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ABAP Keyword Documentation → ABAP − Reference → Processing External Data → ABAP File Interface → Statements for the ABAP File Interface →Syntax
READ DATASET dset INTO dobj [MAXIMUM LENGTH mlen]
[[ACTUAL] LENGTH alen].
Extras:
1. ... MAXIMUM LENGTH mlen
2. ... [ACTUAL] LENGTH alen
Effect
This statement exports data from the file specified in dset to the data object dobj. dobj expects variables with elementary data types and flat structures. In Unicode programs, dobj must be character-like if the file was opened as a text file.
dset expects a character-like data object containing the physical name of the file. The content is read from the file starting from the current file pointer. After the data is passed, the file pointer is positioned after the section that was read. Using the MAXIMUM LENGTH addition, the number of characters or bytes to be read from the file can be limited. Using ACTUAL LENGTH, the number of characters or bytes actually used can be determined.
In a Unicode program, the file must be opened with an arbitrary access type; otherwise, an exception that cannot be handled is raised.
If the file was not yet opened in a non-Unicode program, it is implicitly opened using the statement
OPEN DATASET dset FOR INPUT IN BINARY MODE
as a binary file for writing. If the system accesses a nonexistent file, a handleable exception is raised.
The Influence of Access Type
Files can be read independently of the access type.
Whether data can be read or not depends solely on the position of the file pointer. If the latter is
at the end of the file or after the file, no data can be read and sy-subrc will be set to 4.
Influence of the Storage Type
The import function works irrespective of the storage type in which the file was opened using the statement OPEN DATASET.
If the file was opened as a text file or as a legacy text file, the data is normally read from the current position of the file pointer to the next end-of-line marking, and the file pointer is positioned after the end-of-line marking. If the data object dobj is too short for the number of read characters, the superfluous characters and bytes are cut off. If it is longer, it is padded with blanks on the right.
If the file was opened as a binary file or as a legacy binary file, as much data is read that fits into the data object dobj. If the data object dobj is longer than the number of exported characters, it is padded with hexadecimal 0 on the right.
If the specified storage type makes conversion necessary, this is executed before the assignment to
the data object dobj. Afterwards, the read data is placed, byte by byte, into the data object.
System Fields
sy-subrc | Meaning |
0 | Data was read without reaching end of file. |
4 | Data was read and the end of the file was reached or there was an attempt to read after the end of the file. |
Notes
Example
Importing the binary file flights.dat written in the example by the TRANSFER statement. The data is written (in binary) to a byte-like typed field symbol <hex_container>. Using the assignment of the structured data area wa to the field symbol, this adopts the length of the data area and a corresponding number of bytes for the loop process are imported. It would be possible to import directly into the structure wa with the same result, but the use of the field symbol is the recommended procedure. The reason is that in this way data is explicitly transferred from a binary file into a binary data type.
DATA: file TYPE string VALUE `flights.dat`,
wa TYPE spfli,
itab LIKE TABLE OF wa.
FIELD-SYMBOLS <hex_container> TYPE x.
OPEN DATASET file FOR INPUT IN BINARY MODE.
ASSIGN wa TO <hex_container> CASTING.
DO.
READ DATASET file INTO <hex_container>.
IF sy-subrc = 0.
APPEND wa TO itab.
ELSE.
EXIT.
ENDIF.
ENDDO.
CLOSE DATASET file.
cl_demo_output=>display_data( itab ).
... MAXIMUM LENGTH mlen
Effect
This addition determines how many characters or how many bytes at most are read from the file. mlen expects a data object of the type i. It contains the number of characters or bytes. In the case of text files, the content of mlen determines how many characters are read from the file. In the case of binary files, legacy text files, and legacy binary files, mlen determines how many bytes are read from the file.
The first mlen characters or bytes are read from the current position of the file pointer and the file pointer is positioned after the read file. If the file is opened as a (legacy) text file and there isan end-of-line marking within the specified length, data is read only up to this position and the file pointer is positioned after the end-of-line marking.
If the value of mlen is the same as 0, no data is read. If the value of
mlen is negative, the addition is ignored and the import takes place in the same way as described for Influence of Storage Type.
Note
In case of text files, the number of bytes read depends on the character format specified using ENCODING when opening the file.
Example
This program section has the same functions as the previous example. Here data is imported not into a byte-like field symbol, but into a byte-like data object hex_container. The number of bytes to be imported is determined by the typed field symbol <spfli>.
DATA: file TYPE string VALUE `flights.dat`,
hex_container TYPE x LENGTH 1000,
len TYPE i,
itab TYPE TABLE OF spfli.
FIELD-SYMBOLS <spfli> TYPE spfli.
DESCRIBE FIELD <spfli> LENGTH len IN BYTE MODE.
OPEN DATASET file FOR INPUT IN BINARY MODE.
ASSIGN hex_container TO <spfli> CASTING.
DO.
READ DATASET file INTO hex_container MAXIMUM LENGTH len.
IF sy-subrc = 0.
APPEND <spfli> TO itab.
ELSE.
EXIT.
ENDIF.
ENDDO.
CLOSE DATASET file.
cl_demo_output=>display_data( itab ).
... [ACTUAL] LENGTH alen
Effect
This addition assigns the number of characters or bytes to be read from the file to the data object alen. The following can be specified for alen:
For text files, the system determines how many characters were written to the memory area. For binary
files, legacy text files, and legacy binary files, the system determines how many bytes were read from the file.
Notes
Catchable Exceptions
CX_SY_CODEPAGE_CONVERTER_INIT
CX_SY_CONVERSION_CODEPAGE
CX_SY_FILE_AUTHORITY
CX_SY_FILE_IO
CX_SY_FILE_OPEN
CX_SY_FILE_OPEN_MODE
CX_SY_PIPE_REOPEN