Purpose
The READ statement is the data transfer input statement.
Syntax
>>-READ--+-name---------------------------------------+--------><
+-format--+--------------------+-------------+
| '-,--input_item_list-' |
'-(--io_control_list--)--+-----------------+-'
'-input_item_list-'
|
- format
- is a format identifier, described below under
FMT=format. In addition, it cannot be a Hollerith
constant.
- name
- is a namelist group name
- input_item
- is an input list item. An input list specifies the data to be
transferred. An input list item can be:
- A variable name, but not for an assumed-size array. An array is
treated as if all of its elements were specified in the order they are
arranged in storage.
A pointer must be associated with a definable target, and an allocatable
object must be allocated. A derived-type object cannot have any
ultimate component that is outside the scoping unit of this statement.
The evaluation of input_item cannot result in a derived-type object
that contains a pointer. The structure components of a structure in a
formatted statement are treated as if they appear in the order of the
derived-type definition; in an unformatted statement, the structure
components are treated as a single value in their internal representation
(including padding).
- An implied-DO list, as described under Implied-DO List.
- io_control
- is a list that must contain one unit specifier (UNIT=) and can
also contain one of each of the other valid specifiers described below.
- [UNIT=] u
- is a unit specifier that specifies the unit to be used in the input
operation. u is an external unit identifier or internal file
identifier.
+-------------------------------IBM Extension--------------------------------+
An external unit identifier refers to an external file. It is one of
the following:
- An integer expression whose value is in the range 0 through
2,147,483,647.
- An asterisk, which identifies external unit 5 and is preconnected to
standard input.
+----------------------------End of IBM Extension----------------------------+
An internal file identifier refers to an internal file. It is the
name of a character variable that cannot be an array section with a vector
subscript.
If the optional characters UNIT= are omitted, u must be
the first item in io_control_list. If the optional characters
UNIT= are specified, either the optional characters FMT= or
the optional characters NML= must also be present.
- [FMT=] format
- is a format specifier that specifies the format to be used in the input
operation. format is a format identifier that can be:
- The statement label of a FORMAT statement. The
FORMAT statement must be in the same scoping unit.
- The name of a scalar INTEGER(4) or INTEGER(8) variable
that was assigned the statement label of a FORMAT statement.
The FORMAT statement must be in the same scoping unit.
+---------------------------------Fortran 95---------------------------------+
Fortran 95 does not permit assigning of a statement
label.
+-----------------------------End of Fortran 95------------------------------+
- A character constant. It must begin with a left parenthesis and end
with a right parenthesis. Only the format codes described in the
FORMAT statement can be used between the parentheses. Blank
characters can precede the left parenthesis, or follow the right
parenthesis.
- A character variable that contains character data whose leftmost character
positions constitute a valid format. A valid format begins with a left
parenthesis and ends with a right parenthesis. Only the format codes
listed under FORMAT can be used between the parentheses. Blank characters
can precede the left parenthesis or follow the right parenthesis. If
format is an array element, the format identifier must not exceed the
length of the array element.
- An array of noncharacter intrinsic type. The data must be a valid
format identifier as described under character array.
- Any character expression, except one involving concatenation of an operand
that specifies inherited length, unless the operand is the name of a
constant.
- An asterisk, specifying list-directed formatting.
- A namelist specifier that specifies the name of a
namelist list that you have previously defined.
If the optional characters FMT= are omitted, format must
be the second item in io_control_list and the first item must be the
unit specifier with the optional characters UNIT= omitted.
Both NML= and FMT= cannot be specified in the same input
statement.
- ADVANCE= char_expr
- is an advance specifier that determines whether nonadvancing input occurs
for this statement. char_expr is a scalar character expression
that must evaluate to YES or NO. If NO is
specified, nonadvancing input occurs. If YES is specified,
advancing, formatted sequential or stream input occurs. The default
value is YES. ADVANCE= can be specified only in a
formatted sequential or formatted stream READ statement with an
explicit format specification that does not specify an internal file unit
specifier.
