4. Field Definition and Use

Introduction

Before you can begin to work with FML fielded buffers, or use the VIEWS functions that move fields between structures and fielded buffers, certain details must be taken care of, such as:

defining fields
making field definitions available to applications programs (through field table files and mapping functions at run-time, or C header files at compile time)
compiling source view descriptions into object view descriptions, and generating corresponding C header files and COBOL COPY files

Defining Fields

This section discusses

how fields are defined in field tables for run-time use
the available functions for run-time use with the field table files

Field Names and Identifiers

A field identifier (fieldid) is defined (typedef'd) as a FLDID (FLDID32 for FML32), and is composed of two parts: a field type and a field number (the number uniquely identifies the field).

Field numbers are restricted to be between 1 and 8191, inclusive, for FML, and between 1 and 33,554,431, inclusive, for FML32. Field number 0 and the corresponding field identifier 0 is reserved to indicate a bad field identifier (BADFLDID). When FML is used with other software that also uses fields, additional restrictions may be imposed on field numbers.

The numbering convention adopted by the BEA TUXEDO system is as follows:

field numbers 1-100 are reserved for system use
field numbers 101-8191 are for application-defined fields with FML, and field numbers 101-33,554,431 for FML32.

The mappings between field identifiers and field names are contained in either field table files or field header files. Using field table files requires that you convert field name references in C programs with the mapping functions described later in this chapter; field header files allow the C preprocessor (cpp(1) in UNIX reference manuals) to resolve name-to-fieldid mappings when a program is compiled.

The functions and programs that access field tables use the environment variables FLDTBLDIR and FIELDTBLS to specify the source directories and field table files, respectively, which are to be used (FLDTBLDIR32 and FIELDTBLS32 are used for FML32). These should be set as described in Chapter 3, "Setup."

The use of multiple field tables allows you to establish separate directories and/or files for separate groups of fields. Note that field names and field numbers should be unique across all field tables, since such tables are capable of being converted into C header files, and field numbers that occur more than once may cause unpredictable results.

Field Table Files

Field table files are created using a standard text editor, such as vi. They have the following format:

Blank lines and lines beginning with # are ignored.
Lines beginning with $ ignored by the mapping functions but are passed through (without the $) to header files generated by mkfldhdr(1); for example, this would allow the application to pass C comments, what strings, etc. to the generated C header file; they are not passed through to the COBOL copy files.
Lines beginning with the string *base contain a base for offsetting subsequent field numbers; this optional feature provides an easy way to group and renumber sets of related fields.

All other lines should have the following form.

name       rel-number      type      flag      comment

where:

Note that these entries must be separated by white space (blanks or tabs).

Field Table Example

The following is an example field table in which the base shifts from 500 to 700. The first fields in each group will be numbered 501 and 701, respectively.

Listing 4-1 A UNIX Field Table File

# following are fields for EMPLOYEE service
# employee ID fields are based at 500
*base 500
#name           rel-number      type           flags   comment
#----           ----------      ----           ------  -------
EMPNAME         1               string         -       emp name
EMPID           2               long           -       emp id
EMPJOB          3               char           -       job type
SRVCDAY         4               carray         -       service date
*base 700
# all address fields are now relative to 700
EMPADDR         1               string         -       street address
EMPCITY         2               string         -       city
EMPSTATE        3               string         -       state
EMPZIP          4               long           -       zip code

Mapping Functions

Run-time mapping is done by the Fldid() and Fname() functions that consult the set of field table files specified by the FLDTBLDIR and FIELDTBLS environment variables (Fldid32() and Fname32() reference FLDTBLDIR32 and FIELDTBLS32 for FML32).

Fldid maps its argument, a field name, to a fieldid:

char *name;
extern FLDID Fldid();
FLDID id;
...
id = Fldid(name);

Fname does the reverse translation by mapping its argument, a fieldid, to a field name:

extern char *Fname();
name = Fname(id);
. . .

The identifier-to-name mapping is rarely used; that is, it is rare that one has a field identifier and wants to know the corresponding name. One place where the field identifier-to-field name mapping could be used is in a buffer print routine where you want to display, in an intelligible form, the contents of a fielded buffer.

Loading the Field Tables

Upon the first call, Fldid() loads the field table files and performs the required search. Thereafter, the files are kept loaded. Fldid() returns the field identifier corresponding to its argument on success, and returns BADFLDID on failure, with Ferror set to FBADNAME (Ferror32 is set for FML32).

To recover the data space used by the field tables loaded by Fldid(), the user may unload all of the files by a call to the Fnmid_unload() function.

The function Fname() acts in a fashion similar to Fldid(), but provides a mapping from a field identifier to a field name. It uses the same environment variable scheme for determining the field tables to be loaded, but constructs a separate set of mapping tables. On success, Fname() returns a pointer to a character string containing the name corresponding to the fldid argument. On failure, Fname() returns NULL.

