Kednos PL/I for OpenVMS Systems
Reference Manual
Previous Contents Index

2.2.49 STATIC Attribute

The STATIC attribute specifies the way that PL/I is to allocate storage for a variable. The format of the STATIC attribute is: 

STATIC

The STATIC attribute is implied by the EXTERNAL attribute. For more information on STATIC and on other storage-class attributes, see Chapter 5.

Restriction

The STATIC attribute directly conflicts with the BASED, CONTROLLED, DEFINED, and parameter attributes. The STATIC attribute cannot be applied to members of structures, parameters, or descriptions in an ENTRY or RETURNS attribute.

2.2.50 STREAM Attribute

The STREAM file description attribute indicates that the file consists of ASCII characters and that it will be processed using GET and PUT statements. The format of the STREAM attribute is: 

STREAM

The STREAM attribute is implied by the PRINT attribute. It is also supplied by default for a file that is implicitly opened with a GET or PUT statement.

Specify the STREAM attribute in a DECLARE statement for a file identifier or in the OPEN statement that opens the file.

Restriction

The STREAM attribute directly conflicts with the RECORD, KEYED, DIRECT, SEQUENTIAL, and UPDATE attributes.

2.2.51 STRUCTURE Attribute

You can optionally specify the STRUCTURE attribute in the declaration of a structure. The format of the STRUCTURE attribute is: 

STRUCTURE

2.2.52 TYPE Attribute

The TYPE attribute copies the declarations contained within the type declaration to the variable to which it is applied. The format of the TYPE attribute is: 

level-number identifier [attributes] TYPE reference

level-number

The level number to which the declarations in the reference are copied.

identifier

The variable to which the declarations in the reference are to be copied. The identifier must be preceded by a level number.

attributes

Storage class or dimensions appropriate for the level number. You can specify a storage class and dimensions with a major structure, or you can specify dimensions with a minor structure.

reference

The name of a type declaration that is known in the current block.

The TYPE attribute causes the declaration of its reference to be copied, but not the name, storage class, or dimensioning (if any) of the reference. The exception to this rule is that the UNION attribute is propagated in a TYPE declaration. While logical structuring is copied, the level numbers themselves are not copied.

You can use the TYPE attribute on a declaration already containing the TYPE attribute.

Restrictions

A TYPE definition cannot be:

2.2.53 TRUNCATE Attribute

The TRUNCATE attribute is used in the declaration of a formal parameter to indicate that the actual parameter list can be truncated at the point where this argument should occur. The format of the TRUNCATE attribute is: 

TRUNCATE

When the actual call is made, the actual parameter list can stop at the parameter before the one declared with the TRUNCATE attribute. It is possible to pass an actual parameter in a position with the TRUNCATE attribute. Note that in this case, all remaining parameters must also be specified unless they have the TRUNCATE attribute.

A subtle difference between trailing formal parameters for which the TRUNCATE attribute is specified and trailing formal parameters for which the OPTIONAL attribute is specified is that when no actual parameters are specified, the compiler will automatically fill out the minimum argument vector length requires (such as by certain VMS system services) in the OPTIONAL case, but not if only TRUNCATE is specified.

Example 


DCL E ENTRY (FIXED,FIXED TRUNCATE,FIXED); 
CALL E(1); 
CALL E(1,2,3);

The following call, however, will be invalid: 


CALL E(1,2);

This call is invalid because the second parameter has the TRUNCATE attribute, so the third parameter must be specified.

2.2.54 UNALIGNED Attribute

The UNALIGNED attribute is used in conjunction with the BIT attribute to specify that a bit-string variable should not be aligned on a byte boundary. Because UNALIGNED is the default for bit strings, it need not be specified. The format of the UNALIGNED attribute is:

You can use the UNALIGNED attribute in the declaration of character strings. All character strings are aligned on byte boundaries; therefore, the UNALIGNED attribute has no effect on the actual storage of a character string.

Restriction

The UNALIGNED attribute conflicts with all data-type attributes other than BIT and CHARACTER.

2.2.55 UNION Attribute

The UNION attribute, which can be used only in conjunction with a level number in a structure declaration, signifies that all immediate members of the major or minor structure so designated occupy the same storage. Immediate members are those members having a level number 1 higher than the major or minor structure with the UNION attribute. For example, if the UNION attribute were associated with level n, then all members or minor structures at level n+1 up to the next member at level n would be immediate members and would occupy the same storage. The format for the UNION attribute is: 

level-number identifier [storage-class] UNION

level-number

The level number of the variable with which the declarations in the reference share storage.

identifier

Names the variable with which the declarations in the reference share storage. A variable declared with the UNION attribute must be a major or minor structure.

storage-class

The storage class specified for the structure. You can specify the storage class only on level 1.

