Using PRINT files with stream I/O
Both the operating system and the PL/I language include features that facilitate the formatting of printed output.
The operating system allows you to use the first byte of each record for a print control character. The control characters, which are not printed, cause the printer to skip to a new line or page. (Tables of print control characters are given in Figure 1 and Table 1.)
In a PL/I program, the use of a PRINT file provides a convenient means of controlling the layout of printed output from stream-oriented data transmission. The compiler automatically inserts print control characters in response to the PAGE, SKIP, and LINE options and format items.
You can apply the PRINT attribute to any STREAM OUTPUT file, even if you do not intend to print the associated data set directly. When a PRINT file is associated with a direct access data set, the print control characters have no effect on the layout of the data set, but appear as part of the data in the records.
PRINT files opened with FB or VB will cause the UNDEFINEDFILE condition to be raised. PRINT files should be opened with the "A" option, that is, FBA or VBA.
The compiler reserves the first byte of each record transmitted by a PRINT file for an American National Standard print control character, and inserts the appropriate characters automatically.
- Character
- Action
- Space 1 line before printing (blank character)
- 0
- Space 2 lines before printing
- -
- Space 3 lines before printing
- +
- No space before printing
- 1
- Start new page
The compiler handles the PAGE, SKIP, and LINE options or format items by padding the remainder of the current record with blanks and inserting the appropriate control character in the next record. If SKIP or LINE specifies more than a 3-line space, the compiler inserts sufficient blank records with appropriate control characters to accomplish the required spacing. In the absence of a print control option or format item, when a record is full, the compiler inserts a blank character (single line space) in the first byte of the next record.
If a PRINT file is being transmitted to a terminal, the PAGE, SKIP, and LINE options will never cause more than 3 lines to be skipped, unless formatted output is specified.