Note: The pointer is valid only as long as the table remains loaded.

As with Fldid(), failure includes either the inability to find or open a field table (FFTOPEN), bad field table syntax (FFTSYNTAX), or a no-hit condition within the field tables (FBADFLD). The table space used by the mapping tables created by Fname() may be recovered by a call to the function Fidnm_unload().

Both mapping functions and other FML functions that use run-time mapping require FIELDTBLS and FLDTBLDIR to be set properly. Otherwise, default values are used. (See Chapter 3, "Setup," for the defaults.)

Field Header Files

The command mkfldhdr(1) (or mkfldhdr32) converts field tables, as described above, into header files suitable for processing by the C compiler. Each line of the generated header file is of the following form.

#define fname   fieldid

where fname is the name of the field, and fieldid is its field-ID. The field-ID has both the field type and field number encoded in it. The field number is an absolute number, that is, base plus rel-number. The resulting file is suitable for inclusion in a C program.

The header file need not be used if the run-time mapping functions are used as described in the next sub-section. The advantage of compile-time mapping of names to identifiers is speed and a decrease of data space requirements. The disadvantage is that changes made to field name/identifier mappings after, for instance, a service routine has been compiled will not be propagated to the service routine (that is, it will use the mappings it has already compiled).

mkfldhdr(1) translates each field-table specified in the FIELDTBLS environment variable to a corresponding header file, whose name is formed by concatenating a .h suffix to the field-table name. The resulting files are created, by default, in the current directory. The user may specify a creation directory to mkfldhdr(1) by specifying a -d option followed by the name of the directory in which you want the header files to reside. For example,

FLDTBLDIR=/project/fldtbls
FIELDTBLS=maskftbl,DBftbl,miscftbl
export FLDTBLDIR FIELDTBLS
mkfldhdr

FLDTBLDIR32=/project/fldtbls
FIELDTBLS32=maskftbl,DBftbl,miscftbl
export FLDTBLDIR32 FIELDTBLS32
mkfldhdr32

will produce the include files maskftbl.h, DBftbl.h and miscftbl.h in the current directory by processing ${FLDTBLDIR}/maskftbl, ${FLDTBLDIR}/DBftbl and ${FLDTBLDIR}/miscftbl. The command

mkfldhdr -d${FLDTBLDIR}

will process the sample input field-table files and produce the same output files, but will place them in the directory given by ${FLDTBLDIR}.

You may override the environment variables (or avoid setting them) when using mkfldhdr by specifying on the command line the names of the field tables to be converted (this does not apply to the run-time mapping functions). In this case, FLDTBLDIR is assumed to be the current directory and FIELDTBLS is assumed to be the list of parameters that the user specified on the command line. For example,

mkfldhdr myfields

will convert the field table file myfields to a field header file myfields.h, and place it in the current directory.

Mapping Fields to C Structures and COBOL Records

As mentioned in Chapter 2, "Overview," FML VIEWS is a mechanism that allows the exchange of data between fielded buffers and C structures or COBOL records. This capability is provided since it is usually more efficient to perform lengthy manipulations on C structures with C functions than on fielded buffers with FML functions. It also provides a way for a COBOL program to send and receive messages with a C program that handles FML fielded records.

This section discusses VIEWS and how to use it to provide fielded buffer/structure mappings. The figure below shows the various components of VIEWS and how they relate to one another. Each component is explained in the following sections.

Figure 4-1 Views

Viewfiles

Source viewfiles are standard text files (created through any standard text editor, such as vi) that contain one or more source view descriptions (the actual field-to-structure mappings).

The view compiler produces (among other things) object viewfiles containing the compiled object view descriptions. These object viewfiles can in turn be used as input to the view disassembler (viewdis or viewdis32), which translates the object view descriptions back into their source format (for verification or editing).

You create and edit the source view descriptions (or edit the output of viewdis) only; compiled view descriptions are not readable by an editor.

Besides the actual view description(s), viewfiles can contain comment lines, beginning with # or $. Blank lines and lines beginning with # are ignored by the view compiler, while lines beginning with $ are passed by the view compiler to any header files generated. This lets you pass C comments, what strings, etc., to C header files produced by the view compiler; they are not passed through to the COBOL copy files.

View Descriptions

Each source view description in a source viewfile consists of three parts:

A line beginning with the keyword VIEW (never with a 32 suffix), followed by the name of the view description; the name can have a maximum of 33 alphanumeric characters (including the underscore character); when used with tpalloc(3c), the maximum number of characters is 16.
A list of member descriptions.
A line beginning with the keyword END.

The first line of each view description must begin with the keyword VIEW followed by the name of the view description. A member description (or mapping entry) is a line with information about a member in the C structure or COBOL record. A line with the keyword END must be the last line in a view description.

