Guardian Native C Library Calls Reference Manual (G06.29+, H06.08+, J06.03+)

fopen(3) Guardian Native C Library Calls Reference Manual
NAME
fopen - Opens a file stream
LIBRARY
G-series native Guardian processes: $SYSTEM.SYSnn.ZCRTLSRL
G-series native OSS processes: /G/system/sysnn/zcrtlsrl
H-series and J-series native Guardian processes: $SYSTEM.ZDLLnnn.ZCRTLDLL
32-bit H-series and J-series OSS processes: /G/system/zdllnnn/zcrtldll
64-bit H-series and J-series OSS processes: /G/system/zdllnnn/ycrtldll
DESCRIPTION
The C run-time library supports two variants of the fopen( ) function: fopen_oss() and
fopen_guardian(). These variants support the unique file-naming conventions and structures of
the OSS and Guardian file systems, respectively. These variants support OSS files that have a file
offset maximum smaller than 2 gigabytes and Guardian files that have a file offset maximum
smaller than 4 gigabytes (Guardian Format 1 files).
For the TNS C runtime library only, the header file maps calls to fopen( ) to the variant that
matches the target compilation environment. The target environment is set with the systype
pragma.
Explicit calls to the fopen_oss() and fopen_guardian() variants in source code are only made
when the behavior of one environment is desired from the other environment.
For a description of the fopen( ) OSS function and the fopen_oss( ) function, refer to the
fopen_oss(3) reference page. For a description of the fopen() Guardian function and the
fopen_guardian() function, see the fopen_guardian(3) reference page.
For a description of equivalent functions that support OSS files that have a file offset maximum
larger than 2 gigabytes and Guardian files that have a file offset maximum larger than 4 gigabytes
(Guardian Format 2 files), see the fopen64(3) reference page.
NOTES
The file offset maximum for an OSS file is established when the file is opened:
• When you use fopen64_oss(), or a function that calls this function, to open an OSS file
that has a file offset maximum of 2 gigabytes, the file is automatically converted to a file
that can grow to larger than 2 gigabytes.
• When you use fopen_oss() (and the call is not mapped to fopen64_oss()) to open a file
that is larger than 2 gigabytes, the file is treated like a small file. Subsequent operations,
such as read, write, and positioning operations, are subject to the same limits as when
accessing a file that has an offset maximum of 2 gigabytes.
The file offset maximum for an Guardian file is established when the file is opened. When you
use fopen_guardian() (and the call is not mapped to fopen64_guardian()) to open a Guardian
Format 2 file that has less than 4 gigabytes of data, the file is treated like a Guardian Format 1
file. Subsequent operations, such as read, write, and positioning operations, are subject to the
same limits as when accessing a Guardian Format 1 file (that has an offset maximum of 4 giga-
bytes). For a few functions, the OSS limit for small files of 2 gigabytes applies instead of the
Guardian limit for small files of 4 gigabytes, because file positions beyond 2 gigabytes cannot be
represented in the functions’s data structures.
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