15.1.15 PSECT Directive

The PSECT directive modifies several characteristics of a common block. It takes the following form:

 cDEC$ PSECT /common-name/ a [,a] . . .
Is one of the following: C (or c), !, or * (see Section 15.1.1).
Is the name of the common block. The slashes ( / ) are required.
Is one of the following keywords:

  • ALIGN=val or ALIGN=keyword

    Specifies alignment for the common block.

    The val is a constant ranging from 0 through 16 on VMS systems, 0 through 6 on Windows NT and Windows 9* systems, and 0 through 4 on Tru64 UNIX systems. The specified number is interpreted as a power of 2. The value of the expression is the alignment in bytes.

    The keyword is one of the following:

    Keyword  Equivalent to val 
    BYTE  0 
    WORD  1 
    LONG  2 
    QUAD  3 
    OCTA  4 
    PAGE (VMS only) [1] 16  

    [1] On Tru64 UNIX, Windows NT and Windows 9* systems, this keyword produces an error.

  • GBL (VMS only)

    Specifies global scope.

  • LCL (VMS only)

    Specifies local scope. This keyword is opposite to GBL and cannot appear with it.


    Controls whether the compiler pads the size of common blocks to ensure compatibility when the common block program section (psect) is shared by code created by other Compaq compilers.

    When a program section generated by a Fortran common block is overlaid with a program section consisting of a C structure, linker error messages can occur. This is because the sizes of the program sections are inconsistent; the C structure is padded, but the Fortran common block is not.

    Specifying MULTILANGUAGE ensures that Compaq Fortran follows a consistent program section size allocation scheme that works with DEC C program sections shared across multiple images. Program sections shared in a single image do not have a problem.

    You can use a compiler option to specify MULTILANGUAGE for all common blocks in a module.

  • [NO]SHR (VMS only)

    Determines whether the contents of a common block can be shared by more than one process.

  • [NO]WRT (VMS only)

    Determines whether the contents of a common block can be modified during program execution.

Rules and Behavior

Global or local scope is significant for an image that has more than one cluster. Program sections with the same name that are from different modules in different clusters are placed in separate clusters if local scope is in effect. They are placed in the same cluster if global scope is in effect.

If one program unit changes one or more characteristics of a common block, all other units that reference that common block must also change those characteristics in the same way.

Default characteristics apply if you do not modify them with a PSECT directive. Table 14-1 lists the default characteristics of common blocks and how they can be modified by PSECT.

Table 15-1 Common Block Defaults and PSECT Modification

Default Characteristics  PSECT Modification 
Relocatable  None 
Overlaid  None 
Global Scope  Global or local scope 
Not executable  None 
Not multilanguage  Multilanguage or not multilanguage 
Writable  Writable or not writable 
Readable  None 
No protection  None 
On Alpha processors: 
Not shareable  Shareable or not shareable 
Position dependent  None 
Octaword alignment[1] (4)  VMS: 0 through 16 [2] 
Windows NT: 0 through 6 [3]
Tru64 UNIX: 0 through 4 [3]
On Intel processors: 
Shareable  Shareable or not shareable 
Position independent  None 
Octaword alignment[1] (4)  0 through 6 [3] 

[1] An address that is an integral multiple of 16.
[2] Or keywords BYTE through PAGE.
[3] Or keywords BYTE through OCTA.

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