Thus, a source view description has the general structure shown in Listing 4-2.

Listing 4-2 Source View Description

VIEW vname
  # type   cname   fbname   count   flag   size   null
  # ----   -----   ------   -----   ----   ----   ----
  --------------member descriptions-------------------
  .
  .
  .
  END

In Listing 4-2:

vname is the name of the view description, and should be a valid C identifier name, since it is also used as the name of a C structure; underscores are mapped automatically to dashes in the COBOL COPY file.
type is the type of the member, and is specified as one of the following: int, short, long, char, float, double, string, carray, dec_t; if type is `-', the type of the member is defaulted to the type of fbname.
cname is the identifier for the structure member, and should be a valid C identifier name, since it is the name of a C structure member; underscores are mapped automatically to dashes in the COBOL COPY file.
fbname is the name of the field in the fielded buffer; this name must appear in a field table file.
count is the number of elements to be allocated (that is, the maximum number of occurrences to be stored for this member); must be less than or equal to 65,535 for FML, and less than or equal to 2,147,483,647 for FML32.
flag is a list of options, separated by commas, or `-' meaning no options are set; see below for a discussion of flag options.
size is the size of the member if the type is string, carray, or dec_t; otherwise `-' should be specified, and the view compiler will compute the size. For string or carray, it must be less than or equal to 65,535 for FML and less than or equal to 2,147,483,647 for FML32. For the dec_t type, size is two numbers separated by a comma, the first being the number of bytes in the decimal value (it must be greater than 0 and less than 10) and the second being the number of decimal places to the right of the decimal point (it must be greater than 0 and less than two times the number of bytes minus one).
null is the user-specified null value or `-' to indicate the default null value for that field; see below for a discussion of null values.

viewc [-n] [-d viewdir] [-C] viewfile [viewfile ...]

where viewfile is the name of a source viewfile containing source view descriptions. You may specify one or more viewfiles on the command line.

If the -C option is specified, then one COBOL COPY file is created for each VIEW defined in the viewfile. These copy files are created in the current directory.

The -n option can be used when compiling a view description file for a C structure or COBOL record that does not map to an FML buffer.

By default, all views in viewfile are compiled and two or more files are created: an object viewfile (suffixed with ".V"), and a header file (suffixed with ".h") for each viewfile (see Figure 4-1).

The name of the object viewfile is viewfile.V. It is created in the current directory. The -d option can be used to specify an alternate directory. Header files are created in the current directory.

Note: Users of the BEA TUXEDO system Workstation feature in an MS-DOS environment will notice that the object viewfile is given a .vv suffix.

viewc C Header Files

Header files created by the view compiler (viewc) can be used in any C application programs to declare a C structure described by views. For example, the following view description

VIEW test
#TYPE   CNAME    FBNAME    COUNT    FLAG    SIZE     NULL
int     empid    EMPID       1        -       -      -1
float   salary   EMPPAY      1        -       -      0
long    phone    EMPPHONE    4        -       -      0
string  name     EMPNAME     1        -       32     "NO NAME"
END

produces a C header file that looks like this:

struct test {
 long    empid;                 /* null=-1 */
 float   salary;                /* null=0.000000 */
 long    phone[4];              /* null=0 */
 char    name[32];              /* null="NO NAME" */
};

COBOL COPY Files

COBOL COPY files created by the view compiler with the -C option can be used in any COBOL application programs to declare COBOL records described by views. For example, the COBOL COPY file for the previous view description will look like the following in the file TEST.cbl.

*       VIEWFILE: "test.v"
*       VIEWNAME: "test"
05 EMPID                  PIC S9(9) USAGE IS COMP-5.
05 SALARY                 USAGE IS COMP-1.
05 PHONE OCCURS 4 TIMES   PIC S9(9) USAGE IS COMP-5.
05 NAME                   PIC X(32).

Note that the COPY file name is automatically converted to upper case by the view compiler. The COPY file would be included in a COBOL program as follows.

01 MYREC COPY TEST.

The output in the resulting COPY files is more fully described in the BEA TUXEDO COBOL Guide.

View Disassembler

The view disassembler disassembles an object viewfile produced by the view compiler and displays view information in source viewfile format. In addition, it displays the offsets of structure members in the associated structure. It is usually used to verify the correctness of an object view description.

The command line looks like the following.

viewdis objviewfile...

By default, objviewfile in the current directory is disassembled. If this file is not found in the current directory, an error message is displayed. You can specify one or more view object files on the command line.

The output of viewdis looks similar to the original source view description(s), and can be edited and re-input to viewc. The order of the lines in the output of viewdis may be different from the order of the original source view description, but this does not affect the correctness of the object file.

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4. Field Definition and Use

Mapping Functions

Null Values

COBOL COPY Files