2.2.56 UPDATE Attribute

The UPDATE attribute is a file description attribute indicating that the associated file is to be used for both input and output. You can apply the UPDATE attribute to relative files, indexed files, and sequential disk files with fixed-length records. The format of the UPDATE attribute is: 

UPDATE

Specify the UPDATE attribute on a DECLARE statement for a file constant or on an OPEN statement to access the file for update. The UPDATE attribute implies the RECORD attribute.

For a description of the attributes that are applied to files, see Section 9.1.3.3.

Restriction

The UPDATE attribute directly conflicts with the INPUT, OUTPUT, STREAM, and PRINT attributes and with any data-type attribute other than FILE.

2.2.57 VALUE Attribute

The VALUE attribute is provided for passing parameters by value rather than by reference, or it can be used to specify a global constant value. The format of the VALUE attribute is:

The VALUE attribute serves two purposes:

The VALUE attribute, when specified with the BIT attribute, implies the ALIGNED attribute.

2.2.58 VARIABLE Attribute

The VARIABLE attribute indicates that the associated identifier is a variable. VARIABLE is implied by all computational data-type attributes and by all noncomputational attributes except FILE and ENTRY. The format of the VARIABLE attribute is: 

VARIABLE

If you specify the FILE or ENTRY attribute in a DECLARE statement without the VARIABLE attribute, the defined object is assumed to be a file or entry constant.

The VARIABLE attribute is implied by the LABEL attribute. You can declare label constants only by using the label identifier in the program; you cannot define a label constant in a DECLARE statement.

Restriction

The VARIABLE attribute is not valid in a returns descriptor or in a parameter descriptor.

2.2.59 VARYING Attribute

The VARYING attribute indicates that a character-string variable does not have a fixed length, but that its length changes according to its current value. The format of the VARYING attribute is:

You must specify a length attribute in conjunction with VARYING by giving the maximum length allowed for the variable. The current length is stored with the value and can be determined at any time with the LENGTH built-in function. If you need to determine the maximum declared length of a varying- length character string, use the MAXLENGTH built-in function.

The value of an uninitialized CHARACTER VARYING variable is undefined.

Special rules apply to reading and writing record files into and from variables that have the VARYING attribute. See the Kednos PL/I for OpenVMS Systems User Manual.

Restriction

The VARYING attribute directly conflicts with any data-type attribute other than CHARACTER.

Examples 


DECLARE STRING CHARACTER(80) VARYING;

A variable named STRING is declared as a varying-length character string with a maximum length of 80 characters. 


S: PROCEDURE OPTIONS(MAIN); 
DECLARE STRING CHARACTER(80) VARYING; 
    STRING = 'PIE'; 
    PUT LIST (LENGTH(STRING)); 
    PUT LIST (MAXLENGTH(STRING)); 
    PUT LIST (SIZE(STRING)); 
END;

The value returned by the built-in function LENGTH is 3, the length of the current value of the string. The value returned by the built-in function MAXLENGTH is 80, the maximum declared length. The value returned by the built-in function SIZE is 82, the maximum declared length plus two (for the two bytes that hold the value of the current length).

Chapter 3
Data Types

All programs process data items. Data items can be constants or variables. A constant data item has a value that does not change during program execution; a variable data item can represent different values.

A data item has an associated type that you can specify as an attribute or collection of attributes in a declaration. Unlike other languages that often have a distinction between data types and data attributes, a PL/I data type is entirely defined by the data attributes given to a data item identifier. The data type that you select determines the operations that you can perform on data items and how they are stored.

The rest of this chapter describes data types in more detail.

3.1 Summary of Data Types

PL/I supports the following computational data types:

PL/I also supports the following noncomputational data types and attributes:

You can place each of these data types in aggregate structures or arrays to form new data types. See Chapter 4 for more information.

3.1.1 Declarations

All names referenced in a PL/I program must be declared explicitly, with the exception of entry-point names, statement labels, built-in functions, and the default file constants SYSIN and SYSPRINT. You declare a name and its data type attributes in a DECLARE statement. For example: 


DECLARE AVERAGE FIXED DECIMAL; 
DECLARE NAME CHARACTER (20);

The keywords DECIMAL, FIXED, and CHARACTER describe characteristics, or attributes, of the variables AVERAGE and NAME.

