Controlling Page Breaks

Learning Objective

By the end of this lesson, you will be able to explain the difference between automatic page overflow and a deliberate page break triggered by a change in the underlying data, and write a simple example of the latter.

Simple Explanation

The Page Overflow Basics lesson covered overflow that IBM i triggers automatically once a page fills up. Sometimes a report needs a new page to start deliberately, based on the data itself, rather than waiting for the page to physically fill. A common example is starting a new page every time the data moves to a new group, such as a new customer's orders.

dcl-f CUSTRPTP printer;
dcl-f ORDHIST disk keyed;

dcl-s prevCustNbr packed(6:0) inz(0);

write HDGFMT;

read ORDHIST;
dow not %eof(ORDHIST);
  if CUSTNBR <> prevCustNbr and prevCustNbr <> 0;
    write HDGFMT;
  endif;

  write DTLFMT;
  prevCustNbr = CUSTNBR;

  read ORDHIST;
enddo;

Here, prevCustNbr remembers the customer number from the previous record. Each pass compares the current record's CUSTNBR against it: if they differ, and this is not simply the very first record, write HDGFMT; forces a new page before printing that customer's first order, regardless of whether the current page happens to be physically full. This is a deliberate, data-driven page break, distinct from the automatic overflow indicator check covered in the Page Overflow Basics lesson.

Why It Matters

Automatic overflow alone cannot express "start a new page whenever the customer changes"; it only knows when a page is physically full. Recognizing that a report can also force a new page based on a change in the data itself, commonly called a control break, is essential for producing reports organized by group, such as one page per customer or one section per region.

Practical Example

Imagine a report listing every order in ORDHIST, organized so that each customer's orders start on a fresh page, making it easy for someone to pull out just one customer's section. As the program reads through ORDHIST in customer order, it compares each order's customer number against the previous one; the moment the customer number changes, it forces a new page before printing that customer's next order, exactly as shown above.

This is a simplified, illustrative example rather than a specific real report, but it reflects a genuinely common report requirement: organizing printed output by group rather than leaving page breaks purely to chance.

Common Confusions

"Is a control break the same thing as page overflow?" No. Page overflow, covered in the Page Overflow Basics lesson, is automatic and based purely on how much of the current page is already used. A control break is deliberate and based on the data itself, such as a key field changing from one record to the next, regardless of how full the page is.

"Why does the example check prevCustNbr <> 0 as well as CUSTNBR <> prevCustNbr?" Without that extra check, the very first record would also be treated as a customer change, since prevCustNbr starts at zero and no real customer number equals zero. The extra check specifically avoids forcing an unnecessary page break before the very first order has even printed.

"Can a report use both automatic overflow and a deliberate control break together?" Yes. A single report can check both conditions, forcing a new page either when the page overflows automatically or when a control break in the data occurs, whichever happens first; this lesson focuses on the control break specifically, building on the overflow check already covered.

Quick Recap

• Automatic page overflow, covered in the Page Overflow Basics lesson, is based purely on how full the current page is.
• A control break forces a deliberate new page based on a change in the underlying data, such as a customer number changing from one record to the next.
• Remembering the previous record's key value, and comparing it to the current record's, is the basic mechanism behind detecting a control break.
• A report can combine both automatic overflow and a deliberate control break in the same program.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "How would this pattern change if the report needed to break on a region field instead of a customer number?"
• "Could a control break also be used to print a subtotal for each customer, rather than just forcing a new page?"