- END= stmt_label
- is an end-of-file specifier that specifies a statement label at which the
program is to continue if an endfile record is encountered and no error
occurs. An external file is positioned after the endfile record;
the IOSTAT= specifier, if present, is assigned a negative value;
and the NUM= specifier, if present, is assigned an integer
value. If an error occurs and the statement contains the SIZE=
specifier, the specified variable becomes defined with an integer
value. Coding the END= specifier suppresses the error message
for end-of-file. This specifier can be specified for a unit connected
for either sequential or direct access.
- EOR= stmt_label
- is an end-of-record specifier. If the specifier is present, an
end-of-record condition occurs, and no error condition occurs during execution
of the statement. If PAD= exists, the following also
occur:
- If the PAD= specifier has the value YES, the record is
padded with blanks to satisfy the input list item and the corresponding data
edit descriptor that requires more characters than the record contains.
- Execution of the READ statement terminates.
- The file specified in the READ statement is positioned after the
current record.
- If the IOSTAT= specifier is present, the specified variable
becomes defined with a negative value different from an end-of-file
value.
- If the SIZE= specifier is present, the specified variable becomes
defined with an integer value.
- Execution continues with the statement containing the statement label
specified by the EOR= specifier.
- End-of-record messages are suppressed.
- ERR= stmt_label
- is an error specifier that specifies the statement label of an executable
statement to which control is to transfer in the case of an error.
Coding the ERR= specifier suppresses error
messages.
+-------------------------------IBM Extension--------------------------------+
- ID= integer_variable
- indicates that the data transfer is to be done
asynchronously. The integer_variable is an integer
variable. If no error is encountered, the integer_variable is defined
with a value after executing the asynchronous data transfer statement.
This value must be used in the matching WAIT statement.
Asynchronous data transfer must either be direct unformatted,
sequential unformatted or stream unformatted. Asynchronous I/O to
internal files is prohibited. Asynchronous I/O to raw character devices
(for example, to tapes or raw logical volumes) is prohibited. The
integer_variable must not be associated with any entity in the data
transfer I/O list, or with a do_variable of an io_implied_do
in the data transfer I/O list. If the integer_variable is an
array element reference, its subscript values must not be affected by the data
transfer, the io_implied_do processing, or the definition or
evaluation of any other specifier in the io_control_spec.
+----------------------------End of IBM Extension----------------------------+
- IOMSG= iomsg_variable
- is an input/output status specifier that specifies the message returned by
the input/output operation. iomsg_variable is a scalar default
character variable. It must not be a use-associated nonpointer
protected variable. When the input/output statement containing this
specifier finishes execution, iomsg_variable is defined as
follows:
- If an error, end-of-file, or end-of-record condition occurs, the variable
is assigned an explanatory message as if by assignment.
- If no such condition occurs, the value of the variable is
unchanged.
- IOSTAT= ios
- is an input/output status specifier that specifies the status of the
input/output operation. ios is an integer variable.
Coding the IOSTAT= specifier suppresses error messages. When
the statement finishes execution, ios is defined with:
- A zero value if no error condition, end-of-file condition, or
end-of-record condition occurs.
- A positive value if an error occurs.
- A negative value if an end-of-file condition is encountered and no error
occurs.
- A negative value that is different from the end-of-file value if an
end-of-record condition occurs and no error condition or end-of-file condition
occurs.
- [NML=] name
- is a namelist specifier that specifies the name
of a namelist list that you have previously defined. If the optional
characters NML=are not specified, the namelist name must appear as
the second parameter in the list and the first item must be the unit specifier
with UNIT= omitted. If both NML=and UNIT=are
specified, all the parameters can appear in any order. The
NML= specifier is an alternative to FMT=; both
NML= and FMT= cannot be specified in the same input
statement.
+-------------------------------IBM Extension--------------------------------+
- NUM= integer_variable
- is a number specifier that specifies the number of bytes of data
transmitted between the I/O list and the file. integer_variable is an integer variable. The NUM= specifier is only permitted for unformatted
output. Coding the NUM parameter suppresses the indication of
an error that would occur if the number of bytes represented by the output
list is greater than the number of bytes that can be written into the
record. In this case, integer_variable is set to a value that
is the maximum length record that can be written. Data from remaining
output list items is not written into subsequent records.
