INTRO(3S)

NAME
intro, stdio - standard buffered input/output package

SYNOPSIS
#include <stdio.h>

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

DESCRIPTION
The functions described in section 3S constitute a user-level I/O buffering scheme. The in-line macros getc and putc(3S) handle characters quickly. The macros getchar and putchar, and the higher level routines fgetc, getw, gets, fgets, scanf, fscanf, fread, fputc, putw, puts, fputs, printf, fprintf, fwrite all use or act as if they use getc and putc; they can be freely intermixed.

A file with associated buffering is called a stream, and is declared to be a pointer to a defined type FILE. fopen(3S) creates certain descriptive data for a stream and returns a pointer to designate the stream in all further transactions. Normally, there are three open streams with constant pointers declared in the <stdio.h> include file and associated with the standard open files:

stdin
    standard input file

stdout
    standard output file

stderr
    standard error file

A constant NULL (0) designates a nonexistent pointer.

An integer constant EOF (-1) is returned upon end-of-file or error by most integer functions that deal with streams (see the individual descriptions for details).

Any module that uses this package must include the header file of pertinent macro definitions, as follows:

    #include <stdio.h>

The functions and constants mentioned in sections labeled 3S of this manual are declared in that header file and need no further declaration. The constants and the following `functions' are implemented as macros; redeclaration of these names is perilous: getc, getchar, putc, putchar, feof, ferror, fileno, and clearerr.

SEE ALSO
open(2V), close(2), lseek(2), pipe(2), read(2V), write(2V), ctermid(3S), cuserid(3S), fclose(3S), ferror(3S), fopen(3S), fread(3S), fseek(3S), getc(3S), gets(3S), popen(3S), printf(3S), putc(3S), puts(3S), scanf(3S), setbuf(3S), system(3), tmpfile(3S), tmpnam(3S), ungetc(3S).

DIAGNOSTICS
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.

For purposes of efficiency, this implementation of the standard library has been changed to line buffer output to a terminal by default and attempts to do this transparently by flushing the output whenever a read(2V) from the standard input is necessary. This is almost always transparent, but may cause confusion or malfunctioning of programs which use standard I/O routines but use read(2V) themselves to read from the standard input.

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 (see fclose(3S)) the standard output before going off and computing so that the output will appear.

BUGS
The standard buffered functions do not interact well with certain other library and system functions, especially vfork.

LIST OF FUNCTIONS

Name	Appears on Page	Description
clearerr	ferror(3S)	stream status inquiries
ctermid	ctermid(3S)	generate filename for terminal
cuserid	cuserid(3S)	get character login name of user
fclose	fclose(3S)	close or flush a stream
fdopen	fopen(3S)	open a stream
feof	ferror(3S)	stream status inquiries
ferror	ferror(3S)	stream status inquiries
fflush	fclose(3S)	close or flush a stream
fgetc	getc(3S)	get character or integer from stream
fgets	gets(3S)	get a string from a stream
fileno	ferror(3S)	stream status inquiries
fopen	fopen(3S)	open a stream
fprintf	printf(3S)	formatted output conversion
fputc	putc(3S)	put character or word on a stream
fputs	puts(3S)	put a string on a stream
fread	fread(3S)	buffered binary input/output
freopen	fopen(3S)	open a stream
fscanf	scanf(3S)	formatted input conversion
fseek	fseek(3S)	reposition a stream
ftell	fseek(3S)	reposition a stream
fwrite	fread(3S)	buffered binary input/output
getc	getc(3S)	get character or integer from stream
getchar	getc(3S)	get character or integer from stream
gets	gets(3S)	get a string from a stream
getw	getc(3S)	get character or integer from stream
pclose	popen(3S)	initiate I/O to/from a process
popen	popen(3S)	initiate I/O to/from a process
printf	printf(3S)	formatted output conversion
putc	putc(3S)	put character or word on a stream
putchar	putc(3S)	put character or word on a stream
puts	puts(3S)	put a string on a stream
putw	putc(3S)	put character or word on a stream
rewind	fseek(3S)	reposition a stream
scanf	scanf(3S)	formatted input conversion
setbuf	setbuf(3S)	assign buffering to a stream
setbuffer	setbuf(3S)	assign buffering to a stream
setlinebuf	setbuf(3S)	assign buffering to a stream
sprintf	printf(3S)	formatted output conversion
sscanf	scanf(3S)	formatted input conversion
ungetc	ungetc(3S)	push character back into input stream
vfprintf	vprintf(3S)	print formatted varargs output
vprintf	vprintf(3S)	print formatted varargs output
vsprintf	vprintf(3S)	print formatted varargs output