Writing to and updating text and binary I/O files

KSDS, KSDS AIX, and ESDS AIX
z/OS® XL C/C++ VSAM support for streams does not provide for writing and updating these types of data sets opened for text or binary stream I/O.
ESDS
Writes are supported for ESDSs opened as binary or text streams. Updating data in an ESDS stream cannot change the length of the record in the external file. Therefore, in a binary stream:
- updates for less than the existing record length leave existing data beyond the updated length unchanged;
- updates for longer than the existing record length flow over the record boundary and update the start of the next record.
In text streams:
- updates that specify records shorter than the original record pad the updated record to the existing record length with blanks;
- updates for longer than the existing record length result in truncation, unless the original record contained only a new-line character, in which case it may be updated to contain one byte of data plus a new-line character.
RRDS
fwrite() is called with a character buffer instead of an RRDS record structure.

Records are treated as contiguous. Once the current record is filled, the next record in the file is written to. For example, if the file consisted of only record 1, record 5, and record 28, a write would complete record 1 and then go directly to record 5.

Writing past the last record in the file is allowed, up to the maximum size of the RRDS data set. For example, if the last record in the file is record 28, the next record to be written is record 29.

Insertion of records is not supported. For example, in a file of records 1, 5, and 28, you cannot insert record 3 into the file.