intro.3s

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)intro.3s	8.1	9/11/90
.TH intro 3s
.SH Name
stdio \- standard buffered input/output package
.SH Syntax
.B #include <stdio.h>
.PP
.SM
.B FILE
.B *stdin;
.br
.SM
.B FILE
.B *stdout;
.br
.SM
.B FILE
.B *stderr;
.SH Description
.NXR "stdio macro package"
.NXS "standard buffered input/output package" "stdio macro package"
The functions described in section 3s constitute a user-level buffering
scheme.  The in-line macros
.PN getc
and
.MS putc 3s
handle characters quickly.  The higher level routines
.PN gets ,
.PN fgets ,
.PN scanf ,
.PN fscanf ,
.PN fread ,
.PN puts ,
.PN fputs ,
.PN printf ,
.PN fprintf ,
.PN fwrite
all use
.PN getc
and
.PN putc;
they can be freely intermixed.
.PP
A file with associated buffering is called a
.IR stream ,
and is declared to be a pointer to a defined type
.SM FILE.
.NXR "stream" "defined"
The 
.MS fopen 3s
subroutine
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:
.TP 10n
.B stdin
standard input file
.br
.ns
.TP
.B stdout
standard output file
.br
.ns
.TP
.B stderr
standard error file
.PP
A constant `pointer' NULL (0) designates no stream at all.
.PP
An integer constant EOF
(\-1) is returned upon end of file or error by integer functions that
deal with streams.
.PP
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:
.PN getc ,
.PN getchar ,
.PN putc ,
.PN putchar ,
.PN feof ,
.PN ferror ,
.PN fileno .
.NT "VAX Only"
On VAX machines, the GFLOAT version of
.IR libc
is used when you use the 
.MS cc 1
command with the 
.B \-Mg
option, or you use the 
.MS ld 1
command with the 
.B \-lcg
option.
The GFLOAT version of
.IR libc
must be used with modules 
compiled with 
.MS cc 1 
using the
.B \-Mg
option. 
.sp
Also note that neither the compiler nor the linker 
.MS ld 1
can detect when mixed double floating point types
are used, and the program may produce erroneous
results if this occurs on VAX machines.
.NE
.SH System V Compatibility
This library contains System V compatibility features that
are available to general ULTRIX programs.  For a discussion of how
these features are documented, and how to specify that the
System V environment is to be used in compiling and linking
your programs, see 
.MS intro 3 .
.SH Diagnostics
.NXR "stdio macro package" "diagnostics"
The value EOF
is returned uniformly to indicate that a FILE
pointer has not been initialized with
.PN fopen ,
input (output) has been attempted on an output (input) stream, or a
FILE pointer designates corrupt or otherwise unintelligible
FILE data.
.PP
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 
.MS 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 
.MS read 2
themselves to read from the standard input.
.PP
In cases where a large amount of computation is done after printing
part of a line on an output terminal, it is necessary to 
.MS fflush 3s
the standard output before going off and computing so that the output
will appear.
.SH Files
.nf
/lib/libc.a
/usr/lib/libcg.a   (VAX only)
.fi
.SH See Also
open(2), close(2), read(2), write(2), fread(3s), fseek(3s), ferror(3s),
fclose(3s), fopen(3s)