PLI Stream I/O

Stream I/O

1.       LIST Directed I/O

1.1 Advantages and Disadvantages

• Advantages of LIST directed I/O

-         It is easy to code and is a useful debugging tool

• Disadvantages of LIST directed I/O

-         In GET LIST the data needs to be separated by space or comma, and therefore more space is required to represent the input data.

-         In PUT LIST, data is presented at predefined tab position, and so we cannot format it to provide a more meaningful and pleasing report.

1.2 GET LIST

• For this type of input each data value in the stream must separated either by a blank or a comma.
• A Null field is indicated by the first non blank character or by two commas separated by an arbitrary number of blanks.
• e.g. If the statement is GET LIST (AB,C,D,E); the values keyed could be 100 90 80 70 90.

1.3 PUT LIST

-         Values of the data list items are converted to character representations and transmitted to the data stream.

-         A blank separates successive data values transmitted.

e.g. Lets consider the following:

PUT LIST (50,’ABC’,123,127);

PUT LIST(23,86,87);

Tab position     1     25    49    73    97    121

1st Line           50    ABC 123  127  23

2nd Line          86    87

-         Use SKIP(n) option to move the line feed to the nth line after the current line.

e.g. PUT SKIP LIST(123);

-         Use PAGE option cuases the data to be printed on the top of a new page.

e.g. PUT PAGE LIST(‘IGSI’);

-         Use LINE option to print the data on a specific line number.

e.g. PUT LINE(10) LIST (A,B);

2.       EDIT Directed I/O

2.1   Advantages

-         No Blanks are needed to separate the data items in the input stream

-         No punctuation marks are needed to indicate the type of input data.

Example: If we have to supply the following stream input:

       ‘435928’ ‘DAVID P. GOLDSMITH’ 10.55 41.3 103.21

Only 37 positions are needed if edit directed input as compared to 47 positions for list directed input.

2.2   STRING Option

l         Instead of getting data form an external device(a file) the data can also be read from a character string. e.g.

       GET STRING(NAME) EDIT(FIRST,MIDDLE,LAST)(A(15),A(1),A(20));

l         It can be used to effect character to arithmetic and arithmetic to character string conversion.

       DCL EMP# CHAR(7);

DCL HOURS FIXED DEC(3,1);

DCL NAME CHAR(20);

       DCL RATE FIXED DEC(4,2);

DCL RECORD CHAR(80);

       PUT STRING (RECORD) EDIT(NAME,EMP#,HOURS*RATE)(A(20),A(7),F(7,2));

l         Sometimes records of different formats appear in the same file where each record contains a code that identifies the particular format;

       GET EDIT (INFO)(A(80));

       SELECT(SUBSTR(INFO,1,1));

        WHEN(‘1’)

              GET  STRING(INFO)

EDIT(CUST#,DATE,AMT)(X(1),A(6),X(3),A(6),X(1),F(7,2));

        WHEN(‘2’)

GET  STRING(INFO)         EDIT(CUST#,AMT,INVOICE#)(X(1),A(6),X(1),F(7,2),X(1),A(8));

        OTHERWISE

              CALL ERROR_IN_INPUT;

       END;

2.3 Conversion of external data to internal data format

Arithmetic data items have the format F (fixed point) or E (floating point). Following data types may be input or output using the F, E or P format items.

• FIXED BINARY
• FIXED DECIMAL
• FLOAT BINARY
• FLOAT DECIMAL

e.g. DCL HOURS FIXED DEC(3);

   GET EDIT(HOURS) (A(3));  /* provided HOURS contain only the digits 0 through 9 */

2.4   Control Items

l         COLUMN:

l         LINE:

l         PAGE:

l         SKIP:

3         DATA Directed I/O

3.1 Data directed input:

l         Each item in the input is in the form of an assignment statement that specifies both the value and the variable to which it is to be assigned.

l         Statements are separated by blanks or commas.

l         Semicolon ends each group of items to be accessed by a single GET statement.

e.g. A= 12.3,B=57,C=‘ABCDEF’,D=‘1110’B;

GET DATA(A,B,C,D);

l         Maximum number of elements permitted in a list = 320;

l         Data list may include the name that do not appear in the list, but the vice versa is not true.

l         If the data list is an array, subscripted references to that array may appear in the stream. e.g.

DCL TABEL(50) FIXED DEC(5,2);

GET DATA (TABLE);

Input stream could be:    TABLE(3)=7.95, TABLE(4)=8.43,TABLE(7) = 50;

3.2   DATA DIRECTED OUTPUT:

l         Each data item is placed in the stream in the form of assignment statements.

l         Last item output is followed by a semicolon.

l         Leading zeros of arithmetic data are suppressed.

e.g. DCL A FIXED DEC(5) INIT(0);

       DCL B FIXED DEC(5) INIT(0);

       DCL C FIXED BIN(15) INIT(175);

       PUT DATA(A,B,C);

Tab position                     1        25         49

Output would look like:        A=0       B=0       C=175;