fopen, freopen, fdopen - open a stream
FILE *fopen(const char *filename, const char *type)
FILE *freopen(const char *filename, const char *type, FILE *stream)
FILE *fdopen(int fildes, const char *type)
Fopen opens the file named by filename and associates a stream with it.
Fopen returns a pointer to be used to identify the stream in subsequent
Type is a character string having one of the following values:
"r" open for reading
"w" create for writing
"a" append: open for writing at end of file, or create for writing
In addition, each type may be followed by a "+" to have the file opened
for reading and writing. "r+" positions the stream at the beginning of
the file, "w+" creates or truncates it, and "a+" positions it at the end.
Both reads and writes may be used on read/write streams, with the
limitation that an fseek, rewind, or reading an end-of-file must be used
between a read and a write or vice-versa.
Freopen substitutes the named file in place of the open stream. It
returns the original value of stream. The original stream is closed.
Freopen is typically used to attach the preopened constant names, stdin,
stdout, stderr, to specified files.
Fdopen associates a stream with a file descriptor obtained from open,
dup, creat, or pipe(2). The type of the stream must agree with the mode
of the open file.
Fopen and freopen return the pointer NULL if filename cannot be accessed,
if too many files are already open, or if other resources needed cannot
Fdopen is not portable to systems other than UNIX.
The read/write types do not exist on all systems. Those systems without
read/write modes will probably treat the type as if the "+" was not
present. These are unreliable in any event.