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 "Subscript Out of Range" for Array > 128K; Gaps in Far Heap - Q26494
 
 The program listed below when compiled with the /ah option (in
 VBDOS.EXE or BC.EXE) to support a huge (larger than 64K) array,
 produces a "Subscript out of range" error message for an array larger
 than 128K, even though the FRE(-1) function indicates that there
 should be enough available memory.
 
 To make an array larger than 128K and avoid the "Subscript out of
 range" error message, the number of bytes in each element of the huge
 array must be a power of 2 (that is, evenly divisible into 64K), as
 explained below.
 
 More Information:
 
 Space is allocated for a huge array contiguously in far heap, with the
 restriction that no single array element (or record) is allowed to be
 split across a 64K boundary. If a record size is not a power of 2,
 then BASIC allocates the first array element at an offset high enough,
 relative to the array's base segment address (returned by the VARSEG
 function), such that no array element is split across the boundary at
 exactly 64K above the base segment. (This creates a gap in the far
 heap.) The value returned by the VARPTR function for the first element
 of the array then indicates both the offset of the array, and also
 the size of a gap created in the far heap. The size of the gap is also
 equal to (65,536) MOD (array record size). This gap fragments far heap,
 and is wasted, unused memory. In the worst case, the gap can be up to
 (array record size) minus 1 in size.
 
 A "Subscript out of range" error occurs when allocating a huge array
 larger than 128K if the array elements have a size that is not an even
 power of 2. Arrays larger than 128K must have an element (or record)
 size that is a power of 2 (2, 4, 8, 16, 32, 64, etc.), since arrays
 must be stored contiguously and no single array element is allowed to
 span across a 64K boundary.
 
 You can compensate for this limitation by padding each array element
 to a size that can be evenly divided into 64K (that is, a power of 2,
 such as 4, 8, 16, 32, 64, 128, or 512 bytes), as shown in the example
 below.
 
 A huge array must be DIMensioned as a dynamic array, either with a
 variable in the array subscript or with the preceding metacommand REM
 $DYNAMIC. The /AH option allows dynamic arrays of user-defined types,
 fixed-length strings, and numeric data to occupy all of available
 memory.
 
 The following example shows how to work around the:
     ◄"Subscript out of range"► error message.
 
 The following code example demonstrates the:
     ◄"Subscript out of range"► error message.