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Dieses Gerät hat auch andere Anweisungen:
Anleitung Zusammenfassung
USING
CKREWRITE
In
order
to
call
pro cedure
CKREWRITE,
the
le
m
ust
b e
op en
for
b oth
input
and
output
(inputoutput
t
yp e=2).
The
access
mo
de
can
b e
sequen
tial,
random,
or
dynamic.
If
access
mo
de
is
sequen
tial,
CKREAD
m
ust
ha
v
e
b een
executed
successfully
just
prior
to
the
call
to
CKREWRITE.
In
random
or
dynamic
mo
de,
no
prior
read
is
required;
the
system
searc
hes
the
le
for
the
record
to
b e
rewritten.
REWRITE
IN
SEQUENTIAL
MODE.
When
the
le
is
op ened
in
sequen
tial
mo
de
(access
mo
de
=
0),
CKREAD
m
ust
b e
executed
b efore
CKREWRITE,
The
primary
k
ey
in
the
record
to
b e
written
b
y
CKREWRITE
m
ust
b e
iden
tical
to
the
primary
k
ey
in
the
record
read
b
y
CKREAD.
A
simple
w
a
y
to
insure
that
the
k
eys
match
is
to
read
a
record
in
to
W
ORKING-STORA
GE,
mo
dify
it
without
altering
the
primary
k
ey
,
and
then
write
it
bac
k
to
the
le
using
CKREWRITE.
Since
the
primary
k
ey
is
not
c
hanged,
the
sequence
of
records
in
the
le
is
not
aected.
Rewriting
Records
With
Duplicate
Keys .
If
y
ou
w
an
t
to
rewrite
in
sequen
tial
mo
de
all
the
records
in
a
c
hain
of
records
with
duplicate
k
eys,
use
either
CKST
AR
T
or
CKREADBYKEY
to
p osition
to
the
rst
record
in
the
c
hain.
Then
call
CKREWRITE
to
up date
the
rst
record
in
the
c
hain.
Subsequen
t
calls
dep end
on
whether
y
ou
are
c
hanging
an
y
k
ey
v
alue
in
the
record
(not
necessarily
the
selected
k
ey).
If
no
k
ey
in
the
record
is
c
hanged,
the
record
p ointer
con
tinues
to
p oint
to
the
curren
t
record.
Only
a
subsequen
t
CKREAD
adv
ances
the
p ointer
to
the
next
record
in
the
duplicate
k
ey
c
hain.
In
this
case,
y
ou
can
issue
CKREAD
and
CKREWRITE
calls
un
til
all
records
with
the
duplicated
k
ey
v
alue
ha
v
e
b een
rewritten.
If
an
y
k
ey
in
the
record
is
c
hanged,
the
new
k
ey
is
written
to
the
end
of
the
c
hain
of
duplicate
k
eys
in
the
k
ey
le.
After
the
rst
call
to
CKREWRITE,
the
record
p ointer
p oints
to
the
record
whose
k
ey
v
alue
follows
the
c
hanged
k
ey
.
Since
this
k
ey
is
no
w
at
the
end
of
the
c
hain
of
duplicate
k
eys,
a
subsequen
t
call
to
CKREWRITE
skips
all
records
with
k
eys
in
the
duplicate
k
ey
c
hain
and
rewrites
the
record
with
the
next
higher
k
ey
v
alue.
In
this
case,
y
ou
m
ust
precede
eac
h
call
to
CKREWRITE
with
a
call
to
CKST
AR
T
or
CKREADBYKEY
in
order
to
up date
all
subsequen
t
records
with
duplicate
k
eys.
If
y
ou
are
up dating
a
primary
k
ey
v
alue
whic
h
is
duplicated,
it
is
go
o d
practice
to
use
CKDELETE
to
delete
the
selected
record
and
then
rewrite
it
as
a
new
record
with
CKWRITE.
REWRITE
IN
RANDOM
MODE.
When
the
le
is
op ened
in
random
or
dynamic
mo
de
(access
mo
de
=
1
or
2),
no
prior
call
to
a
read
pro cedure
is
needed.
Y
ou
sp ecify
the
record
to
b e
written
in
W
ORKING-STORA
GE
and
then
call
CKREWRITE.
Ho
w
ev
er,
y
ou
m
ust
use
the
primary
k
ey
to
p osition
to
the
record
to
b e
mo
died.
When
the
pro cedure
is
executed,
the
le
is
searc
hed
for
a
record
whose
primary
k
ey
matches
that
of
the
record
to
b e
written.
If
suc
h
a
record
is
found,
it
is
replaced
b
y
the
record
sp ecied
in
CKREWRITE.
If
not
found,
an
in
v
alid
k
ey
condition
is
diagnosed
and
status
is
set
to
the
\23".
A
call
to
CKREWRITE
in
random
mo
de
only
up dates
the
rst
record
with
a
k
ey
in
the
c
hain
of
duplicate
k
eys.
POSITION
OF
POINTER .
Regardless
of
the
mo
de,
after
an
y
call
to
CKREWRITE
that
do es
not
mo
dify
a
k
ey
v
alue,
the
record
p ointer
is
p ositioned
to
the
k
ey
of
the
record
just
mo
died.
Ho
w
ev
er,
if
an
y
k
ey
in
the
mo
died
record
w
as
c
hanged,
the
record
m
ust
b e
deleted
and
then
rewritten
b
y
a
write
pro cedure.
If
the
access
mo
de
is
sequen
tial
and
a
k
ey
w
as
mo
died,
the
p ointer
is
mov
ed
to
the
record
with
the
next
k
ey
v
alue
in
ascending
sequence
after
the
3-28
USING
KSAM
FILES
IN
COBOL
PROGRAMS
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