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.sp 100
.TL
.ft R
Appendix \(em The Standard I/O Library
.AU
D. M. Ritchie
.AI
AT&T Bell Laboratories
Murray Hill, NJ 07974
.PP
The standard I/O library
was designed with the following goals in mind.
.IP 1.
It must be as efficient as possible, both in time and in space,
so that there will be no hesitation in using it
no matter how critical the application.
.IP 2.
It must be simple to use, and also free of the magic
numbers and mysterious calls
whose use mars the understandability and portability
of many programs using older packages.
.IP 3.
The interface provided should be applicable on all machines,
whether or not the programs which implement it are directly portable
to other systems,
or to machines other than the PDP-11 running a version of
.UC UNIX .
.SH
1.  General Usage
.PP
Each program using the library must have the line
.P1
		#include <stdio.h>
.P2
which defines certain macros and variables.
The routines are in the normal C library,
so no special library argument is needed for loading.
All names in the include file intended only for internal use begin
with an underscore
.UL _
to reduce the possibility
of collision with a user name.
The names intended to be visible outside the package are
.IP \f3stdin\f1 10
The name of the standard input file
.IP \f3stdout\f1 10
The name of the standard output file
.IP \f3stderr\f1 10
The name of the standard error file
.IP \f3EOF\f1 10
is actually \-1, and is the value returned by
the read routines on end-of-file or error.
.IP \f3NULL\f1 10
is a notation for the null pointer, returned by
pointer-valued functions
to indicate an error
.IP \f3FILE\f1 10
expands to
.UL struct
.UL _iob
and is a useful
shorthand when declaring pointers
to streams.
.IP \f3BUFSIZ\f1 10
is a number (viz. 512)
of the size suitable for an I/O buffer supplied by the user.
See
.UL setbuf ,
below.
.IP \f3getc,\ getchar,\ putc,\ putchar,\ feof,\ ferror,\ f\&ileno\f1 10
.br
are defined as macros.
Their actions are described below;
they are mentioned here
to point out that it is not possible to
redeclare them
and that they are not actually functions;
thus, for example, they may not have breakpoints set on them.
.PP
The routines in this package
offer the convenience of automatic buffer allocation
and output flushing where appropriate.
The names
.UL stdin ,
.UL stdout ,
and
.UL stderr
are in effect constants and may not be assigned to.
.SH
2.  Calls
.nr PD .4v
.LP
.UL FILE\ *fopen(filename,\ type)\ char\ *filename,\ *type;
.nr PD 0
.IP
.br
opens the file and, if needed, allocates a buffer for it.
.UL filename
is a character string specifying the name.
.UL type
is a character string (not a single character).
It may be
.UL \&"r" ,
.UL \&"w" ,
or
.UL \&"a"
to indicate
intent to read, write, or append.
The value returned is a file pointer.
If it is
.UL  NULL
the attempt to open failed.
.ne 3
.nr PD .4v
.LP
.UL FILE\ *freopen(filename,\ type,\ ioptr)\ char\ *filename,\ *type;\ FILE\ *ioptr;
.nr PD 0
.IP
.br
The stream named by
.UL ioptr
is closed, if necessary, and then reopened
as if by
.UL fopen .
If the attempt to open fails,
.UL  NULL
is returned,
otherwise
.UL ioptr ,
which will now refer to the new file.
Often the reopened stream is
.UL stdin
or
.UL stdout .
.nr PD .4v
.LP
.UL int\ getc(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
returns the next character from the stream named by
.UL ioptr ,
which is a pointer to a file such as returned by
.UL fopen ,
or the name
.UL stdin .
The integer
.UL  EOF
is returned on end-of-file or when
an error occurs.
The null character
.UL \e0
is a legal character.
.nr PD .4v
.LP
.UL int\ fgetc(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
acts like
.UL getc
but is a genuine function,
not a macro,
so it can be pointed to, passed as an argument, etc.
.nr PD .4v
.LP
.UL putc(c,\ ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
.UL putc
writes the character
.UL c
on the output stream named by
.UL ioptr ,
which is a value returned from
.UL fopen
or perhaps
.UL stdout
or
.UL stderr .
The character is returned as value,
but
.UL  EOF
is returned on error.
.nr PD .4v
.LP
.UL fputc(c,\ ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
acts like
.UL putc
but is a genuine
function, not a macro.
.nr PD .4v
.LP
.UL fclose(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
The file corresponding to
.UL ioptr
is closed after any buffers are emptied.
A buffer allocated by the I/O system is freed.
.UL fclose
is automatic on normal termination of the program.
.nr PD .4v
.LP
.UL fflush(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
Any buffered information on the (output) stream named by
.UL ioptr
is written out.
