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This document covers the following topics:

• Function

• Syntax Description

• Return Code

• User Exits

• INTERFACE4

For an explanation of the symbols used in the syntax diagram, see Syntax Symbols.

Related Statements: CALL FILE | CALL LOOP | CALLNAT | DEFINE SUBROUTINE | ESCAPE | FETCH | PERFORM

Belongs to Function Group: Invoking Programs and Routines

Function

The CALL statement is used to call an external program or function written in another standard programming language from a Natural program and then return to the next statement after the CALL statement.

The called program or function may be written in any programming language which supports a standard CALL interface. Multiple CALL statements to one or more external program or functions may be specified.

Syntax Description

Operand Definition Table:

Syntax Element Description:

Return Code

The condition code of any called function may be obtained by using the Natural system function RET (Return Code Function).

Example:

... 
RESET #RETURN(B4) 
CALL 'PROG1' 
IF RET ('PROG1') > #RETURN 
  WRITE 'ERROR OCCURRED IN PROGRAM1' 
END-IF 
...

User Exits

User exits are needed to make external functions available and to access operating-system interfaces that are not available to Natural.

The user exits can be placed either in a shared library and thus linked dynamically, or in a library that is linked statically to the Natural nucleus.

If they are placed in shared libraries, it is not necessary to relink Natural whenever a user exit is modified. This makes the development and testing of user exits a lot easier. This feature is available under all operating systems that support shared libraries. Under all operating systems, it is possible to place user exits in a library that is linked to the Natural nucleus; that is, to statically link the user exits with the Natural prelinked object natraw.o.

A user exit is added to Natural in three steps:

1. A jump table has to be created that allows Natural to associate the name of a function invoked by a CALL statement with the address of the function.

2. The functions that were put into the jump table must be written.

3. In the case of a dynamic link, the shared library that contains the user exits has to be rebuilt. In the case of a static link, the jump table and the external functions must be linked together with the prelinked Natural nucleus, to produce an executable Natural nucleus that supports the external functions.

The following topics are covered below:

• Step 1 - Defining the Jump Table

• Step 2 - Writing the External Functions

• Step 3 - Compiling and Linking

• How to Build a Shared Library

• Using the Shared Library

• How to Generate a Static Nucleus

• Example Programs

Step 1 - Defining the Jump Table

A sample of a jump table - jumptab.c - can be found in the directory:

$NATDIR/$NATVERS/samples/sysexuex

Step 2 - Writing the External Functions

Each function has three parameters and returns a long integer. A function prototype should be as follows:

NATFCT myadd  (nparm, parmptr, parmdec)


WORD  nparm; 
BYTE  **parmptr; 
FINFO  *parmdec;

The data type FINFO is defined as follows:

typedef struct { 
  unsigned char     TypeVar;      /* type of variable                       */ 
  unsigned char     pb2;          /* if type == ('D', 'N', 'P' or 'T') ==>  */ 
                                  /*    total num of digits                 */ 
                                  /* else                                   */ 
  union {                         /*    unused                              */ 
    unsigned char   pb[2];        /* if type == ('D', 'N', 'P' or 'T') ==>  */ 
    unsigned short  lfield;       /*    pb[0] = #dig before.dec.point       */ 
  } flen;                         /*    pb[1] = #dig  after.dec.point       */ 
                                  /* else                                   */ 
                                  /*    lfield = length of field            */ 
} FINFO;

Next, the module containing the external functions must be written. A sample function - mycadd.c - can be found in the directory:

$NATDIR/$NATVERS/samples/sysexuex

Step 3 - Compiling and Linking

The file natuser.h, which is included by the sample program, is delivered with Natural. It contains declarations for the data types BYTE, WORD and the FINFO structure, that is, the description of the internal representation of each passed parameter.

• In the case of dynamically linked user exits, the shared library containing the user exits has to be rebuilt.

• In the case of statically linked user exits, the Natural nucleus has to be relinked.

For these purposes, it is strongly recommended to use the sample makefiles supplied by Software AG, as they already contain the necessary compiler and linker parameters. The sample makefiles can be found in the directory:

$NATDIR/$NATVERS/samples/sysexuex

For further information, see the following sections and the explanations in the makefiles themselves.

How to Build a Shared Library

1. From the example directory, which is contained in $NATDIR/$NATVERS/samples/sysexuex, copy the following files into your work directory:

   • Makedyn

   • jumptab.c

   • ncuxinit.c

2. Copy the C source files which contain your user exits into the same work directory.

3. Edit the file jumptab.c to include the names and function pointers for your user exits. To do so, you add in Section 2 the external declarations of your user exits, and in Section 3 you add the name/function-pointer pairs for your user exits. You might consider cutting and pasting the appropriate sections from your pre-2.2 version of jumptab.c.

