On OpenVMS, Compaq COBOL and Compaq COBOL for OpenVMS VAX exhibit different behavior when calling a subprogram installed as a shareable image. With Compaq COBOL, the program name you specify in a CALL statement can be either a literal or a data-name. (The same is true for the CANCEL statement.) With Compaq COBOL for OpenVMS VAX, the program name you specify in a CALL (or CANCEL) statement must be a literal. In addition, Compaq COBOL for OpenVMS VAX programs installed as shareable images cannot contain external files. (See Chapter 1 and OpenVMS Linker Utility Manual for more information about shareable images.) <>

On Windows NT and Tru64 UNIX systems, Compaq COBOL exhibits behavior more like Compaq COBOL for OpenVMS VAX with regard to shared objects. (Shared objects are the Windows NT and Tru64 UNIX equivalent to OpenVMS shared images.) For more information, see Chapter 12, Interprogram Communication. <>

B.4.11 Sharing Common Blocks (OpenVMS)

On OpenVMS, to prevent problems when you link a Compaq COBOL program and want to share a common block between processes, you should set the PSECT attribute to SHR (the defaults are: SHR on OpenVMS Alpha systems, NOSHR on OpenVMS VAX systems). Also, you should add a SYMBOL_VECTOR to the linker options file of the shareable image, as follows:

SYMBOL_VECTOR = (psect-name = PSECT)

For more information, see the OpenVMS Linker Utility Manual. <>

B.4.12 Arithmetic Operations

Several arithmetic operations differ in behavior between Compaq COBOL and Compaq COBOL for OpenVMS VAX, depending upon your platform:

• Results of numeric and integer Intrinsic Functions may differ from Compaq COBOL for OpenVMS VAX or may be formatted differently by a DISPLAY statement.
• OpenVMS VAX and OpenVMS Alpha handle COMP-2 items differently. As a result, DISPLAY of a USAGE COMP-2 data item low order digits may be different from the low order digits of the data item from the DISPLAY with Compaq COBOL for OpenVMS VAX on OpenVMS VAX.
• Compaq COBOL issues the ALL_LOST (all digits lost) warning diagnostic in different cases than Compaq COBOL for OpenVMS VAX.
• When overflow occurs in an arithmetic statement without a SIZE ERROR phrase and native arithmetic is used, the results are undefined. Compaq COBOL for OpenVMS VAX often returns the low order digits of the true result in such cases; Compaq COBOL does not. When standard arithmetic is used, the results are unaltered.
• The precision of intermediate results is different between Compaq COBOL for OpenVMS VAX and Compaq COBOL. This is most noticeable in COMPUTE operations involving a divide. If you need a specific precision for an intermediate result, you should use a temporary variable with the desired precision. For example:

  COMPUTE D = (A / B) / C.

  ...could be written as

  COMPUTE TMP1 = A / B. COMPUTE D = TMP1 / C.

  
  The precision to be used for the calculation A / B would be established by your declaration of TMP1.

• On Windows NT and Tru64 UNIX, the VAX floating point data types, F_FLOAT, D_FLOAT, and G_FLOAT are not supported; whereas, on OpenVMS Alpha systems, F_FLOAT and D_FLOAT are the defaults for floating point. This difference potentially affects reading data files with COMP-1 and COMP-2 keys built on OpenVMS Alpha systems. Also, any programs that check for specific floating values rather than ranges of values may be impacted.
• The results of numeric comparisons with Compaq COBOL for OpenVMS VAX and Compaq COBOL are undefined with invalid decimal data. Compaq COBOL includes the /CHECK=DECIMAL and -check decimal features to do a more complete analysis of invalid decimal data. These options can be particularly helpful when you are migrating programs to Compaq COBOL.
• There is some inevitable incompatibility in results of arithmetic operations involving large intermediate values, between Compaq COBOL and Compaq COBOL for OpenVMS VAX. In Compaq COBOL, to minimize the differences, you can use the /MATH_INTERMEDIATE=CIT3 qualifier (or -math_intermediate cit3 ). With it, use the /ARITHMETIC=NATIVE qualifier (or -arithmetic native ), which is the default. (Specifying /ARITHMETIC=STANDARD would force /MATH_INTERMEDIATE=CIT4.)
  CIT3 gives improved compatibility between Compaq COBOL and Compaq COBOL for OpenVMS VAX. Even with CIT3, however, there are differences:
  • Invalid decimal data
    In Compaq COBOL, invalid decimal data detection takes place before any possible conversion to CIT3. CIT3 operations on data items containing invalid decimal data will get results possibly different from those with Compaq COBOL for OpenVMS VAX.
  • Floating-point data items
    In Compaq COBOL, expressions involving COMP-1 or COMP-2 data items are converted to G_floating (on OpenVMS Alpha) or T_floating before conversion to CIT3. CIT3 operations involving D_floating (on OpenVMS Alpha) data items, in particular, will get different results from Compaq COBOL for OpenVMS VAX.
  • Undefined results
    If an abnormal condition arises during a CIT3 operation, for example, INTEXPOVE (intermediate exponent overflow), and the program continues, and it is not an arithmetic statement with an ON SIZE ERROR clause, then the values that are stored in destination items will be undefined. Compaq COBOL and Compaq COBOL for OpenVMS VAX are highly likely to get different undefined results in such cases.
  • STANDARD dependency
    The Compaq COBOL for OpenVMS VAX /STANDARD qualifier has an effect on when arithmetic expression analysis switches to one of the CIT forms. When you specify /STANDARD=V3 (-std v3), CIT is used when more than 18 digit intermediate results are needed. With /STANDARD=85 (-std 85), CIT is used when more than 31 digit intermediate results are needed. The Compaq COBOL implementation on Alpha is compatible with Compaq COBOL for OpenVMS VAX with /STANDARD=85.
  • Special contexts
    The CIT3 implementation does not provide support equivalent to the Compaq COBOL for OpenVMS VAX behavior for intrinsic functions MEDIAN, NUMVAL, and NUMVAL-C.
    See Section 2.7.1 in this manual, and the Compaq COBOL Reference Manual for more information on the /MATH_INTERMEDIATE and /ARITHMETIC qualifiers.