Output files are normally buffered
if and only if they are not directed to the terminal;
however,
.UL stderr
always starts off unbuffered and remains so unless
.UL setbuf
is used, or unless it is reopened.
.nr PD .4v
.LP
.UL exit(errcode);
.nr PD 0
.IP
.br
terminates the process and returns its argument as status
to the parent.
This is a special version of the routine
which calls
.UL fflush
for each output file.
To terminate without flushing,
use
.UL _exit .
.nr PD .4v
.LP
.UL feof(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
returns non-zero when end-of-file
has occurred on the specified input stream.
.nr PD .4v
.LP
.UL ferror(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
returns non-zero when an error has occurred while reading
or writing the named stream.
The error indication lasts until the file has been closed.
.nr PD .4v
.LP
.UL getchar();
.nr PD 0
.IP
.br
is identical to
.UL getc(stdin) .
.nr PD .4v
.LP
.UL putchar(c);
.nr PD 0
.IP
.br
is identical to
.UL putc(c,\ stdout) .
.nr PD .4v
.nr PD .4v
.ne 2
.LP
.UL char\ *fgets(s,\ n,\ ioptr)\ char\ *s;\ FILE\ *ioptr;
.nr PD 0
.IP
.br
reads up to
.UL n-1
characters from the stream
.UL ioptr
into the character pointer
.UL s .
The read terminates with a newline character.
The newline character is placed in the buffer
followed by a null character.
.UL fgets
returns the first argument,
or
.UL  NULL
if error or end-of-file occurred.
.nr PD .4v
.nr PD .4v
.LP
.UL fputs(s,\ ioptr)\ char\ *s;\ FILE\ *ioptr;
.nr PD 0
.IP
.br
writes the null-terminated string (character array)
.UL s
on the stream
.UL ioptr .
No newline is appended.
No value is returned.
.nr PD .4v
.LP
.UL ungetc(c,\ ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
The argument character
.UL c
is pushed back on the input stream named by
.UL ioptr .
Only one character may be pushed back.
.ne 5
.nr PD .4v
.LP
.UL printf(format,\ a1,\ ...)\ char\ *format;
.br
.UL fprintf(ioptr,\ format,\ a1,\ ...)\ FILE\ *ioptr;\ char\ *format;
.br
.UL sprintf(s,\ format,\ a1,\ ...)char\ *s,\ *format;
.br
.nr PD 0
.IP
.UL printf
writes on the standard output.
.UL fprintf
writes on the named output stream.
.UL sprintf
puts characters in the character array (string)
named by
.UL s .
The specifications are as described in section
.UL printf (3)
of the
.ul
.UC UNIX
.ul
Programmer's Manual.
.nr PD .4v
.LP
.UL scanf(format,\ a1,\ ...)\ char\ *format;
.br
.UL fscanf(ioptr,\ format,\ a1,\ ...)\ FILE\ *ioptr;\ char\ *format;
.br
.UL sscanf(s,\ format,\ a1,\ ...)\ char\ *s,\ *format;
.nr PD 0
.IP
.br
.UL scanf
reads from the standard input.
.UL fscanf
reads from the named input stream.
.UL sscanf
reads from the character string
supplied as
.UL s .
.UL scanf
reads characters, interprets
them according to a format, and stores the results in its arguments.
Each routine expects as arguments
a control string
.UL format ,
and a set of arguments,
.I
each of which must be a pointer,
.R
indicating where the converted input should be stored.
.if t .sp .4v
.UL scanf
returns as its value the number of successfully matched and assigned input
items.
This can be used to decide how many input items were found.
On end of file,
.UL EOF
is returned; note that this is different
from 0, which means that the next input character does not
match what was called for in the control string.
.nr PD .4v
.LP
.UL fread(ptr,\ sizeof(*ptr),\ nitems,\ ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
reads
.UL nitems
of data beginning at
.UL ptr
from file
.UL ioptr .
No advance notification
that binary I/O is being done is required;
when, for portability reasons,
it becomes required, it will be done
by adding an additional character to the mode-string on the
.UL fopen
call.
.nr PD .4v
.LP
.UL fwrite(ptr,\ sizeof(*ptr),\ nitems,\ ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
Like
.UL fread ,
but in the other direction.
.nr PD .4v
.LP
.UL rewind(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
rewinds the stream
named by
.UL ioptr .
It is not very useful except on input,
since a rewound output file is still open only for output.
.nr PD .4v
.LP
.UL system(string)\ char\ *string;
.nr PD 0
.IP
.br
The
.UL string
is executed by the shell as if typed at the terminal.
.nr PD .4v
.LP
.UL getw(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
returns the next word from the input stream named by
.UL ioptr .