4. Edit the makefile as follows:

   • Specify the names of the object files containing the user exits in the following line:

     USEROBJS =

   • Specify the name of the resulting shared library in the following line:

     USERLIB =

   • If you need to include private header files, specify the directories containing them in the following line:

     INCDIR =

5. To remove all unneeded files, issue the command:

   make -f Makedyn clean

6. To compile and link your shared library, issue the command:

   make -f Makedyn lib

Using the Shared Library

Set the environment variable NATUSER to the libraries you want to use. For example:

setenv NATUSER $NATDIR/$NATVERS/bin/library-name

You must specify a full qualified path name for the shared library.

You can specify more than one path if you delimit them with a colon (:) similar to the UNIX PATH variable.

Note:
The libraries are searched in the order in which they are specified in NATUSER. This means that if two libraries contain a function of the same name, Natural always calls the function in the library which is specified first in NATUSER.

Example:

See the sample user exit function in $NATDIR/$NATVERS/samples/sysexuex.

How to Generate a Static Nucleus

1. From the example directory, which is contained in $NATDIR/$NATVERS/samples/sysexuex, copy the following files into your work directory:

   • Makefile

   • jumptab.c

2. Copy the C source files which contain your user exits into the same work directory.

3. Edit the file jumptab.c to include the names and function pointers for your user exits. To do so, you add in Section 2 the external declarations of your user exits, and in Section 3 you add the name/function-pointer pairs for your user exits. You might consider cutting and pasting the appropriate sections from your pre-2.2 version of jumptab.c.

4. Edit the makefile as follows:

   • Specify the names of the object files containing the user exits in the following line:

     USEROBJS = 

   • If you need to include private header files, specify the directories containing them in the following line:

     INCDIR =

5. Issue the command make to get information about further processing options.

Example:

See the sample user exit function in $NATDIR/$NATVERS/samples/sysexuex.

Example Programs

After successful compilation and linking, the external programs can be invoked from a Natural program. Corresponding Natural example programs are provided in the library SYSEXUEX.

INTERFACE4

The keyword INTERFACE4 specifies the type of the interface that is used for the call of the external program. This keyword is optional. If this keyword is specified, the interface, which is defined as INTERFACE4, is used for the call of the external program.

The following table lists the differences between the CALL statement used with INTERFACE4 and the one used without INTERFACE4:

The following topics are covered below:

• INTERFACE4 - External 3GL Program Interface

• Operand Structure for INTERFACE4

• INTERFACE4 - Parameter Access

• Exported Functions

INTERFACE4 - External 3GL Program Interface

The interface of the external 3GL program is defined as follows, when INTERFACE4 is specified with the Natural CALL statement:

NATFCT functionname (numparm, parmhandle, traditional)

Operand Structure for INTERFACE4

The operand structure of INTERFACE4 is named parameter_description and is defined as follows. The structure is delivered with the header file natuser.h.

The address element is null for arrays of dynamic variables and for X-arrays. In these cases, the array data cannot be accessed as a whole, but must be accessed through the parameter access functions described below.

For arrays with fixed bounds of variables with fixed length, the array contents can be accessed directly using the address element. In these cases the address of an array element (i,j,k) is computed as follows (especially if the array elements are not contiguous):

elementaddress = address + i * indexfactors[0] + j * indexfactors[1] + k * indexfactors[2]

If the array has less than 3 dimensions, leave out the last terms.

INTERFACE4 - Parameter Access

A set of functions is available to be used for the access of the parameters. The process flow is as follows:

• The 3GL program is called via the CALL statement with the INTERFACE4 option, and the parameters are passed to the 3GL program as described above.

• The 3GL program can now use the exported functions of Natural, to retrieve either the parameter data itself, or information about the parameter, such as format, length, array information, etc.

• The exported functions can also be used to pass back parameter data.

There are also functions to create and initialize a new parameter set in order to call arbitrary subprograms from a 3GL program. With this technique a parameter access is guaranteed to avoid memory overwrites done by the 3GL program. (Natural's data is safe: memory overwrites within the 3GL program's data are still possible).

Exported Functions

The following topics are covered below:

• Get Parameter Information
• Get Parameter Data
• Write Back Operand Data
• Create, Initialize and Delete a Parameter Set
• Create Parameter Set
• Delete Parameter Set
• Initialize a Scalar of a Static Data Type
• Initialize an Array of a Static Data Type
• Initialize a Scalar of a Dynamic Data Type
• Initialize an Array of a Dynamic Data Type
• Resize an X-array Parameter

Get Parameter Information

This function is used by the 3GL program to receive all necessary information from any parameter. This information is returned in the struct parameter_description, which is documented above.

Prototype:

int ncxr_get_parm_info ( int parmnum, void *parmhandle, struct parameter_description *descr );

Parameter Description:

Get Parameter Data

This function is used by the 3GL program to get the data from any parameter.

Natural identifies the parameter by the given parameter number and writes the parameter data to the given buffer address with the given buffer size.

