fopen, freopen, fdopen, fileno, fclose, sopenr, sopenw, sclose, fflush, setvbuf, setbuf, fgetpos, ftell, fsetpos, fseek, rewind, feof, ferror, clearerr – standard buffered input/output package

#include <u.h>
#include <stdio.h>

FILE *fopen(char *filename, char *mode)

FILE *freopen(char *filename, char *mode, FILE *f)

FILE *fdopen(int fd, char *mode)

int    fileno(FILE *f)

FILE *sopenr(char *s)

FILE *sopenw(void)

char *sclose(FILE *f)

int    fclose(FILE *f)

int    fflush(FILE *f)

int    setvbuf(FILE *f, char *buf, int type, long size)

void setbuf(FILE *f, char *buf)

int    fgetpos(FILE *f, long *pos)

long ftell(FILE *f)

int    fsetpos(FILE *f, long *pos)

int    fseek(FILE *f, long offset, int whence)

void rewind(FILE *f)

int    feof(FILE *f)

int    ferror(FILE *f)

void clearerr(FILE *f)

The functions described in this and related pages (fgetc(2), fprintf(2), fscanf(2), and tmpfile(2)) implement the ANSI C buffered I/O package with extensions.

A file with associated buffering is called a stream and is declared to be a pointer to a defined type FILE. Fopen(2) creates certain descriptive data for a stream and returns a pointer to designate the stream in all further transactions. There are three normally open streams with constant pointers declared in the include file and associated with the standard open files:
stdin   standard input file
stdoutstandard output file
stderrstandard error file

A constant pointer NULL designates no stream at all.

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 operations, or NULL if the open fails. Mode is a character string having one of the following values:
"r"     open for reading
"w"     truncate to zero length or create for writing
"a"     append; open or create for writing at end of file
"r+"    open for update (reading and writing)
"w+"    truncate to zero length or create for update
"a+"    append; open or create for update at end of file

In addition, each of the above strings can have a b somewhere after the first character, meaning `binary file', but this implementation makes no distinction between binary and text files.

Fclose causes the stream pointed to by f to be flushed (see below) and does a close (see open(2)) on the associated file. It frees any automatically allocated buffer. Fclose is called automatically on exits(2) for all open streams.

Freopen is like open except that it reuses stream pointer f. Freopen first attempts to close any file associated with f; it ignores any errors in that close.

Fdopen associates a stream with an open Plan 9 file descriptor.

Fileno returns the number of the Plan 9 file descriptor associated with the stream.

Sopenr associates a read–only stream with a null–terminated string.

Sopenw opens a stream for writing. No file descriptor is associated with the stream; instead, all output is written to the stream buffer.

Sclose closes a stream opened with sopenr or sopenw. It returns a pointer to the 0 terminated buffer associated with the stream.

By default, output to a stream is fully buffered: it is accumulated in a buffer until the buffer is full, and then write (see read(2)) is used to write the buffer. An exception is standard error, which is line buffered: output is accumulated in a buffer until a newline is written. Input is also fully buffered by default; this means that read(2) is used to fill a buffer as much as it can, and then characters are taken from that buffer until it empties. Setvbuf changes the buffering method for file f according to type: either _IOFBF for fully buffered, _IOLBF for line buffered, or _IONBF for unbuffered (each character causes a read or write). If buf is supplied, it is used as the buffer and size should be its size; If buf is zero, a buffer of the given size is allocated (except for the unbuffered case) using malloc(2).

Setbuf is an older method for changing buffering. If buf is supplied, it changes to fully buffered with the given buffer, which should be of size BUFSIZ (defined in stdio.h). If buf is zero, the buffering method changes to unbuffered.

Fflush flushes the buffer of output stream f, delivering any unwritten buffered data to the host file.

There is a file position indicator associated with each stream. It starts out pointing at the first character (unless the file is opened with append mode, in which case the indicator is always ignored). The file position indicator is maintained by the reading and writing functions described in fgetc(2).

Fgetpos stores the current value of the file position indicator for stream f in the object pointed to by pos. It returns zero on success, nonzero otherwise. Ftell returns the current value of the file position indicator. The file position indicator is to be used only as an argument to fseek.

Fsetpos sets the file position indicator for stream f to the value of the object pointed to by pos, which shall be a value returned by an earlier call to fgetpos on the same stream. It returns zero on success, nonzero otherwise. Fseek obtains a new position, measured in characters from the beginning of the file, by adding offset to the position specified by whence: the beginning of the file if whence is SEEK_SET; the current value of the file position indicator for SEEK_CUR; and the end–of–file for SEEK_END. Rewind sets the file position indicator to the beginning of the file.

An integer constant EOF is returned upon end of file or error by integer–valued functions that deal with streams. Feof returns non–zero if and only if f is at its end of file.

Ferror returns non–zero if and only if f is in the error state. It can get into the error state if a system call failed on the associated file or a memory allocation failed. Clearerr takes a stream out of the error state.


fprintf(2), fscanf(2), fgetc(2)
open(2), read(2)

The value EOF is returned uniformly to indicate that a FILE pointer has not been initialized with fopen, input (output) has been attempted on an output (input) stream, or a FILE pointer designates corrupt or otherwise unintelligible FILE data.
Some of these functions set errstr.

Buffering of output can prevent output data from being seen until long after it is computed – perhaps never, as when an abort occurs between buffer filling and flushing.
Buffering of input can cause a process to consume more input than it actually uses. This can cause trouble across exec(2).
Buffering may delay the receipt of a write error until a subsequent stdio writing, seeking, or file–closing call.
ANSI says that a file can be fully buffered only if the file is not attached to an interactive device. In Plan 9 all are fully buffered except standard error.

Fdopen, fileno, sopenr, sopenw, and sclose are not ANSI Stdio functions.

Stdio offers no support for runes or UTF characters. Unless external compatibility is necessary, use bio(2), which supports UTF and is smaller, faster, and simpler than Stdio.

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