freebsd-skq/lib/libc/stdio/stdio.3

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.\" @(#)stdio.3 8.7 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd January 10, 2003
.Dt STDIO 3
.Os
.Sh NAME
.Nm stdio
.Nd standard input/output library functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Vt FILE *stdin ;
.Vt FILE *stdout ;
.Vt FILE *stderr ;
.Sh DESCRIPTION
The standard
.Tn I/O
library provides a simple and efficient buffered stream
.Tn I/O
interface.
Input and output is mapped into logical data streams
and the physical
.Tn I/O
characteristics are concealed.
The functions and macros are listed
below; more information is available from the individual man pages.
.Pp
A stream is associated with an external file (which may be a physical
device) by
.Em 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
.Em 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, the position indicator will be placed at the end-of-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
.Xr fgetc 3
function; all output takes place as if all characters were
written by successive calls to the
.Xr fputc 3
function.
.Pp
A file is disassociated from a stream by
.Em 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
.Dv FILE
object is indeterminate (garbage) after a file is closed.
.Pp
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
.Xr exit 3
function is called, all open files are closed (hence all output
streams are flushed) before program termination. Other methods
of program termination may not close files properly and hence
buffered output may be lost. In particular,
.Xr _exit 2
does not flush stdio files. Neither does an exit due to a signal.
Buffers are flushed by
.Xr abort 3
as required by POSIX, although previous implementations did not.
.Pp
This implementation makes no distinction between
.Dq text
and
.Dq binary
streams.
In effect, all streams are binary.
No translation is performed and no extra padding appears on any stream.
.Pp
At program startup, three streams are predefined and need not be
opened explicitly:
.Bl -bullet -compact -offset indent
.It
.Em standard input
(for reading conventional input),
.It
.Em standard output
(for writing conventional output), and
.It
.Em standard error
(for writing diagnostic output).
.El
These streams are abbreviated
.Dv stdin , stdout
and
.Dv stderr .
Initially, the standard error stream
is unbuffered; the standard input and output streams are
fully buffered if and only if the streams do not refer to
an interactive or
.Dq terminal
device, as determined by the
.Xr isatty 3
function.
In fact,
.Em all
freshly-opened streams that refer to terminal devices
default to line buffering, and
pending output to such streams is written automatically
whenever such an input stream is read.
Note that this applies only to
.Dq "true reads" ;
if the read request can be satisfied by existing buffered data,
no automatic flush will occur.
In these cases,
or when a large amount of computation is done after printing
part of a line on an output terminal, it is necessary to
.Xr fflush 3
the standard output before going off and computing so that the output
will appear.
Alternatively, these defaults may be modified via the
.Xr setvbuf 3
function.
.Pp
The
.Nm
library is a part of the library
.Nm libc
and routines are automatically loaded as needed by the C compiler.
The
.Tn 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.
.Pp
The following are defined as macros;
these names may not be re-used
without first removing their current definitions with
.Ic #undef :
.Dv BUFSIZ ,
.Dv EOF ,
.Dv FILENAME_MAX ,
.Dv FOPEN_MAX ,
.Dv L_ctermid ,
.Dv L_cuserid ,
.Dv L_tmpnam ,
.Dv NULL ,
.Dv P_tmpdir ,
.Dv SEEK_CUR ,
.Dv SEEK_END ,
.Dv SEEK_SET ,
.Dv TMP_MAX ,
.Dv clearerr ,
.Dv clearerr_unlocked ,
.Dv feof ,
.Dv feof_unlocked ,
.Dv ferror ,
.Dv ferror_unlocked ,
.Dv fileno ,
.Dv fileno_unlocked ,
.Dv fropen ,
.Dv fwopen ,
.Dv getc ,
.Dv getc_unlocked ,
.Dv getchar ,
.Dv getchar_unlocked ,
.Dv putc ,
.Dv putc_unlocked ,
.Dv putchar ,
.Dv putchar_unlocked ,
.Dv stderr ,
.Dv stdin
and
.Dv stdout .
