and binary null files.
procedure zclsnu (chan, status)
int chan
int status
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
if (flags[chan] == 0)
status = ERR
else {
flags[chan] = 0
status = OK
}
end
# ZSTTNU -- Status of a null file. Used for both text and binary null files.
procedure zsttnu (chan, param, lvalue)
int chan
int param
long lvalue
int and()
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
switch (param) {
case FSTT_BLKSIZE:
lvalue = 0
case FSTT_FILSIZE:
lvalue = 0
case FSTT_OPTBUFSIZE, FSTT_MAXBUFSIZE:
if (and (flags[chan], NU_WRITE) != 0)
lvalue = SZ_DEFOUTBUF
else
lvalue = SZ_DEFINBUF
}
end
# ZARDNU, ZAWRNU, ZAWTNU -- Binary file i/o to the null file.
procedure zardnu (chan, buf, maxbytes, loffset)
int chan, maxbytes
char buf[ARB]
long loffset
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
count[chan] = 0
end
procedure zawrnu (chan, buf, nbytes, loffset)
int chan, nbytes
char buf[ARB]
long loffset
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
count[chan] = nbytes
end
procedure zawtnu (chan, status)
int chan, status
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
if (flags[chan] != 0)
status = count[chan]
else
status = ERR
end
# ZGETNU, ZPUTNU, ZFLSNU, ZSEKNU, ZNOTNU -- Text file i/o to the null file.
procedure zgetnu (chan, buf, maxch, status)
int chan, maxch, status
char buf[ARB]
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
if (flags[chan] != 0)
status = 0
else
status = ERR
end
procedure zputnu (chan, buf, nchars, status)
int chan, nchars, status
char buf[ARB]
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
if (flags[chan] != 0)
status = nchars
else
status = ERR
end
procedure zflsnu (chan, status)
int chan
int status
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
if (flags[chan] != 0)
status = OK
else
status = ERR
end
procedure zseknu (chan, loffset, status)
int chan, status
long loffset
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
if (flags[chan] != 0)
status = OK
else
status = ERR
end
procedure znotnu (chan, loffset)
int chan
long loffset
int flags[MAX_NULLFILES]
int count[MAX_NULLFILES]
common /znucom/ flags, count
begin
if (flags[chan] != 0)
loffset = 0
else
loffset = ERR
end
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