Accessing Files Programmer's Guide (32650-90885)

Chapter 2 61
Creating A File
Specifying Record Size
Specifying Record Size
You can specify the size of the records in your file by using the BUILD (for disk files) or FILE
commands, or the HPFOPEN/FOPEN intrinsic; however, the interpretation of the requested
record size can be affected by the record structure and data format chosen as well as the
device for the file.
NOTE Within MPE/iX and in various subsystems, the record size for an ASCII file is
usually identified in terms of bytes (8 bits) and the record size for a binary file
is identified in terms of half-words (16 bits). This convention is a matter of
convenience only, since most users think of ASCII files as being character
oriented.
When you specify the record size for a fixed-length ASCII file, the record size determined
for the file is the same as that which you specified for it. The maximum record size allowed
for fixed-length ASCII files is 32767 bytes.
To maintain compatibility with pre-900 Series HP 3000 computer systems, the following
file types always begin records on half-word boundaries:
• ASCII files with variable-length or undefined-length record format
• binary files with fixed-length, variable-length, or undefined-length record format
For these file types, when you specify an odd-byte record size, the file system rounds up the
value to an even number to reflect the fact that these records always begin on half-word
boundaries. The maximum record size you can specify for these file types is 32766 bytes.
When the file is a binary file or a variable-length ASCII file, the extra byte is available to
be used for data. Figure 2-5. illustrates the placement of odd-bytes records and the
disposition of the added byte.