STDIO(3)

NAME
stdio - standard input/output library functions

SYNOPSIS
#include <stdio.h>

FILE *stdin;
FILE *stdout;
FILE *stderr;

DESCRIPTION
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) function; all output takes place as if all characters were written by successive calls to the fputc(3) 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) 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) 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 input), 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 to 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) 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 the compilers cc(1) and pc(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 re-used 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, SEE_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
    check and reset stream status

fclose
    close a stream

fdopen
    stream open functions

feof
    check and reset stream status

ferror
    check and reset stream status

fflush
    flush a stream

fgetc
    get next character or word from input stream

fgetpos
    reposition a stream

fgets
    get a line from a stream

fileno
    return the integer descriptor of the argument stream

fopen
    stream open functions

fprintf
    formatted output conversion

fpurge
    flush a stream

fputc
    output a character or word to a stream

fputs
    output a line to a stream

fread
    binary stream input/output

freopen
    stream open functions

fscanf
    input format conversion

fseek
    reposition a stream

fsetpos
    reposition a stream

ftell
    reposition a stream

fwrite
    binary stream input/output

getc
    get next character or word from input stream

getchar
    get next character or word from input stream

gets
    get a line from a stream

getw
    get next character or word from input stream

mktemp
    make temporary filename (unique)

perror
    system error messages

printf
    formatted output conversion

putc
    output a character or word to a stream

putchar
    output a character or word to a stream

puts
    output a line to a stream

putw
    output a character or word to a stream

remove
    remove directory entry

rewind
    reposition a stream

scanf
    input format conversion

setbuf
    stream buffering operations

setbuffer
    stream buffering operations

setlinebuf
    stream buffering operations

setvbuf
    stream buffering operations

sprintf
    formatted output conversion

sscanf
    input format conversion

strerror
    system error messages

sys_errlist
    system error messages

sys_nerr
    system error messages

tempnam
    temporary file routines

tmpfile
    temporary file routines

tmpnam
    temporary file routines

ungetc
    un-get character from input stream

vfprintf
    formatted output conversion

vfscanf
    input format conversion

vprintf
    formatted output conversion

vscanf
    input format conversion

vsprintf
    formatted output conversion

vsscanf
    input format conversion

CONFORMING TO
The stdio library conforms to C89.

SEE ALSO
close(2), open(2), read(2), write(2), stdout(3), unlocked_stdio(3)