Certain Compaq COBOL features have unique behaviors, depending upon which of these operating systems you are using, and sometimes these differences differ from release to release. You should refer to the Release Notes to get the most recent information about these differences. The next few sections describe distinct differences in feature implementation and behavior.

B.5.1 REWRITE

A REWRITE operation for an ISAM file is dependent on whether the DUPLICATES clause for the primary key is specified. There is an ambiguity when DUPLICATES is specified in one way at the time a file is created, and another way when it is reopened (a program should use the same declarations). Both Compaq COBOL for OpenVMS VAX and Compaq COBOL for OpenVMS Alpha use the specification of the current program. So, if DUPLICATES was specified for the primary key when a file was created, but not when reopened by the current program, the behavior will be as if DUPLICATES were not allowed.

Compaq COBOL on Windows NT and on Tru64 UNIX issues a severe run-time error if there is a mismatch, unless relax key checking (the -rkc flag) is specified, in which case the behavior is inconsistent. In many cases, you will get the behavior of the specification when the file was created, but you should not rely on this.

B.5.2 File Sharing and Record Locking

With Compaq COBOL on Windows NT and on Tru64 UNIX, certain file-sharing and record-locking operations may behave differently from the same operations on Compaq COBOL on OpenVMS Alpha. Compaq COBOL on Windows NT and Tru64 UNIX issues warning diagnostics where applicable.

• File sharing for sequential and relative files on all systems remains essentially the same. One notable exception is REGARDLESS, which is not supported on Windows NT systems.
• File sharing for indexed files has the following limitation: The OPEN statement ALLOWING READERS phrase is minimally supported for indexed files on Windows NT and Tru64 UNIX systems. Using the ALLOWING READERS phrase for indexed files is not recommended.
• File-sharing protocols for all file organizations are in effect for Windows NT and Tru64 UNIX systems for the OPEN statement in OUTPUT mode, which is similar to EXTEND and I-O modes. On Windows NT and Tru64 UNIX systems, access is denied or granted depending on the file lock requested and the file lock held (with the exception of the READERS support noted previously.) On OpenVMS Alpha, a new version of the file is always created.
• Manual record locking for files with the indexed organization has the following limitations:
  • For the READ and START statements, the REGARDLESS phrase is not fully supported. The read or start operation is performed but the soft record lock status is not returned.
  • The START statement does not detect or acquire a record lock.
  • The READ statement with the ALLOWING READERS phrase is not supported. It is treated as NO OTHERS if the file is opened in I-O mode or it is treated as ALL if the file is opened in INPUT mode.
  • The REWRITE and WRITE statements do not retain record locks.
  • The (current) RECORD phrase is not supported for the UNLOCK statement. The ALL RECORDS phrase is assumed for all UNLOCK statements.

If a VFC file is created on OpenVMS Alpha and then read on Windows NT or Tru64 UNIX, the data record will be returned with the 2-byte control string in the data record when it is read.

