1.7 I/O Status Block

Figure 1-8 shows the I/O status block (IOSB) for ACP--QIO functions. Appendix A lists the status returns for these functions. (The OpenVMS system messages documentation provides explanations and suggested user actions for these returns.)

The file ACP returns a completion status in the first longword of the IOSB. In an extend operation, the second longword is used to return the number of blocks allocated to the file. If a contiguous extend operation (FIB$V_ALCON) fails, the second longword is used to return the size of the file after truncation.

Values returned in the IOSB are most useful during operations in compatibility mode. When executing programs in the native mode, use the values returned in FIB locations.

Figure 1-8 IOSB Contents — ACP-QIO Functions

If an extend operation (including CREATE) was performed, IOSB+4 contains the number of blocks allocated, or the largest available contiguous space if a contiguous extend operation failed. If a truncate operation was performed, IOSB+4 contains the number of blocks added to the file size to reach the next cluster boundary.