Using a VIEW Typed Buffer

There are two kinds of VIEW typed buffers. The first, FML VIEW, is a C structure generated from an FML buffer. The second is simply an independent C structure.

The reason for converting FML buffers into C structures and back again (and the purpose of the FML VIEW typed buffers) is that while FML buffers provide data-independence and convenience, they incur processing overhead because they must be manipulated using FML function calls. C structures, while not providing flexibility, offer the performance required for lengthy manipulations of buffer data. If you need to perform a significant amount of data manipulation, you can improve performance by transferring fielded buffer data to C structures, operating on the data using normal C functions, and then converting the data back to the FML buffer for storage or message transmission.

For more information on the FML typed buffer and FML file conversion, refer to the BEA Tuxedo ATMI FML Function Reference.

To use VIEW typed buffers, you must perform the following steps:

Setting Environment Variables for a VIEW Typed Buffer

To use a VIEW typed buffer in an application, you must set the following environment variables.

Environment Variables for a VIEW Typed Buffer

Environment Variable	Description
FIELDTBLS or FIELDTBLS32	Comma-separated list of field table filenames for FML or FML32 typed buffers. Required only for FML VIEW types.
FLDTBLDIR or FLDTBLDIR32	Colon-separated list of directories to search for the field table files for FML and FML32 typed buffers. For Microsoft Windows, use a semicolon-separated list. Required only for FML VIEW types.
VIEWFILES or VIEWFILES32	Comma-separated list of allowable filenames for VIEW or VIEW32 description files.
VIEWDIR or VIEWDIR32	Colon-separated list of directories to search for VIEW or VIEW32 files. For Microsoft Windows, use a semicolon-separated list.

To use a VIEW typed buffer, you must define the C record in a view description file. The view description file includes, a view for each entry, a view that describes the characteristic C structure mapping and the potential FML conversion pattern. The name of the view corresponds to the name of the C language structure.

The following format is used for each structure in the view description file:

$ /* View structure */
VIEW viewname
type cname fbname count flag size null

The following table describes the fields that must be specified in the view description file for each C structure.

View Description File Fields

You can include a comment line by prefixing it with the # or $ character. Lines prefixed by a $ sign are included in the .h file.

View Description File for FML VIEW

$ /* View structure */
  VIEW MYVIEW
  #type    cname     fbname   count   flag    size    null
  float    float1    FLOAT1    1       -       -       0.0
  double   double1   DOUBLE1   1       -       -       0.0
  long     long1     LONG1     1       -       -       0
  short    short1    SHORT1    1       -       -       0
  int      int1      INT1      1       -       -       0
  dec_t    dec1      DEC1      1       -       9,16    0
  char     char1     CHAR1     1       -       -       '\0'
  string   string1   STRING1   1       -       20      '\0'
  carray   carray1   CARRAY1   2       CL      20      '\0'
  END

The following listing illustrates the same view description file for an independent VIEW.

View Description File for an Independent View

$ /* View data structure */
  VIEW MYVIEW
  #type   cname   fbname  count   flag    size    null
  float   float1  -       1       -       -       -
  double  double1 -       1       -       -       -
  long    long1   -       1       -       -       -
  short   short1  -       1       -       -       -
  int     int1    -       1       -       -       -
  dec_t   dec1    -       1       -       9,16    -
  char    char1   -       1       -       -       -
  string  string1 -       1       -       20      -
  carray  carray1 -       2       CL      20      -
  END

Executing the VIEW Compiler

To compile a VIEW typed buffer, run the viewc command, specifying the name of the view description file as an argument. To specify an independent VIEW, use the -n option. You can optionally specify a directory in which the resulting output file should be written. By default, the output file is written to the current directory.

For example, for an FML-dependent VIEW, the compiler is invoked as follows:

viewc myview.v

Note: To compile a VIEW32 typed buffer, run the viewc32 command.

For an independent VIEW, use the -n option on the command line, as follows:

viewc -n myview.v

The output of the viewc command includes:

The following listing provides an example of the header file created by viewc.

Header File Created Using the VIEW Compiler

struct MYVIEW {
  float   float1;
  double  double1;
  long    long1;
  short   short1;
  int     int1;
  dec_t   dec1;
  char    char1;
  char    string1[20];
  unsigned short L_carray1[2];    /* length array of carray1 */
  short   C_carray1;              /* count of carray1 */
  char    carray1[2][20];
};

The same header file is created for FML-dependent and independent VIEWs.

In order to use a VIEW typed buffer in client programs or service subroutines, you must specify the header file in the application #include statements.

See Also