The workaround is to convert the file to a non-VFC format on OpenVMS Alpha. VFC files are created on OpenVMS Alpha by Compaq COBOL for OpenVMS VAX and Compaq COBOL for the following:

LINAGE
REPORT WRITER
SEQUENTIAL EXTERNAL/GLOBAL
Output with WRITE ADVANCING

Compaq COBOL on Tru64 UNIX and Windows NT systems provides limited file attribute checking. No file attribute checking is performed for sequential and relative files. For indexed files, Compaq COBOL verifies that the following file attributes match what is specified in the application:

• Number of keys
• Size and position (within the record structure) of each key
• Whether or not duplicates are allowed for each key

If these attributes are not matching, the file will not be opened and a fatal runtime error will occur (or Declaratives will be invoked, if applicable).

However, with the relax key checking option selected Compaq COBOL will allow you to open a file which specifies fewer keys than were specified when the file was originally created. This option will provide correct results only in those cases where the unspecified keys are USAGE DISPLAY (PIC X). Also, -rkc allows you to open a file which specifies DUPLICATES for a key in a way differently from the specification given when the file was created.

There is an additional check in creating an indexed file: unless relax key checking is specified, you may not have two keys that are identical except for whether DUPLICATES are allowed. If this restriction is violated, there will be an explicit run-time error message and those operations that are affected by DUPLICATES may give unexpected results.

B.5.5 Indexed Files

Compaq COBOL on Tru64 UNIX and Windows NT treats indexed files differently from the way they are treated by both Compaq COBOL on OpenVMS Alpha and Compaq COBOL for OpenVMS VAX on OpenVMS Alpha. Specifically:

• For an indexed file, the run-time system creates two files on the disk: one file with the dat extension, and the other file with the idx extension. Additionally, on Windows NT a file with the lck extension is created.
• If you try to open an indexed file as a sequential file, the key part of any record other than a character key will be different. The reason is that the keys in a record are translated to a file format on disk.
• When you open an existing indexed file, the RTL checks its key structure and returns a severe error if there is a serious mismatch.
  On Windows NT and Tru64 UNIX, this RTL check does not detect some differences that would be detected on an OpenVMS Alpha system, because all but signed 16- and 32-bit integers are mapped onto character strings. For example, if you write an indexed file using a key described as an unsigned 32-bit integer, the character string you will read is the integer with its bytes reversed. On an OpenVMS Alpha system, by contrast, you receive a severe error when you try to open a file with the incompatible key.

Compaq COBOL on Windows NT and Tru64 UNIX does not support RMS Special Registers. If you include them, you may receive the following general diagnostic message when you attempt to compile the program:

cobol: Severe: ...Undefined name

B.5.7 Time and Fractional Seconds

Fractions of seconds are not handled by the Compaq COBOL runtime library on Windows NT. The value zero is returned for those parts which cannot be determined. This impacts the following:

ACCEPT FROM TIME
FUNCTION CURRENT-DATE
FUNCTION WHEN-COMPILED <>

Files created by different programming languages may require special processing because of language and character set incompatibilities. The most common incompatibilities are data types and data record formats. You should be aware of the following:

• Print-controlled files that are created on Windows NT or the Tru64 UNIX operating system cannot be used as VFC files on the OpenVMS Alpha operating system.
• VFC files cannot be used on Windows NT or on the Tru64 UNIX operating system.
• On Windows NT and Tru64 UNIX, to read a file with variable-length records, you must describe the file as such in the program (use RECORD IS VARYING). On OpenVMS Alpha, you can read a file with variable-length records by using a file description for fixed-length records.
• On OpenVMS Alpha, a file with fixed-length records can be described in a COBOL program with an FD specifying a length shorter than the file record length. On input, the extra data in each record is ignored on OpenVMS Alpha. On Windows NT and Tru64 UNIX, the length specified for the FD must match the actual length of the records in the file; you must not use RECORD IS VARYING to read a file with fixed-length records.
• On OpenVMS Alpha, an existing ORGANIZATION INDEXED file cannot be read with an FD specifying ORGANIZATION SEQUENTIAL. To read the file on Windows NT or Tru64 UNIX sequentially, use ORGANIZATION INDEXED, ACCESS SEQUENTIAL (or DYNAMIC), and READ NEXT.

Data Type Differences

Data types vary by programming language and by utilities. For example, Compaq Fortran does not support the packed-decimal data type and, therefore, cannot easily use PACKED-DECIMAL data in COBOL files.

