ABAP Keyword Documentation → ABAP - Reference → Obsolete Language Elements → Obsolete data and communication interfaces → CPI-C Interface
COMMUNICATION
Other versions: 7.31 | 7.40 | 7.54
Obsolete Syntax
COMMUNICATION comstep ID id [cpic_options].
Effect
This statement enables cross-system communication between two ABAP programs, or between an ABAP program
and a program written in another programming language. The whole communication process takes place in
individual communication steps, which involve repeated execution of the COMMUNICATION
statement with the corresponding additions comstep. For both partner programs, communication is based on the
CPI-C interface, which has been
defined as a communication standard by IBM as a part of the SAA standard. This interface provides the following functions in the form of the CPI-C starter set:
- Creating, accepting, and closing a connection
-
Sending and receiving data
Coordination of the individual communication steps, recording any errors that occur in the database table TCPIC and, if necessary, data conversion, take place in the individual programs themselves. The parameters that determined the physical partner system for a connection are administrated in the database table TXCOM.
Once the connection is initialized, the system writes an eight-digit connection number in the data object
id. This number can be used to identify individual connections. As standard, 2**16 connections are possible for each calling program. id expects only
flat character-like data types, with a minimum length of eight digits.
After initialization, the connection must be created. Then, in the first connection step, all the necessary administration data is sent to the partner system. The data sent in this connection step must have a specific structure and must be available in an EBCDIC format. The example below shows how a specifically formed structure can be converted into the EBCDIC format. The subsequent response also exists in EBCDIC format. After this initial connection has been established, data can be transferred without the need for further conversion.
In communications, the internal
session in the called program must not be changed. Screen output is ignored or, in the case of list output to the SAP spool system, is diverted if the statement NEW-PAGE is entered beforehand.
Messages of types I, S, and W are ignored, while types A and E cause the program to terminate.
Notes
-
The statement
COMMUNICATIONis not supported in classes and should not appear in programs anymore, since support for the direct programming of the CPI-C interface has largely been discontinued. Instead, only the RFC interface is to be used for communication between programs. However, the function of the statement is maintained for supporting existing programs and for internal purposes. -
The EBCDIC format is used in the first connection step because the CPI-C interface was mainly used for connections to R/2 systems.
Example
In the simplest case, an ABAP program calls a subroutine in an ABAP program of another AS ABAP. To enable this, the calling program must register on the other system by specifying the type of CPI-C service, the logon data, the programs and subroutines, and the type of error handling. The registration is performed by sending a specific structure to the other system in EBCDIC format.
The following example shows a schematic representation of the communication between two ABAP programs
P1 and P2 without querying return values. The calling program P1 first creates the connection and sends
a field connect_xstr that contains the content of the connect
structure converted into EBCDIC format, with the necessary data. After the connection is confirmed by
P2, P1 sends the actual, unconverted application data in the buffer b. When this data has been received, P2 sends a confirmation to P1. The connection from P1 is then closed again and the content of the buffer
("Answer") is produced as output.
PROGRAM p1. DATA: d TYPE c LENGTH 8,
id TYPE c LENGTH 8, b TYPE c LENGTH 10,
len TYPE x LENGTH 4, dat TYPE xstring,
stat TYPE xstring, BEGIN OF connect,
header TYPE c LENGTH 12 VALUE 'CONNCPIC1',
client TYPE c LENGTH 3 VALUE '001',
user TYPE c LENGTH 12 VALUE 'BONDJ',
password TYPE c LENGTH 8 VALUE '007',
language TYPE c LENGTH 1 VALUE 'E',
corr TYPE c LENGTH 1 VALUE ' ',
program TYPE c LENGTH 8 VALUE 'P2',
routine TYPE c LENGTH 30 VALUE 'CPIC_START',
END OF connect, connect_str TYPE c LENGTH 75,
connect_xstr TYPE x LENGTH 75,
connect_ret TYPE x LENGTH 75, converter TYPE REF TO cl_abap_conv_out_ce.
connect_str = connect. converter = cl_abap_conv_out_ce=>create( encoding = '0101' ).
converter->write( data = connect_str ). connect_xstr = converter->get_buffer( ).
d = ...
COMMUNICATION INIT DESTINATION d
ID id. COMMUNICATION ALLOCATE
ID id. COMMUNICATION SEND
BUFFER connect_xstr ID id.
PROGRAM p2.
DATA:
id TYPE c LENGTH 8,
b TYPE c LENGTH 10,
len TYPE x LENGTH 4,
dat TYPE xstring,
stat TYPE xstring.
FORM cpic_start.
COMMUNICATION ACCEPT
ID id.
COMMUNICATION RECEIVE BUFFER connect_ret
DATAINFO dat STATUSINFO stat
RECEIVED len ID id.
b = 'Request'. COMMUNICATION SEND BUFFER b
ID id.
COMMUNICATION RECEIVE
BUFFER b
RECEIVED len
DATAINFO dat
STATUSINFO stat
ID id.
IF b = 'Request'.
b = 'Answer'.
ENDIF.
COMMUNICATION SEND
BUFFER b
ID id.
ENDFORM.
CLEAR b. COMMUNICATION RECEIVE BUFFER b
DATAINFO dat STATUSINFO stat
RECEIVED len ID id.
WRITE / b.
COMMUNICATION DEALLOCATE ID id.
Exceptions
Non-Catchable Exceptions
-
Cause: No authorization to accept a CPIC connection.
Runtime Error:COMMUNICATION_ACCEPT_NO_AUTH -
Cause: No authorization to open a CPIC connection.
Runtime Error:COMMUNICATION_INIT_NO_AUTH