The sequential access input procedures are procedures used on files opened for sequential access, but they can also be used on files opened for direct and keyed access.
1 – GET
The GET procedure advances the file position and reads the next
component of the file into the file buffer variable. If the
file has relative or indexed organization, the component is also
locked to prevent access by other processes.
Syntax:
GET( file_variable [[,ERROR := error-recovery]] );
The 'file_variable' is the name associated with the input file.
The 'error-recovery' specifies the action to be taken if an
error occurs during execution of the routine. By default, after
the first error, the error message is printed and execution is
stopped.
Before the GET procedure is used for the first time to read one
or more file components, the file must be in inspection mode and
prepared for reading input. Depending on the access method
specified when the file was opened, you can prepare the file for
input in the following ways:
o If the file is open for sequential access, call the RESET
procedure. RESET sets the mode to inspection, advances the
file position to the first component, and assigns the
component's value to the file buffer variable.
o If the file is open for direct access, call either the RESET
or the FIND procedure to position the file.
o If the file is open for keyed access, call the FINDK, RESET,
or RESETK procedure to position the file.
As a result of the GET procedure, the file remains in inspection
mode, and the file position advances to the next component. If
a component is found other than the end-of-file marker, the
component is locked, EOF is set to FALSE, the file buffer
variable takes on the value of the component, and UFB is set to
FALSE. If a component is not found or the end of the file is
reached, EOF and UFB are set to TRUE. If the GET procedure
fails, UFB is set to TRUE and EOF becomes undefined.
See the "HP Pascal Language Reference Manual" for the complete
description of the GET procedure.
2 – READ
The READ procedure reads one or more file components into a
variable.
Syntax:
READ( [[file_variable,]] {variable-identifier
[[:radix-specifier]]},... [[, ERROR := error-recovery]] );
The 'file_variable' is the name associated with the input file.
If you omit the name of the file, the default is INPUT.
The 'variable-identifier' is the name of the variable into which
a file component will be read; multiple identifiers are
separated by commas.
The 'radix-specifier' is one of the format values BIN, OCT, or
HEX. These values, when used on a variable identifier, will
read the variable in binary, octal, or hexadecimal radix
respectively. You can use a radix specifier only when reading
from a TEXT file.
The 'error-recovery' is the action to be taken if an error
occurs during execution of the routine. By default, after the
first error, the error message is printed and execution is
stopped.
The file must be in inspection mode before READ is called. The
file remains in inspection mode after execution of a READ
procedure.
By definition, the READ procedure for a nontext file performs an
assignment statement, a GET procedure, and an UNLOCK procedure
for each variable.
The READ procedure reads from the file until it has found a
value for each variable in the list. The first value read is
assigned to the first variable in the list, the second value
read is assigned to the second variable, and so on. The values
and the variables must be of assignment-compatible types.
Reading stops if an error occurs.
For a TEXT file, more than one component (character) can be read
into a single variable. For example, many characters can be
read into a string or converted into a numeric variable. The
READ procedure repeats the assignment, GET, and UNLOCK process
until it has read a sequence of characters that represent a
legal value for the next variable in the parameter list. The
procedure continues to read components from the file until it
has assigned a value to each variable in the list.
See the "HP Pascal Language Reference Manual" for a complete
description of the READ procedure.
3 – RESET
The RESET procedure readies a file for reading.
Syntax:
RESET( file_variable [[, file_name]]
[[, ERROR := error-recovery]] );
The 'file_variable' is the name of the file variable associated
with the input file. You do not need this argument if the file
was opened with the OPEN procedure.
The 'file_name' represents the string expression to be
associated with the 'file_variable'. If the file was previously
opened with the OPEN procedure, 'file_name' is ignored.
The 'error-recovery' represents the action to be taken if an
error occurs during execution of the routine. By default, after
the first error, the error message is printed and execution is
stopped.
The file can be in any mode before you call RESET; a call to
RESET sets the file to inspection mode. If the file is an
external file and is not already open, RESET opens it using the
same defaults as the OPEN procedure. You cannot use RESET to
create a file.
After execution of RESET, the file is positioned at the first
component, and the file buffer variable contains the value of
this component. If the file is not empty, EOF and UFB return
FALSE and the first component is locked to prevent access by
other processes. If the file is empty, EOF and UFB return TRUE.
If the file does not exist, RESET does not create it, but
returns an error at run time.
You should call RESET before reading any file with sequential
organization except the predeclared file INPUT. The RESET
procedure removes the end-of-file marker from any file connected
to a terminal device (including INPUT), thus allowing reading
from the file to continue. If you call RESET for the
predeclared file OUTPUT, an error occurs.
A call to RESET on a relative file opened for direct access
positions the file at its first existing component.
A call to RESET on an indexed file opened for keyed access
positions the file at the first component relative to the
primary key.
See the "HP Pascal Language Reference Manual" for a complete
description of the RESET procedure.