BSD 4_4 release

[unix-history] / usr / src / lib / libc / stdio / printf.3

diff --git a/usr/src/lib/libc/stdio/printf.3 b/usr/src/lib/libc/stdio/printf.3
index f75a208..70f8b99 100644 (file)
--- a/usr/src/lib/libc/stdio/printf.3
+++ b/usr/src/lib/libc/stdio/printf.3
@@ -1,478 +1,638 @@
-.\"    @(#)printf.3    6.7 (Berkeley) 4/14/89
+.\" Copyright (c) 1990, 1991, 1993
+.\"    The Regents of the University of California.  All rights reserved.

 .\"
 .\"

-.TH PRINTF 3 "October 22, 1987"
-.AT 3
-.SH NAME
-fprintf, printf, sprintf, vprintf, vfprintf, vsprintf - formatted
-output conversion
-.SH SYNOPSIS
-.B #include <stdio.h>
-.PP
-.B printf(format
-.RB [ ,
-arg ] ...
-.B )
-.br
-.B char *format;
-.PP
-.B fprintf(stream, format
-.RB [ ,
-arg ] ...
-.B )
-.br
-.SM
-.B FILE
-.B *stream;
-.br
-.B char *format;
-.PP
-.B sprintf(s, format
-.RB [ ,
-arg ] ...
-.B )
-.br
-.B char *s, *format;
-.PP
-.B #include <varargs.h>
-.br
-.B vprintf(format, args)
-.br
-.B char *format;
-.br
-.B va_list args;
-.PP
-.B vfprintf(stream, format, args)
-.br
-.B FILE *stream;
-.br
-.B char *format;
-.br
-.B va_list args;
-.PP
-.B vsprintf(s, format, args)
-.br
-.B char *s, *format;
-.br
-.B va_list args;
-.SH DESCRIPTION
-.I Printf
-and
-.I vprintf
-place output on the standard output stream
-.BR stdout .
-.I Fprintf
+.\" This code is derived from software contributed to Berkeley by
+.\" Chris Torek and the American National Standards Committee X3,
+.\" on Information Processing Systems.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"    This product includes software developed by the University of
+.\"    California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)printf.3   8.1 (Berkeley) 6/4/93
+.\"
+.Dd June 4, 1993
+.Dt PRINTF 3
+.Os
+.Sh NAME
+.Nm printf ,
+.Nm fprintf ,
+.Nm sprintf ,
+.Nm snprintf ,
+.Nm vprintf ,
+.Nm vfprintf,
+.Nm vsprintf ,
+.Nm vsnprintf
+.Nd formatted output conversion
+.Sh SYNOPSIS
+.Fd #include <stdio.h>
+.Ft int
+.Fn printf "const char *format" ...
+.Ft int
+.Fn fprintf "FILE *stream" "const char *format" ...
+.Ft int
+.Fn sprintf "char *str" "const char *format" ...
+.Ft int
+.Fn snprintf "char *str" "size_t size" "const char *format" ...
+.\" .Ft int
+.\" .Fn smprintf "const char *format" ...
+.Fd #include <stdarg.h>
+.Ft int
+.Fn vprintf "const char *format" "va_list ap"
+.Ft int
+.Fn vfprintf "FILE *stream" "const char *format" "va_list ap"
+.Ft int
+.Fn vsprintf "char *str" "char *format" "va_list ap"
+.Ft int
+.Fn vsnprintf "char *str" "size_t size" "const char *format" "va_list ap"
+.\" .Ft int
+.\" .Fn vsmprintf "const char *format" "va_list ap"
+.Sh DESCRIPTION
+The
+.Fn printf
+family of functions produces output according to a
+.Fa format
+as described below.
+.Fn Printf

 and
 and

-.I vfprintf
-place output on the named output
-.IR stream .
-.I Sprintf
+.Fn vprintf
+write output to
+.Em stdout,
+the standard output stream;
+.Fn fprintf

 and
 and

-.I vsprintf
-copy into the string
-.IR s ,
-followed by the character `\e0'.
-.IR Printf ,
-.IR fprintf ,
+.Fn vfprintf
+write output to the given output
+.Fa stream ;
+.Fn sprintf ,
+.Fn snprintf ,
+.Fn vsprintf ,

