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fopen() opens the file named by file and associates a stream with it. If the open succeeds, fopen() returns a pointer to be used to identify
the stream in subsequent operations.
file points to a character string that contains the name of the file to be opened.
mode is a character string having one of the following values:
-
r
- open for reading
-
w
- truncate or create for writing
-
a
- append: open for writing at end of file, or create for writing
-
r+
- open for update (reading and writing)
-
w+
- truncate or create for update
-
a+
- append; open or create for update at EOF
freopen() opens the file named by file and associates the stream pointed to by iop with it. The mode argument
is used just as in fopen(). The original stream is closed, regardless of whether the open ultimately succeeds. If the open succeeds, freopen() returns the original
value of iop.
freopen() is typically used to attach the preopened streams associated with stdin, stdout, and stderr to other files.
When a file is opened for update, both input and output may be done on the resulting stream. However, output may not be directly followed by input without an intervening fseek(3C) or rewind(3C), and input may not be directly followed by output without an intervening fseek(3C) or rewind(3C). An input operation which encounters EOF will fail.
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