Function versions of the macro functions
.Dv clearerr ,
.Dv clearerr_unlocked ,
.Dv feof ,
.Dv feof_unlocked ,
.Dv ferror ,
.Dv ferror_unlocked ,
.Dv fileno ,
.Dv fileno_unlocked ,
.Dv getc ,
.Dv getc_unlocked ,
.Dv getchar ,
.Dv getchar_unlocked ,
.Dv putc ,
.Dv putc_unlocked ,
.Dv putchar ,
and
.Dv putchar_unlocked
exist and will be used if the macro
definitions are explicitly removed.
.Sh SEE ALSO
.Xr close 2 ,
.Xr open 2 ,
.Xr read 2 ,
.Xr write 2
.Sh BUGS
The standard buffered functions do not interact well with certain other
library and system functions, especially
.Xr vfork 2 .
.Sh STANDARDS
The
.Nm
library conforms to
.St -isoC-99 .
.Sh LIST OF FUNCTIONS
.Bl -column "Description"
.It Sy "Function Description"
.It "asprintf formatted output conversion"
.It "clearerr check and reset stream status"
.It "fclose close a stream"
.It "fdopen stream open functions"
.It "feof check and reset stream status"
.It "ferror check and reset stream status"
.It "fflush flush a stream"
.It "fgetc get next character or word from input stream"
.It "fgetln get a line from a stream"
.It "fgetpos reposition a stream"
.It "fgets get a line from a stream"
.It "fgetwc get next wide character from input stream"
.It "fgetws get a line of wide characters from a stream"
.It "fileno check and reset stream status"
.It "fopen stream open functions"
.It "fprintf formatted output conversion"
.It "fpurge flush a stream"
.It "fputc output a character or word to a stream"
.It "fputs output a line to a stream"
.It "fputwc output a wide character to a stream"
.It "fputws output a line of wide characters to a stream"
.It "fread binary stream input/output"
.It "freopen stream open functions"
.It "fropen open a stream"
.It "fscanf input format conversion"
.It "fseek reposition a stream"
.It "fsetpos reposition a stream"
.It "ftell reposition a stream"
.It "funopen open a stream"
.It "fwide set/get orientation of stream"
.It "fwopen open a stream"
.It "fwprintf formatted wide character output conversion"
.It "fwrite binary stream input/output"
.It "getc get next character or word from input stream"
.It "getchar get next character or word from input stream"
.It "gets get a line from a stream"
.It "getw get next character or word from input stream"
.It "getwc get next wide character from input stream"
.It "getwchar get next wide character from input stream"
.It "mkdtemp create unique temporary directory"
.It "mkstemp create unique temporary file"
.It "mktemp create unique temporary file"
.It "perror system error messages"
.It "printf formatted output conversion"
.It "putc output a character or word to a stream"
.It "putchar output a character or word to a stream"
.It "puts output a line to a stream"
.It "putw output a character or word to a stream"
.It "putwc output a wide character to a stream"
.It "putwchar output a wide character to a stream"
.It "remove remove directory entry"
.It "rewind reposition a stream"
.It "scanf input format conversion"
.It "setbuf stream buffering operations"
.It "setbuffer stream buffering operations"
.It "setlinebuf stream buffering operations"
.It "setvbuf stream buffering operations"
.It "snprintf formatted output conversion"
.It "sprintf formatted output conversion"
.It "sscanf input format conversion"
.It "strerror system error messages"
.It "swprintf formatted wide character output conversion"
.It "sys_errlist system error messages"
.It "sys_nerr system error messages"
.It "tempnam temporary file routines"
.It "tmpfile temporary file routines"
.It "tmpnam temporary file routines"
.It "ungetc un-get character from input stream"
.It "ungetwc un-get wide character from input stream"
.It "vasprintf formatted output conversion"
.It "vfprintf formatted output conversion"
.It "vfscanf input format conversion"
.It "vfwprintf formatted wide character output conversion"
.It "vprintf formatted output conversion"
.It "vscanf input format conversion"
.It "vsnprintf formatted output conversion"
.It "vsprintf formatted output conversion"
.It "vsscanf input format conversion"
.It "vswprintf formatted wide character output conversion"
.It "vwprintf formatted wide character output conversion"
.It "wprintf formatted wide character output conversion"
.El