.UL EOF
is returned on end-of-file or error,
but since this a perfectly good
integer
.UL feof
and
.UL ferror
should be used.
A ``word'' is 16 bits on the
.UC PDP-11.
.nr PD .4v
.LP
.UL putw(w,\ ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
writes the integer
.UL w
on the named output stream.
.nr PD .4v
.LP
.UL setbuf(ioptr,\ buf)\ FILE\ *ioptr;\ char\ *buf;
.nr PD 0
.IP
.br
.UL setbuf
may be used after a stream has been opened
but before I/O has started.
If
.UL buf
is
.UL NULL ,
the stream will be unbuffered.
Otherwise the buffer supplied will be used.
It must be a character array of sufficient size:
.P1
char	buf[BUFSIZ];
.P2
.nr PD .4v
.LP
.UL fileno(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
returns the integer file descriptor associated with the file.
.nr PD .4v
.LP
.UL fseek(ioptr,\ offset,\ ptrname)\ FILE\ *ioptr;\ long\ offset;
.nr PD 0
.IP
.br
The location of the next byte in the stream
named by
.UL ioptr
is adjusted.
.UL offset
is a long integer.
If
.UL ptrname
is 0, the offset is measured from the beginning of the file;
if
.UL ptrname
is 1, the offset is measured from the current read or
write pointer;
if
.UL ptrname
is 2, the offset is measured from the end of the file.
The routine accounts properly for any buffering.
(When this routine is used on
.UC UNIX \& non-
systems,
the offset must be a value returned from
.UL ftell
and the ptrname must be 0).
.ne 3
.nr PD .4v
.LP
.UL long\ ftell(ioptr)\ FILE\ *ioptr;
.nr PD 0
.IP
.br
The byte offset, measured from the beginning of the file,
associated with the named stream is returned.
Any buffering is properly accounted for.
(On
.UC UNIX \& non-
systems the value of this call is useful only
for handing to
.UL fseek ,
so as to position the file to the same place it was when
.UL ftell
was called.)
.nr PD .4v
.LP
.UL getpw(uid,\ buf)\ char\ *buf;
.nr PD 0
.IP
.br
The password file is searched for the given integer user ID.
If an appropriate line is found, it is copied into
the character array
.UL buf ,
and 0 is returned.
If no line is found corresponding to the user ID
then 1 is returned.
.nr PD .4v
.LP
.UL char\ *malloc(num);
.nr PD 0
.IP
.br
allocates
.UL num
bytes.
The pointer returned is sufficiently well aligned to be usable for any purpose.
.UL NULL
is returned if no space is available.
.nr PD .4v
.LP
.UL char\ *calloc(num,\ size);
.nr PD 0
.IP
.br
allocates space for
.UL num
items each of size
.UL size .
The space is guaranteed to be set to 0 and the pointer is
sufficiently well aligned to be usable for any purpose.
.UL NULL
is returned if no space is available .
.nr PD .4v
.LP
.UL cfree(ptr)\ char\ *ptr;
.nr PD 0
.IP
.br
Space is returned to the pool used by
.UL calloc .
Disorder can be expected if the pointer was not obtained
from
.UL calloc .
.nr PD .4v
.LP
The following are macros whose definitions may be obtained by including
.UL <ctype.h> .
.nr PD .4v
.LP
.UL isalpha(c)
returns non-zero if the argument is alphabetic.
.nr PD .4v
.LP
.UL isupper(c)
returns non-zero if the argument is upper-case alphabetic.
.nr PD .4v
.LP
.UL islower(c)
returns non-zero if the argument is lower-case alphabetic.
.nr PD .4v
.LP
.UL isdigit(c)
returns non-zero if the argument is a digit.
.nr PD .4v
.LP
.UL isspace(c)
returns non-zero if the argument is a spacing character:
tab, newline, carriage return, vertical tab,
form feed, space.
.nr PD .4v
.LP
.UL ispunct(c)
returns non-zero if the argument is
any punctuation character, i.e., not a space, letter,
digit or control character.
.nr PD .4v
.LP
.UL isalnum(c)
returns non-zero if the argument is a letter or a digit.
.nr PD .4v
.LP
.UL isprint(c)
returns non-zero if the argument is printable \(em
a letter, digit, or punctuation character.
.nr PD .4v
.LP
.UL iscntrl(c)
returns non-zero if the argument is a control character.
.nr PD .4v
.LP
.UL isascii(c)
returns non-zero if the argument is an ascii character, i.e., less than octal 0200.
.nr PD .4v
.LP
.UL toupper(c)
returns the upper-case character corresponding to the lower-case
letter
.UL c.
.nr PD .4v
.LP
.UL tolower(c)
returns the lower-case character corresponding to the upper-case
letter
.UL c .