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_fdopen
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─────Run-Time Library───────────────────────────────────────────────────────
The _fdopen function associates an input/output stream with the
file identified by <handle>, thus allowing a file opened for
low-level I/O to be buffered and formatted.
Once you use _fdopen to assign a buffer to an open handle, the
file is equivalent to a stream opened with fopen. Use the new
stream, not the handle, for all subsequent I/O operations. Close
the stream with fclose, not _close. This flushes the buffer and
closes both the stream and the handle.
The <mode> character string specifies the type of access requested
for the file. Because _fdopen assumes that the <mode> argument is
a string literal, you must use quotation marks. For example:
_fdopen( handle, "rbc" );
The list below gives the <mode> string used in the fopen and
_fdopen functions. The list also shows the corresponding <oflag>
arguments used in the _open and _sopen functions. A complete
description of the <mode> string argument is given in the
description of the fopen function.
Type String _open/_sopen Equivalent Value
"r" _O_RDONLY
"w" _O_WRONLY (usually _O_WRONLY | _O_CREAT | _O_TRUNC)
"a" _O_WRONLY | _O_APPEND (usually _O_WRONLY | _O_CREAT |
_O_APPEND)
"r+" _O_RDWR
"w+" _O_RDWR (usually _O_RDWR | _O_CREAT | _O_TRUNC)
"a+" _O_RDWR | _O_APPEND (usually _O_RDWR | _O_APPEND |
_O_CREAT)
In addition to the values listed above, the "t" or "b" character
can be included in the <mode> string to specify the translation
mode for new lines. These characters correspond to the constants
used in the _open and _sopen functions, as shown below:
Mode _open/_sopen Equivalent Value
"t" _O_TEXT
"b" _O_BINARY
If "t" or "b" is not given in the <mode> string, the translation
mode is defined by the default-mode variable _fmode.
In addition to the file attribute and the text or binary mode
listed above, the <mode> string will accept either "c" or "n" to
specify commit to disk, or no commit to disk, respectively. These
characters have no correspondence to constants used in the _open
and _sopen functions.
Mode _open/_sopen Equivalent Value
"c" Commit to disk. No _open/_sopen equivalent value.
"n" Do not commit to disk. No _open/_sopen equivalent
value. Default.
If "c" or "n" is not given in the <mode> string, the default mode
is "n".
The "t", "c", and "n" options are not part of the ANSI standard,
but are instead Microsoft extensions and should not be used where
ANSI portability is desired.
Return Value
The _fdopen function returns a pointer to the open stream. A null
pointer value indicates an error.
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