+----------------------------End of IBM Extension----------------------------+
- POS=integer_expr
-
integer_expr is an integer expression greater than
0. POS= specifies the file position of the file storage unit
to be read in a file connected for stream access. You must not use
POS= for a file that cannot be positioned.
- REC= integer_expr
- is a record specifier that specifies the number of the record to be read
in a file connected for direct access. The REC= specifier is
only permitted for direct input. integer_expr is an integer
expression whose value is positive. A record specifier is not valid if
list-directed or namelist formatting is used and if the unit specifier
specifies an internal file. The END= specifier can appear concurrently. The record specifier represents the relative position of a record
within a file. The relative position number of the first record is
1. You must not specify REC= in data transfer statements that
specify a unit connected for stream access, or use the POS=
specifier.
- SIZE= count
- is a character count specifier that determines how many characters
are transferred by data edit descriptors during execution of the current input
statement. count is an integer variable. Blanks that
are inserted as padding are not included in the count.
>>-(--do_object_list-- , --------------------------------------->
>--do_variable = arith_expr1, arith_expr2----------------------->
>--+---+--+-------------+--)-----------------------------------><
'-,-' '-arith_expr3-'
|
- do_object
- is an output list item
- do_variable
- is a named scalar variable of type integer or real
- arith_expr1, arith_expr2, and
arith_expr3
- are scalar numeric expressions
The range of an implied-DO list is the list
do_object_list. The iteration count and the values of the
DO variable are established from arith_expr1,
arith_expr2, and arith_expr3, the same as for a DO
statement. When the implied-DO list is executed, the items in
the do_object_list are specified once for each iteration of the
implied-DO list, with the appropriate substitution of values for any
occurrence of the DO variable.
The DO variable or an associated data item must not appear as an
input list item in the do_object_list, but can be read in the same
READ statement outside of the implied-DO list.
Rules
Any statement label specified by the ERR=, EOR= and
END= specifiers must refer to a branch target statement that appears
in the same scoping unit as the READ statement.
If either the EOR= specifier or the SIZE= specifier is
present, the ADVANCE= specifier must also be present and must have
the value NO.
+-------------------------------IBM Extension--------------------------------+
If a NUM= specifier is present, neither a format specifier
nor a namelist specifier can be present.
+----------------------------End of IBM Extension----------------------------+
Variables specified for the IOSTAT=, SIZE= and
NUM= specifiers must not be associated with any input list item,
namelist list item, or the DO variable of an implied-DO
list. If such a specifier variable is an array element, its subscript
values must not be affected by the data transfer, any implied-DO
processing, or the definition or evaluation of any other specifier.
A READ statement without io_control_list specified
specifies the same unit as a READ statement with
io_control_list specified in which the external unit identifier is an
asterisk.
If the ERR= and IOSTAT= specifiers are set and an error
is encountered during a synchronous data transfer, transfer is made to the
statement specified by the ERR= specifier and a positive integer
value is assigned to ios.
+-------------------------------IBM Extension--------------------------------+
If the ERR= or IOSTAT= specifiers
are set and an error is encountered during an asynchronous data transfer,
execution of the matching WAIT statement is not required.
If the END= or IOSTAT= specifiers are set and an
end-of-file condition is encountered during an asynchronous data transfer,
execution of the matching WAIT statement is not required.
If a conversion error is encountered and the CNVERR run-time
option is set to NO, ERR= is not branched to, although
IOSTAT= may be set.
If IOSTAT= and ERR= are not specified,
- The program stops if a severe error is encountered.
- The program continues to the next statement if a recoverable error is
encountered and the ERR_RECOVERY run-time option is set to
YES. If the option is set to NO, the program
stops.
- The program continues to the next statement when a conversion error is
encountered if the ERR_RECOVERY run-time option is set to
YES. If the CNVERR run-time option is set to
YES, conversion errors are treated as recoverable errors; if
CNVERR=NO, they are treated as conversion errors.
+----------------------------End of IBM Extension----------------------------+
Examples
INTEGER A(100)
CHARACTER*4 B
READ *, A(LBOUND(A,1):UBOUND(A,1))
READ (7,FMT='(A3)',ADVANCE='NO',EOR=100) B
·
·
·
100 PRINT *, 'end of record reached'
END
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