 and
 and

-.I sprintf
-take variadic argument lists directly, while
-.IR vprintf ,
-.IR vfprintf ,
+.Fn vsnprintf
+write to the character string
+.Fa str .
+.\" .IR str ;
+.\" and
+.\" .I smprintf
+.\" and
+.\" .I vsmprintf
+.\" dynamically allocate a new string with
+.\" .IR malloc .
+These functions write the output under the control of a
+.Fa format
+string that specifies how subsequent arguments
+(or arguments accessed via the variable-length argument facilities of
+.Xr stdarg 3 )
+are converted for output.
+.\" Except for
+.\" .I smprintf
+.\" and
+.\" .IR vsmprintf ,
+.\" all of these functions return
+These functions return
+the number of characters printed
+(not including the trailing
+.Ql \e0
+used to end output to strings).
+.\" .I Smprintf
+.\" and
+.\" .I vsmprintf
+.\" return a pointer to a string of an appropriate length;
+.\" this pointer should be passed to
+.\" .I free
+.\" to release the associated storage
+.\" when it is no longer needed.
+.\" If sufficient space is not avaliable,
+.\" .I smprintf
+.\" and
+.\" .I vsmprintf
+.\" will return
+.\" .SM
+.\" .BR
+.Fn Snprintf

 and
 and

-.I vsprintf
-use the variable-length argument facilities of
-.IR varargs (3)
-and hence may be called indirectly (see examples).
-.PP
-Each function converts, formats, and prints its arguments after the
-.I format
-under control of the
-.I format
-argument; each returns the the total number of characters printed (not
-including the trailing `\e0' in
-.I sprintf
+.Fn vsnprintf
+will write at most
+.Fa size Ns \-1
+of the characters printed into the output string
+(the
+.Fa size Ns 'th
+character then gets the terminating
+.Ql \e0 ) ;
+if the return value is greater than or equal to the
+.Fa size
+argument, the string was too short
+and some of the printed characters were discarded.
+.Fn Sprintf

 and
 and

-.IR vsprintf ).
-.I Format
-is a character string which contains two types of objects: plain characters,
-which are simply copied to the output stream, and conversion specifications,
-each of which causes conversion and printing of the next successive
-.IR arg .
-.PP
-Each conversion specification is introduced by the percent character (``%'').
-The remainder of the conversion specification includes, in the following
-order,
-.TP
-.B \(bu
+.Fn vsprintf
+effectively assume an infinite
+.Fa size .
+.Pp
+The format string is composed of zero or more directives:
+ordinary
+.\" multibyte
+characters (not
+.Cm % ) ,
+which are copied unchanged to the output stream;
+and conversion specifications, each of which results
+in fetching zero or more subsequent arguments.
+Each conversion specification is introduced by
+the character
+.Cm % .
+The arguments must correspond properly (after type promotion)
+with the conversion specifier.
+After the
+.Cm % ,
+the following appear in sequence:
+.Bl -bullet
+.It

 Zero or more of the following flags:
 Zero or more of the following flags:

-.RS
-.TP
-.B \(bu
-a `#' character
+.Bl -hyphen
+.It
+A
+.Cm #
+character

 specifying that the value should be converted to an ``alternate form''.
 For 
 specifying that the value should be converted to an ``alternate form''.
 For 

-.BR c ,
-.BR d ,
-.BR i ,
-.BR n ,
-.BR p ,
-.BR s ,
+.Cm c ,
+.Cm d ,
+.Cm i ,
+.Cm n ,
+.Cm p ,
+.Cm s ,

 and
 and

-.BR u ,
+.Cm u ,

 conversions, this option has no effect.
 For 
 conversions, this option has no effect.
 For 

-.B o
+.Cm o

 conversions, the precision of the number is increased to force the first
 character of the output string to a zero (except if a zero value is printed
 with an explicit precision of zero).
 For
 conversions, the precision of the number is increased to force the first
 character of the output string to a zero (except if a zero value is printed
 with an explicit precision of zero).
 For

-.B x
+.Cm x

 and
 and

-.B X
+.Cm X

 conversions, a non-zero result has the string
 conversions, a non-zero result has the string

-.B 0x
+.Ql 0x

 (or
 (or

-.B 0X
+.Ql 0X

 for
 for

-.B X
+.Cm X

 conversions) prepended to it.
 For
 conversions) prepended to it.
 For

-.BR e ,
-.BR E ,
-.BR f ,
-.BR g ,
+.Cm e ,
+.Cm E ,
+.Cm f ,
+.Cm g ,

 and
 and

-.BR G ,
+.Cm G ,

 conversions, the result will always contain a decimal point, even if no
 digits follow it (normally, a decimal point appears in the results of
 those conversions only if a digit follows).
 For
 conversions, the result will always contain a decimal point, even if no
 digits follow it (normally, a decimal point appears in the results of
 those conversions only if a digit follows).
 For

-.B g
+.Cm g

 and
 and

-.B G
+.Cm G

 conversions, trailing zeros are not removed from the result as they
 would otherwise be.
 conversions, trailing zeros are not removed from the result as they
 would otherwise be.

