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stdio

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)