The $CHAIN statement allows source code to be read in from an external file item.
Format
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$CHAIN[filename] item-ID |
Parameter(s)
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filename |
Name of the file containing the item. If filename is omitted, the current file is assumed. |
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item-ID |
item-ID of the item containing the source code |
Description
The $CHAIN statement directs the compiler to read source code from the specified file item and compile it as if it were written directly in the current program. The $CHAIN statement differs from the $INCLUDE and $INSERT statements in that the compiler does not return to the main program after compiling the source code in the specified file item; any statements appearing after the $CHAIN statement are ignored.
PC/OS versions prior to Mentor PRO 4.0 limited the size of items to 32K. Therefore, the $CHAIN statement was designed for programs with source code larger than 32K. By using $CHAIN statements, very long source code may be broken up into several file items and $CHAINed together, as long as the object code does not exceed 248K.
Example
To transfer compilation to source code in item PROG2 in file BP, the code might read:
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$CHAIN BP PROG2 |
In the next example, a very long program is broken up into 3 different source file items, each one but the last ending with a $CHAIN statement that calls the next.
The source file item CUST.ENTRY:
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EQUATE TRUE TO 1, FALSE TO 0, AM TO CHAR (254), VM TO CHAR (253), . . . PRINT "PRINT REPORTS?" $CHAIN CUST.ENTRY2 At the end of CUST.ENTRY, source file item CUST.ENTRY2 is called with a $CHAIN statement. CUST.ENTRY2 contains: INPUT ANSWER . . . FOUND = FALSE FOR I = 1 TO NO.OF.ELTS UNTIL FOUND IF CUST.ARRAY (I) < 1, 3 > = NAME THEN $CHAIN CUST.ENTRY3 CUST.ENTRY2, in turn, calls CUST.ENTRY3, which reads: FOUND = TRUE END NEXT I . . . |
Note in the example that a FOR loop and an IF construct are broken over two file items.
See Also