-.TP
-.B \(bu
-A zero ``0'' character specifying zero padding.
+.It
+A zero
+.Sq Cm \&0
+character specifying zero padding.

 For all conversions except
 For all conversions except

-.BR n ,
+.Cm n ,

 the converted value is padded on the left with zeros rather than blanks.
 the converted value is padded on the left with zeros rather than blanks.

-If a precision is given with a numeric conversion (
-.BR d ,
-.BR i ,
-.BR o ,
-.BR u ,
-.BR i ,
-.BR x ,
+If a precision is given with a numeric conversion
+.Pf ( Mc d ,
+.Cm i ,
+.Cm o ,
+.Cm u ,
+.Cm i ,
+.Cm x ,

 and
 and

-.BR X ),
-the ``0'' flag is ignored.
-.TP
-.B \(bu
-A minus sign (``-'') specifying left adjustment of the converted value
-in the indicated field.
+.Cm X ) ,
+the
+.Sq Cm \&0
+flag is ignored.
+.It
+A negative field width flag
+.Sq Cm \-
+indicates the converted value is to be left adjusted on the field boundary.

 Except for
 Except for

-.B n
+.Cm n

 conversions, the converted value is padded on the right with blanks,
 rather than on the left with blanks or zeros.
 conversions, the converted value is padded on the right with blanks,
 rather than on the left with blanks or zeros.

-A ``-'' overrides a ``0'' if both are given.
-.TP
-.B \(bu
+A
+.Sq Cm \-
+overrides a
+.Sq Cm \&0
+if both are given.
+.It

 A space, specifying that a blank should be left before a positive number
 A space, specifying that a blank should be left before a positive number

-produced by a signed conversion (
-.BR d ,
-.BR e ,
-.BR E ,
-.BR f ,
-.BR g ,
-.BR G ,
+produced by a signed conversion
+.Pf ( Cm d ,
+.Cm e ,
+.Cm E ,
+.Cm f ,
+.Cm g ,
+.Cm G ,

 or
 or

-.BR i ).
-.TP
-.B \(bu
-a `+' character specifying that a sign always be placed before a
+.Cm i ) .
+.It
+A
+.Sq Cm +
+character specifying that a sign always be placed before a

 number produced by a signed conversion.
 number produced by a signed conversion.

-A ``+'' overrides a space if both are used.
-.RE
-.TP
-.B \(bu
-An optional digit string specifying a field width.
+A
+.Sq Cm +
+overrides a space if both are used.
+.El
+.It
+An optional decimal digit string specifying a minimum field width.

 If the converted value has fewer characters than the field width, it will
 If the converted value has fewer characters than the field width, it will

-be padded on the left (or right, if the left-adjustment flag is used) to
-make up the field width.
-.TP
-.B \(bu
-An optional precision, in the form of a period (``.'') followed by an
+be padded with spaces on the left (or right, if the left-adjustment
+flag has been given) to fill out
+the field width.
+.It
+An optional precision, in the form of a period
+.Sq Cm \&.
+followed by an

 optional digit string.  If the digit string is omitted, the precision
 is taken as zero.  This gives the minimum number of digits to appear for
 optional digit string.  If the digit string is omitted, the precision
 is taken as zero.  This gives the minimum number of digits to appear for

-.BR d ,
-.BR i ,
-.BR o ,
-.BR u ,
-.BR x ,
+.Cm d ,
+.Cm i ,
+.Cm o ,
+.Cm u ,
+.Cm x ,

 and
 and

-.B X
-conversions, the number of digits to appear after the decimal point for
-.BR e ,
-.BR E ,
+.Cm X
+conversions, the number of digits to appear after the decimal-point for
+.Cm e ,
+.Cm E ,

 and
 and

-.B f
+.Cm f

 conversions, the maximum number of significant digits for
 conversions, the maximum number of significant digits for

-.B g
+.Cm g

 and
 and

-.B G
+.Cm G

 conversions, or the maximum number of characters to be printed from a
 string for
 conversions, or the maximum number of characters to be printed from a
 string for

-.B s
+.Cm s

 conversions.
 conversions.

