NAME

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 buffering scheme.  The in-line macros getc and putc(3S) handle characters quickly.  The higher level routines gets, 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(3S) 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 standard open files:

stdin standard input file

stdout standard output file

stderr standard error file

A constant ‘pointer’ NULL (0) designates no stream at all. 

An integer constant EOF (−1) 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 <stdio.h> of pertinent macro definitions. The functions and constants mentioned in sections labeled 3S are declared in the include 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.

SEE ALSO

open(2), close(2), read(2), write(2), fread(3S), fseek(3S), gets(3S), fgets(3S), scanf(3S), fscanf(3S), fread(3S), puts(3S), fputs(3S), printf(3S), fprintf(3S), fwrite(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(2) 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(2) 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(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 and abort.  Also be careful of using these functions with fork and execve. 

Sun System Release 0.3  —  1 April 1983