STDIO(3S) STDIO(3S)
NAME
stdio - standard buffered input/output package
SYNOPSIS
#include <stdio.h>
FILE *stdin;
FILE *stdout;
FILE *stderr;
DESCRIPTION
The functions described in Sections 3S constitute an effi-
cient user-level buffering scheme. The in-line macros
getc(3) and putc handle characters quickly. The higher
level routines fgets, scanf, fscanf, fread, puts, fputs,
printf, fprintf, fwrite all 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(3)
creates certain descriptive data for a stream and returns a
pointer to designate the stream in all further transactions.
There are three normally open streams with constant pointers
declared in the include file and associated with the stan-
dard open files:
stdin standard input file
stdout standard output file
stderr standard error file
A constant pointer NULL designates no stream at all.
An integer constant EOF is returned upon end of file or
error by integer functions that deal with streams.
Any routine that uses the standard input/output package must
include the header file of pertinent macro definitions. The
functions and constants mentioned in sections labeled 3S are
declared in the include file and need no further declara-
tion. The constants, and the following `functions' are
implemented as macros: getc, getchar, putc, putchar, feof,
ferror, fileno.
SEE ALSO
printf(3), scanf(3), fopen(3), getc(3), fgets(3), fread(3),
fseek(3), ungetc(3), popen(3), setbuf(3), ferror(3)
open(2), read(2), fio(3)
DIAGNOSTICS
The value EOF is returned uniformly to indicate that a FILE
STDIO(3S) STDIO(3S)
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.
BUGS
Buffering of output can prevent output data from being seen
until long after it is computed - perhaps never, as when an
abort occurs between buffer filling and flushing.
Buffering of input can cause a process to consume more input
than it actually uses. This can cause trouble across
exec(2) or system(3) calls.
BUffering may delay the receipt of a write error until a
subsequent stdio writing, seeking, or file-closing call.