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Visual
Basic Integration
Fujitsu COBOL provides three methods to share applications
and data with Visual Basic: Dynamic-Link Libraries (DLLs),
Dynamic Data Exchange (DDE), and Object Linking and Embedding
(OLE).
Fujitsu
COBOL also provides support for Embedded Structured Query
Language (ESQL), compatible with either Microsoft SQL Server,
Oracle 7, or Sybase to allow access to data on remote servers.
Thus, programmers are no longer restricted to accessing data
sequentially. They can take advantage of SQL server's sophisticated
relational database management system. Integrating the three
languages, you can create distributed client-server applications
with a sophisticated graphical user interface.
With support
for Visual Basic and SQL Server, Fujitsu COBOL makes the possibility
of downsizing large mainframe applications to Windows a reality.
COBOL
DLL Interaction with Visual Basic
To access any COBOL routines from Visual Basic, you need to
first declare the COBOL PROGRAM-ID or the COBOL ENTRY routine
using the Basic Declare statement with the special Lib keyword
to specify the path name of the COBOL DLL. These declarations
can be made in the declaration section of any form module
or in the global module. You can then call these routines
from your Visual Basic code like any other function call.
When a
Visual Basic program calls a COBOL routine, you should call
JMPCINT2 before calling the first COBOL routine, and call
JMPCINT3 after calling the last COBOL routine. JMPCINT2 is
a subroutine that initializes the COBOL Run Time Environment
and JMPCINT3 is a subroutine that terminates the COBOL Run
Time Environment.
Visual
Basic Declaration
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Declare
Sub MYCOBOL Lib "c:\mycobol.dll" (vbInteger as Integer,
ByVal vbString as String)
Declare Sub JMPCINT2 Lib "c:\FSC\PCOBOL32\F3BIPRCT.DLL"
()
Declare Sub JMPCINT3 Lib "c:\FSC\PCOBOL32\F3BIPRCT.DLL"
()
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Visual Basic Call
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Sub
Form_Click ( )
Dim vbInteger as Integer
Dim vbString as string * 15
Call JMPCINT2 ' Initialize COBOL Runtime Environment
Call MYCOBOL (vbInteger, vbString)
Call JMPCINT3 ' Terminate COBOL Runtime Environment
End Sub
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COBOL
Linkage and Procedure Division
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Identification
Division.
Program-ID. "MYCOBOL".
Data Division.
Linkage Section.
01 vbInteger pic s9(4) comp-5.
01 vbString pic x(15).
Procedure Division with STDCALL Linkage Using vbInteger,
vbString.
move 100 to vbInteger
move "Fujitsu COBOL" to vbString
exit program.
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Parameter
Passing Between Visual Basic and Fujitsu COBOL
Visual Basic treats a COBOL DLL as a "black box." It
only needs to know the COBOL program's LINKAGE SECTION parameter
list to pass data to and from the COBOL DLL. Parameters can
only be passed from Visual Basic to COBOL BY REFERENCE, except
strings that must be passed using the ByVal keyword in the
Declare statement. Passing parameters BY REFERENCE is the
default in Visual Basic. Parameter names need not be the same
between Visual Basic and COBOL, however, attribute, length,
and number of corresponding data items, must be identical.
Visual
Basic declarations must exactly match the COBOL parameter
lists defined in the USING statement of the COBOL PROCEDURE
DIVISION or ENTRY statements. No parameter checking is done
because the two are separate compilation units.
Visual
Basic incorporates a rich assortment of data types, some of
which are currently not supported by Fujitsu COBOL. These
data types include variable-length strings, Currency, Variants,
and objects.
Visual
Basic Strings
All strings passed between Visual Basic and COBOL must
be declared as fixed-length strings and passed using the ByVal
keyword in the Declare statement. To avoid possible memory
corruption, ensure that all strings passed between Visual
Basic and COBOL occupy the same size.
Dim vbString
as string * 15 ' Equivalent to PIC X(15)
When passing
parameters, associate the data types as follows:
| Visual
Basic |
COBOL |
| Type
Name |
Storage
Size |
PICTURE
Clause |
| Boolean
(16-bit) |
2
Bytes
|
S9(4)
COMP-5 |
| Boolean
(32-bit) |
4
Bytes |
S9(9)
COMP-5 |
| Byte |
1
Byte |
X |
| Double |
8
Bytes |
COMP-2 |
| Integer |
2
Bytes |
S9(4)
COMP-5 |
| Long |
4
Bytes |
S9(9)
COMP-5 |
| Single |
4
Bytes |
COMP-1 |
| String |
1
Byte per Character |
X(n) |
Passing Arrays
Visual Basic and COBOL can pass numeric arrays. This works
because numeric array data is always laid out sequentially
in memory. A COBOL routine, if given the first element of
an array, has access to all of its elements.
Returning
Control and Terminating Programs
To return control from COBOL to Visual Basic, execute
the EXIT PROGRAM statement. When the EXIT PROGRAM statement
is executed, control returns immediately to the calling program.
Compiling
and Linking the COBOL Programs
To build the COBOL DLL, you need to create a module definition
file (.DEF) that lists the attributes of the DLL library.
A proper DEF file will be automatically created by the COBOL
Project Manager, included with Fujitsu COBOL, during the build
process, or you can modify the following example below changing
the MYCOBOL to match the COBOL PROGRAM-ID
Sample
COBOL.DEF
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LIBRARY
"MYCOBOL"
EXPORTS MYCOBOL
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Reuse vs Rewrite
