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Error -28801 or -28706 from FDget (5/13/96)

Q: Why does the FDget function return error -28801 (Out of heap memory) or -28706 (Invalid parameter)? I don't think I'm out of memory, and I don't always get this error code so my parameters must be right. What is wrong?

A: Sometimes these error codes are accurate and indicate that not enough memory could be allocated or that a parameter was invalid. Sometimes they are the result of a bug caused by having multiple copies of a rectangle slot inside a frame.

The protocol which is used to send frames can perform an optimization for certain rectangle frames, which transmits them in a compact form (5 bytes instead of up to 60). However, if a given frame holds the exact same rectangle frame in more than one slot, the data will not be handled correctly and will either result in one of these error codes, or alternatively it might substitute some other object in place of the frame, or might possibly crash.

This is a relatively uncommon problem, since all of the values in the frame must be between 0 and 255, and the frame must have the same rectangle in it twice - two frames with equivalent data would not trigger the problem. For example, frame "A" would cause the problem, but frames "B", "C" and "D" would not.

A:={first: {left:3, right: 30, top:10, bottom:90}};
A.second := A.first;           // triggers the problem

B:={first: {left:3, right: 30, top:10, bottom:90}};
B.second := clone(B.first);    // cloning avoids the problem

C:={first: {left:3, right: 30, top:10, bottom:90, foo: nil}};
C.second := C.first;           // no problem since C.foo exists

D:={first: {left:3, right: 30, top:10, bottom:1000}};
D.second := D.first;       // no problem since D.bottom is >255

To work around this problem, you can clone the frame (as in frame "B") or add another slot to the frame (as in frame "C") or ensure that the values are not between 0 and 255 (frame "D").

Note: this has been fixed in the 1.0.2 Windows DILs.