If the parameter data is longer than the given buffer size, Natural will truncate the data to the given length. The external 3GL program can make use of the function ncxr_get_parm_info, to request the length of the parameter data.

There are two functions to get parameter data: ncxr_get_parm gets the whole parameter (even if the parameter is an array), whereas ncxr_get_parm_array gets the specified array element.

If no memory of the indicated size is allocated for "buffer" by the 3GL program (dynamically or statically), results of the operation are unpredictable. Natural will only check for a null pointer.

If data gets truncated for variables of the type I2/I4/F4/F8 (buffer length not equal to the total parameter length), the results depend on the machine type (little endian/big endian). In some applications, the user exit must be programmed to use no static data to make recursion possible.

Prototypes:

int ncxr_get_parm( int parmnum, void *parmhandle, int buffer_length, void *buffer )

int ncxr_get_parm_array( int parmnum, void *parmhandle, int buffer_length, void *buffer, int *indexes )

This function is identical to ncxr_get_parm, except that the indexes for each dimension can be specified. The indexes for unused dimensions should be specified as 0.

Parameter Description:

Write Back Operand Data

These functions are used by the 3GL program to write back the data to any parameter. Natural identifies the parameter by the given parameter number and writes the parameter data from the given buffer address with the given buffer size to the parameter data. If the parameter data is shorter than the given buffer size, the data will be truncated to the parameters data length, that is, the rest of the buffer will be ignored. If the parameter data is longer than the given buffer size, the data will be copied only to the given buffer length, the rest of the parameter stays untouched. This applies to arrays in the same way. For dynamic variables as parameters, the parameter is resized to the given buffer length.

If data gets truncated for variables of the type I2/I4/F4/F8 (buffer length not equal to the total parameter length), the results depend on the machine type (little endian/big endian). In some applications, the user exit must be programmed to use no static data to make recursion possible.

Prototypes:

int ncxr_put_parm        ( int parmnum, void *parmhandle,
                             int buffer_length, void *buffer );
int ncxr_put_parm_array  ( int parmnum, void *parmhandle, 
                            int buffer_length, void *buffer,
                           int *indexes );

Parameter Description:

Create, Initialize and Delete a Parameter Set

If a 3GL program wants to call a Natural subprogram, it needs to build a parameter set that corresponds to the parameters the subprogram expects. The function ncxr_create_parm is used to create a set of parameters to be passed with a call to ncxr_if_callnat. The set of parameters created is represented by an opaque parameter handle, like the parameter set that is passed to the 3GL program with the CALL INTERFACE4 statement. Thus, the newly created parameter set can be manipulated with functions ncxr_put_parm* and ncxr_get_parm* as described above.

The newly created parameter set is not yet initialized after having called the function ncxr_create_parm. An individual parameter is initialized to a specific data type by a set of ncxr_parm_init* functions described below. The functions ncxr_put_parm* and ncxr_get_parm* are then used to access the contents of each individual parameter. After the caller has finished with the parameter set, they must delete the parameter handle. Thus, a typical sequence in creating and using a set of parameters for a subprogram to be called through ncxr_if4_callnat will be:

ncxr_create_parm
ncxr_init_ parm*
ncxr_init_ parm*
...
ncxr_put_ parm*
ncxr_put_ parm*
...
ncxr_get_parm_info*
ncxr_get_parm_info*
...
ncxr_if4_callnat
...
ncxr_get_parm_info*
ncxr_get_parm_info*
...
ncxr_get_ parm*
ncxr_get_ parm*
...
ncxr_delete_parm

Create Parameter Set

The function ncxr_create_parm is used to create a set of parameters to be passed with a call to ncxr_if_callnat.

Prototype:

int ncxr_create_parm( int parmnum, void** pparmhandle )

Parameter Description:

Delete Parameter Set

The function ncxr_delete_parm is used to delete a set of parameters that was created with ncxr_create_parm.

Prototype:

int ncxr_delete_parm( void* parmhandle )

Parameter Description:

Initialize a Scalar of a Static Data Type

Prototype:

int ncxr_init_parm_s( int parmnum, void *parmhandle,
    char format, int length, int precision, int flags );

Parameter Description:

Initialize an Array of a Static Data Type

Prototype:

int ncxr_init_parm_sa( int parmnum, void *parmhandle,
    char format, int length, int precision,
    int dim, int *occ, int flags );

Parameter Description:

Initialize a Scalar of a Dynamic Data Type

Prototype:

int ncxr_init_parm_d( int parmnum, void *parmhandle, 
    char format, int flags );

Parameter Description:

Initialize an Array of a Dynamic Data Type

Prototype:

int ncxr_init_parm_da( int parmnum, void *parmhandle,
    char format, int dim, int *occ, int flags );

Parameter Description:

Resize an X-array Parameter

Prototype:

int ncxr_resize_parm_array( int parmnum, void *parmhandle, int *occ );

Parameter Description:

All function prototypes are declared in the file natuser.h.

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