-.TP
-.B \(bu
-The character
-.BR h ,
+.It
+The optional character
+.Cm h ,

 specifying that a following
 specifying that a following

-.BR d ,
-.BR i ,
-.BR o ,
-.BR u ,
-.BR x ,
+.Cm d ,
+.Cm i ,
+.Cm o ,
+.Cm u ,
+.Cm x ,

 or
 or

-.B X
+.Cm X

 conversion corresponds to a
 conversion corresponds to a

-.B "short int"
+.Em short int

 or
 or

-.B "unsigned short int"
+.Em unsigned short int

 argument, or that a following
 argument, or that a following

-.B n
+.Cm n

 conversion corresponds to a pointer to a
 conversion corresponds to a pointer to a

-.B "short int"
+.Em short int

 argument.
 argument.

-.TP
-.B \(bu
-the character
-.B l
+.It
+The optional character
+.Cm l

 (ell) specifying that a following
 (ell) specifying that a following

-.BR d ,
-.BR i ,
-.BR o ,
-.BR u ,
-.BR x ,
+.Cm d ,
+.Cm i ,
+.Cm o ,
+.Cm u ,
+.Cm x ,
+or
+.Cm X
+conversion applies to a pointer to a
+.Em long int
+or
+.Em unsigned long int
+argument, or that a following
+.Cm n
+conversion corresponds to a pointer to a
+.Em long int
+argument.
+.It
+The optional character
+.Cm q ,
+specifying that a following
+.Cm d ,
+.Cm i ,
+.Cm o ,
+.Cm u ,
+.Cm x ,

 or
 or

-.B X
+.Cm X

 conversion corresponds to a
 conversion corresponds to a

-.B "long int"
+.Em quad int

 or
 or

-.B "unsigned long int"
+.Em unsigned quad int

 argument, or that a following
 argument, or that a following

-.B n
+.Cm n

 conversion corresponds to a pointer to a
 conversion corresponds to a pointer to a

-.B "long int"
+.Em quad int

 argument.
 argument.

-.TP
-.B \(bu
+.It

 The character
 The character

-.B L
+.Cm L

 specifying that a following
 specifying that a following

-.BR e ,
-.BR E ,
-.BR f ,
-.BR g ,
+.Cm e ,
+.Cm E ,
+.Cm f ,
+.Cm g ,

 or
 or

-.B G
+.Cm G

 conversion corresponds to a
 conversion corresponds to a

-.B "long double"
+.Em long double

 argument (but note that long double values are not currently supported
 argument (but note that long double values are not currently supported

-by the \s-2VAX\s0 and Tahoe compilers).
-.TP
-.B \(bu
-A character which indicates the type of conversion to be applied.
-.PP
-A field width or precision may be an asterisk (``*'') instead of a
+by the
+.Tn VAX
+and
+.Tn Tahoe
+compilers).
+.It
+A character that specifies the type of conversion to be applied.
+.El
+.Pp
+A field width or precision, or both, may be indicated by
+an asterisk
+.Ql *
+instead of a

 digit string.
 digit string.

-In this case an
-.B int
-argument supplies the value.
+In this case, an
+.Em int
+argument supplies the field width or precision.

 A negative field width is treated as a left adjustment flag followed by a
 positive field width; a negative precision is treated as though it were
 missing.
 A negative field width is treated as a left adjustment flag followed by a
 positive field width; a negative precision is treated as though it were
 missing.

-.PP
-The conversion characters and their meanings are:
-.TP
-.B diouxX
+.Pp
+The conversion specifiers and their meanings are:
+.Bl -tag -width "diouxX"
+.It Cm diouxX

 The
 The

-.B int
+.Em int

 (or appropriate variant) argument is converted to signed decimal
 (or appropriate variant) argument is converted to signed decimal

-.RB ( d " and " i ),
+.Pf ( Cm d
+and
+.Cm i ) ,

 unsigned octal
 unsigned octal

-.RB ( o ),
+.Pq Cm o ,

 unsigned decimal
 unsigned decimal

-.RB ( u ),
+.Pq Cm u ,

 or unsigned hexadecimal
 or unsigned hexadecimal

-.RB ( x " and " X )
-notation respectively.  The letters
-.B abcdef
+.Pf ( Cm x
+and
+.Cm X )
+notation.  The letters
+.Cm abcdef

 are used for
 are used for

-.B x
+.Cm x

 conversions; the letters
 conversions; the letters

-.B ABCDEF
+.Cm ABCDEF

 are used for
 are used for

-.B X
+.m X

 conversions.
 The precision, if any, gives the minimum number of digits that must
 appear; if the converted value requires fewer digits, it is padded on
 the left with zeros.
 conversions.
 The precision, if any, gives the minimum number of digits that must
 appear; if the converted value requires fewer digits, it is padded on
 the left with zeros.

