stdio(3) - Linux manual page (original) (raw)
stdio(3) Library Functions Manual stdio(3)
NAME top
stdio - standard input/output library functionsLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <stdio.h>**
**extern FILE ***_stdin_**;**
**extern FILE ***_stdout_**;**
**extern FILE ***_stderr_**;**DESCRIPTION top
The standard I/O library provides a simple and efficient buffered
stream I/O interface. Input and output is mapped into logical
data streams and the physical I/O characteristics are concealed.
The functions and macros are listed below; more information is
available from the individual man pages.
A stream is associated with an external file (which may be a
physical device) by _opening_ a file, which may involve creating a
new file. Creating an existing file causes its former contents to
be discarded. If a file can support positioning requests (such as
a disk file, as opposed to a terminal), then a _file position_
_indicator_ associated with the stream is positioned at the start of
the file (byte zero), unless the file is opened with append mode.
If append mode is used, it is unspecified whether the position
indicator will be placed at the start or the end of the file. The
position indicator is maintained by subsequent reads, writes, and
positioning requests. All input occurs as if the characters were
read by successive calls to the [fgetc(3)](../man3/fgetc.3.html) function; all output
takes place as if all characters were written by successive calls
to the [fputc(3)](../man3/fputc.3.html) function.
A file is disassociated from a stream by _closing_ the file. Output
streams are flushed (any unwritten buffer contents are transferred
to the host environment) before the stream is disassociated from
the file. The value of a pointer to a _FILE_ object is
indeterminate after a file is closed (garbage).
A file may be subsequently reopened, by the same or another
program execution, and its contents reclaimed or modified (if it
can be repositioned at the start). If the main function returns
to its original caller, or the [exit(3)](../man3/exit.3.html) function is called, all
open files are closed (hence all output streams are flushed)
before program termination. Other methods of program termination,
such as [abort(3)](../man3/abort.3.html) do not bother about closing files properly.
At program startup, three text streams are predefined and need not
be opened explicitly: _standard input_ (for reading conventional
input), _standard output_ (for writing conventional output), and
_standard error_ (for writing diagnostic output). These streams are
abbreviated _stdin_, _stdout_, and _stderr_. When opened, the standard
error stream is not fully buffered; the standard input and output
streams are fully buffered if and only if the streams do not refer
to an interactive device.
Output streams that refer to terminal devices are always line
buffered by default; pending output to such streams is written
automatically whenever an input stream that refers to a terminal
device is read. In cases where a large amount of computation is
done after printing part of a line on an output terminal, it is
necessary to [fflush(3)](../man3/fflush.3.html) the standard output before going off and
computing so that the output will appear.
The _stdio_ library is a part of the library **libc** and routines are
automatically loaded as needed by **cc**(1). The SYNOPSIS sections of
the following manual pages indicate which include files are to be
used, what the compiler declaration for the function looks like
and which external variables are of interest.
The following are defined as macros; these names may not be reused
without first removing their current definitions with **#undef**:
**BUFSIZ**, **EOF**, **FILENAME_MAX**, **FOPEN_MAX**, **L_cuserid**, **L_ctermid**,
**L_tmpnam**, **NULL**, **SEEK_END**, **SEEK_SET**, **SEEK_CUR**, **TMP_MAX**, **clearerr**,
**feof**, **ferror**, **fileno**, **getc**, **getchar**, **putc**, **putchar**, **stderr**, **stdin**,
**stdout**. Function versions of the macro functions **feof**, **ferror**,
**clearerr**, **fileno**, **getc**, **getchar**, **putc**, and **putchar** exist and will
be used if the macros definitions are explicitly removed.List of functions Function Description ─────────────────────────────────────────────────────────────────── clearerr(3) check and reset stream status fclose(3) close a stream fdopen(3) stream open functions feof(3) check and reset stream status ferror(3) check and reset stream status fflush(3) flush a stream fgetc(3) get next character or word from input stream fgetpos(3) reposition a stream fgets(3) get a line from a stream fileno(3) return the integer descriptor of the argument stream fmemopen(3) open memory as stream fopen(3) stream open functions fopencookie(3) open a custom stream fprintf(3) formatted output conversion fpurge(3) flush a stream fputc(3) output a character or word to a stream fputs(3) output a line to a stream fread(3) binary stream input/output freopen(3) stream open functions fscanf(3) input format conversion fseek(3) reposition a stream fsetpos(3) reposition a stream ftell(3) reposition a stream fwrite(3) binary stream input/output getc(3) get next character or word from input stream getchar(3) get next character or word from input stream gets(3) get a line from a stream getw(3) get next character or word from input stream mktemp(3) make temporary filename (unique) open_memstream(3) open a dynamic memory buffer stream open_wmemstream(3) open a dynamic memory buffer stream perror(3) system error messages printf(3) formatted output conversion putc(3) output a character or word to a stream putchar(3) output a character or word to a stream puts(3) output a line to a stream putw(3) output a character or word to a stream remove(3) remove directory entry rewind(3) reposition a stream scanf(3) input format conversion setbuf(3) stream buffering operations setbuffer(3) stream buffering operations setlinebuf(3) stream buffering operations setvbuf(3) stream buffering operations sprintf(3) formatted output conversion sscanf(3) input format conversion strerror(3) system error messages sys_errlist(3) system error messages sys_nerr(3) system error messages tempnam(3) temporary file routines tmpfile(3) temporary file routines tmpnam(3) temporary file routines ungetc(3) un-get character from input stream vfprintf(3) formatted output conversion vfscanf(3) input format conversion vprintf(3) formatted output conversion vscanf(3) input format conversion vsprintf(3) formatted output conversion vsscanf(3) input format conversion
STANDARDS top
C11, POSIX.1-2008.HISTORY top
C89, POSIX.1-2001.SEE ALSO top
[close(2)](../man2/close.2.html), [open(2)](../man2/open.2.html), [read(2)](../man2/read.2.html), [write(2)](../man2/write.2.html), [stdout(3)](../man3/stdout.3.html), [unlocked_stdio(3)](../man3/unlocked%5Fstdio.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-12-24 stdio(3)
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