You can use the following techniques to overcome data type incompatibilities:

• Use the NATIVE character set, which uses ASCII representation, for all data in files intended for use across languages.
• If your requirements include processing non-ASCII data, you can specify a character set in: (1) the SPECIAL-NAMES paragraph of the Environment Division, along with (2) the CODE-SET clause in the SELECT statement. Except for NATIVE, you must specify all character sets in the SPECIAL-NAMES paragraph.
• Use common numeric data types (numeric data types that remain constant across the application).

In the following example, the input file is written in EBCDIC. This creates a file that would be difficult to handle in most languages other than COBOL on the OpenVMS Alpha operating system.

ENVIRONMENT DIVISION. CONFIGURATION SECTION. SPECIAL-NAMES. ALPHABET FOREIGN-CODE IS EBCDIC. INPUT-OUTPUT SECTION. FILE-CONTROL. SELECT INPUT-FILE ASSIGN TO "INPFIL" CODE-SET IS FOREIGN-CODE. . . .

B.7 LIB$INITIALIZE Interaction Between C and COBOL

If you use LIB$INITIALIZE when the main program is written in Compaq COBOL and the initialize routine is written in Compaq C, the initialize routine will not be called. If you are using Compaq COBOL for OpenVMS VAX on OpenVMS VAX Version 7.1, however, the routine will be called; also, it will be called if your main program is in C or in BASIC rather than COBOL, so this can be a practical workaround.

The problem is due to the quadword alignment with which C creates the LIB$INITIALIZE psect. The LIB$INITIALIZE psect requires longword alignment. The programmer can explicitly specify longword alignment on the extern_model pragma to avoid the problem.

B.8 Reserved Words

Depending on the use of the /RESERVED_WORDS qualifier or flag, there are a number of additional reserved words in Compaq COBOL that are not reserved in Compaq COBOL for OpenVMS VAX. See the appendix on reserved words in the Compaq COBOL Reference Manual for complete information.

B.9 Debugger Support Differences

Compaq COBOL debugger support differs in several ways from Compaq COBOL for OpenVMS VAX:

• Compaq COBOL issues the following informational message when the /DEBUG qualifier is used on the COBOL command line with the default optimization in effect:

  %COBOL-I-DEBUGOPT, /NOOPTIMIZE is recommended with /DEBUG

  
  You receive this message if you specify nothing about optimization when you specify /DEBUG. (/OPTIMIZE is the default for the compiler.) Unlike other informational messages, which are turned off by default, this message is always allowed through by the Compaq COBOL compiler, even if /WARN=NOINFO is in effect. To turn the message off, use any form of the qualifier /[NO]OPTIMIZE on the COBOL command line (for example, /NOOPTIMIZE or /OPTIMIZE or /OPTIMIZE=LEVEL=x).

• Compaq COBOL for OpenVMS VAX does not have the /OPTIMIZE qualifier.
• With Compaq COBOL, unlike Compaq COBOL for OpenVMS VAX, the debugger sometimes changes underscores to hyphens and hyphens to underscores in variable names.
  This difference from Compaq COBOL for OpenVMS VAX can help you debug a program. Because these messages are informational, the compiler produces an object file, which you can link and execute. However, the messages may point out otherwise undetected logic errors, as the structure of the program is probably not what you intended.

Compaq COBOL does not support the DECset/LSE Program Design Facility, the /DESIGN qualifier, design comments, or pseudocode placeholders.

B.11 DBMS Support

On OpenVMS, Compaq COBOL support for Oracle DBMS has some differences depending on your platform (specifically, whether you are developing programs with Compaq COBOL on OpenVMS Alpha or with Compaq COBOL for OpenVMS VAX). <>

B.11.1 Compiling on Tru64 UNIX and Windows NT

In Compaq COBOL for Windows NT or Tru64 UNIX, Oracle DBMS sub-schema access (DML for Oracle DBMS) is not supported. Attempting to compile a program containing any Oracle DBMS syntax results in the following diagnostic message:

cobol: Severe: ...DBMS Data Manipulation Language is not supported

Oracle DBMS syntax includes the following language elements: SUB-SCHEMA, DB, DB-EXCEPTION, LD, COMMIT, CONNECT, ERASE, FETCH, FIND, FREE, GET, KEEP, MODIFY, READY, RECONNECT, ROLLBACK, STORE, RETAINING, WHERE, EMPTY, MEMBER, OWNER, and TENANT.

You may also receive the following general diagnostic message when you attempt to compile a program (on Tru64 UNIX) that contains variables defined in your Oracle DBMS sub-schema:

cobol: Severe: ...Undefined name

B.11.2 Multistream DBMS DML

With Compaq COBOL, when you use multistream Oracle DBMS DML, you must access different schemas or streams from separate source files.