3.1.2 Default Attributes

It is not always necessary to define all the characteristics, or attributes, of a variable; the PL/I compiler makes assumptions about attributes that are not explicitly defined. For example: 


DECLARE NUMBER FIXED;

The default FIXED attribute implies the attributes BINARY(31,0). Thus, the variable NUMBER has the attributes FIXED BINARY(31,0).

Table 3-1 shows the default attributes implied by each computational data attribute.

Table 3-1 Implied Attributes for Computational Data
Specified Implied
FIXED BINARY(31,0)
BINARY FIXED(31,0)
FIXED BINARY (31,0)
FLOAT BINARY(24)
FLOAT BINARY (24)
DECIMAL FIXED(10,0)
FIXED DECIMAL (10,0)
FIXED DECIMAL(p) (p,0)
FLOAT DECIMAL (7)
BIT [ALIGNED] (1)
CHARACTER [VARYING] (1)
PICTURE 'picture'  

3.1.2.1 Attributes of Constants

Constants have attributes implied by the characters used to specify them. The following list describes the expression of constants and their attributes:

Note that PL/I has no constants with the attributes FIXED BINARY, FLOAT BINARY, or PICTURE. However, this presents no problems in programming because you can assign constants of any computational type to variables of any computational type and they are converted automatically to the target type.

You usually give values to binary variables by assigning decimal constants to them. For example: 


I = 1;
This converts the decimal integer 1 and assigns the converted value to a fixed-point binary variable I. Consider the following example: 


F = 1.333E-12;
This converts the floating-point decimal constant 1.333E-12 and assigns the converted value to a floating-point binary variable F.

Picture variables are usually given values by assigning fixed-point decimal constants. For example: 


PAY_PIC = 123.44;
This assigns the fixed-point decimal value 123.44 to a picture variable PAY_PIC. The value of PAY_PIC is a pictured value, which is stored internally as a character string containing the characters 1, 2, 3, 4, and 4, along with any special formatting symbols defined for PAY_PIC.

3.1.2.2 Arithmetic Operands

The implied data types of constants are important primarily because of PL/I's rules for converting operands in an arithmetic operation. (Bit-string and character-string operations must have bit- and character-string operands, respectively.) All operations, including arithmetic operations, must be performed in a single data type, and automatic conversions are performed on arithmetic operands to make this possible. For example: 


DECLARE X FLOAT DECIMAL (49); 
X = X + 1.3;

In this example, the fixed-point decimal constant 1.3 is converted to floating-point decimal before the addition is performed. The rules for operand conversion are discussed in detail in Section 6.4.2.

For information about arithmetic operators, operands, and data conversions, see Chapter 6.

3.1.3 Compatible Data Types

In PL/I, the notion of compatible data types is used in the rules for passing arguments by reference and for based, controlled, defined, or external variables. For two nonstructure variables to have compatible data types, the following attributes must agree. That is, if one variable has the attribute, the other variable must also have it after the application of default rules.
ALIGNED DIMENSION OFFSET
AREA ENTRY picture
array bounds FILE PICTURE
BINARY FIXED POINTER
BIT FLOAT precision
CHARACTER LABEL PRECISION
DECIMAL length VARYING

Two pictured variables must have identical pictures after the expansion of iteration factors.

In addition, the following values must be equal:

Two structure variables have compatible data types if they have the same number of immediate members, and if corresponding members have compatible data types.

In general, you can specify string lengths, area sizes, and array bounds with expressions or with asterisks. The values used to determine whether two variables have compatible data types are obtained as follows:

Consider the following example: 


/* Example of extent determination */ 
 
DATAT: PROCEDURE (PTR1); 
 
DECLARE N FIXED, S CHARACTER(N) BASED(PTR1); 
DECLARE PTR1 POINTER; 
 
N = 10; 
 
CALL P(S); 
 
P: PROCEDURE(A); 
 
     DECLARE A CHARACTER(*), B CHARACTER(N); 
     N = 20; 
     PUT LIST(LENGTH(A),LENGTH(B),LENGTH(S)); 
     END P; 
 
END DATAT;

The PUT statement writes out: 


10     10     20

The assignment to N inside the procedure P affects the extent of S, but not the extents of A or B, which were frozen when P was invoked.

Previous Next Contents Index