Guardian Native C Library Calls Reference Manual (G06.28+, H06.04+)

freopen_guardian(3) Guardian Native C Library Calls Reference Manual
r+ Opens a text file for update (reading and writing).
w+ Truncates or creates a text file for update.
a+ Appends (opens a text file for update, writing at the end of the file, or creates a
text file for writing).
rb Opens a C binary file for reading.
wb Creates a new C binary file for writing, or opens and truncates a C binary file to
zero length.
ab Appends (opens a C binary file for writing at the end of the file, or creates a C
binary file for writing).
rb+ Opens a C binary file for update (reading and writing).
wb+ Truncates or creates a C binary file for update.
ab+ Appends (opens a C binary file for update, writing at the end of the file, or
creates a C binary file for writing).
When you open a file for update, you can perform both input and output operations on the result-
ing stream. However, an output operation cannot be directly followed by an input operation
without an intervening fflush() function call or a file positioning operation (fseek(), fsetpos(),or
rewind() function). Also, an input operation cannot be directly followed by an output operation
without an intervening flush or file positioning operation, unless the input operation encounters
the end of the file.
When you open a file for append (that is, when the mode parameter is a, ab, a+,orab+), it is
impossible to overwrite information already in the file. You can use the fseek() function to repo-
sition the file pointer to any position in the file, but when output is written to the file, the current
file pointer is ignored. All output is written at the end of the file and the file pointer is reposi-
tioned to the end of the output.
If two separate processes open the same file for append, each process can write freely to the file
without destroying the output being written by the other. The output from the two processes is
intermixed in the order in which it is written to the file. Note that if the data is buffered, it is not
actually written until it is flushed.
When opened, a stream is fully buffered if and only if it can be determined that it does not refer
to an interactive device. The error and End-of-File indicators for the stream are cleared.
The ANSISTREAMS pragma determines whether a text file is type 180 (C binary file) or type 101
(edit file). The Guardian version of freopen() distinguishes between text and binary files. If the
mode parameter does not contain a b, the file is created or opened as a text file. The OSS version
of freopen( ) does not distinguish between text and binary files. Text and binary files in the OSS
environment are type 180. Refer to the C/C++ Programmer’s Guide for information on the
ANSISTREAMS pragma.
Interoperability Variants
The C run-time library supports two variants of the freopen() function: freopen_oss() and
freopen_guardian(). The variants support the unique file naming conventions and structures of
the OSS and Guardian file systems, respectively.
The header file maps calls to freopen( ) to the variant that matches the target compilation
environment. The target environment is set with the systype pragma.
Explicit calls to the freopen_oss() and freopen_guardian() variants in source code are only
made when the behavior of one environment is desired from the other environment.
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