-.TP
-.B DOU
+.It Cm DOU

 The
 The

-.B "long int"
+.Em long int

 argument is converted to signed decimal, unsigned octal, or unsigned
 decimal, as if the format had been
 argument is converted to signed decimal, unsigned octal, or unsigned
 decimal, as if the format had been

-.BR ld ,
-.BR lo ,
+.Cm ld ,
+.Cm lo ,

 or
 or

-.B lu
+.Cm lu

 respectively.
 These conversion characters are deprecated, and will eventually disappear.
 respectively.
 These conversion characters are deprecated, and will eventually disappear.

-.TP 8
-.B eE
+.It Cm eE

 The
 The

-.B double
+.Em double

 argument is rounded and converted in the style
 argument is rounded and converted in the style

-`[\fB\-\fR]d\fB.\fRddd\fBe\fR\(+-dd' where there is one digit before the
-decimal point and the number after is equal to the precision specification
-for the argument.
-If the precision is missing, 6 digits are given; if the precision is
-explicitly zero, no decimal point appears.
+.Sm off
+.Pf [\-]d Cm \&. No ddd Cm e No \\*(Pmdd
+.Sm on
+where there is one digit before the
+decimal-point character
+and the number of digits after it is equal to the precision;
+if the precision is missing,
+it is taken as 6; if the precision is
+zero, no decimal-point character appears.

 An
 An

-.B E
+.Cm E

 conversion uses the letter
 conversion uses the letter

-.B E
+.Cm E

 (rather than
 (rather than

-.BR e )
+.Cm e )

 to introduce the exponent.
 The exponent always contains at least two digits; if the value is zero,
 the exponent is 00.
 to introduce the exponent.
 The exponent always contains at least two digits; if the value is zero,
 the exponent is 00.

-.TP 8
-.B f
+.It Cm f

 The
 The

-.B double
+.Em double

 argument is rounded and converted to decimal notation in the style
 argument is rounded and converted to decimal notation in the style

-`[\fB\-\fR]ddd.ddd' where the number of digits after the decimal point
-is equal to the precision.
-If the precision is missing, 6 digits are given; if the precision is
-explicitly 0, no digits and no decimal point are printed.
+.Sm off
+.Pf [-]ddd Cm \&. No ddd ,
+.Sm on
+where the number of digits after the decimal-point character
+is equal to the precision specification.
+If the precision is missing, it is taken as 6; if the precision is
+explicitly zero, no decimal-point character appears.

 If a decimal point appears, at least one digit appears before it.
 If a decimal point appears, at least one digit appears before it.

-.TP 8
-.B g
+.It Cm g

 The
 The

-.B double
-argument is printed in style
-.B f
+.Em double
+argument is converted in style
+.Cm f

 or
 or

-.B e
+.Cm e

 (or
 (or

-.B E
+.Cm E

 for
 for

-.B G
+.Cm G

 conversions).
 The precision specifies the number of significant digits.
 If the precision is missing, 6 digits are given; if the precision is zero,
 it is treated as 1.
 Style
 conversions).
 The precision specifies the number of significant digits.
 If the precision is missing, 6 digits are given; if the precision is zero,
 it is treated as 1.
 Style

-.B e
+.Cm e

 is used if the exponent from its conversion is less than -4 or greater than
 or equal to the precision.
 Trailing zeros are removed from the fractional part of the result; a
 decimal point appears only if it is followed by at least one digit.
 is used if the exponent from its conversion is less than -4 or greater than
 or equal to the precision.
 Trailing zeros are removed from the fractional part of the result; a
 decimal point appears only if it is followed by at least one digit.

-.TP 8
-.B c
+.It Cm c

 The
 The

-.B int
+.Em int

 argument is converted to an
 argument is converted to an

-.B "unsigned char",
-and the resulting character is printed.
-.TP 8
-.B s
+.Em unsigned char ,
+and the resulting character is written.
+.It Cm s

 The
 The

-.B "char *"
-argument is taken to be a string (character pointer).
-Characters from the string are printed until a null character is reached,
-or until the number of characters indicated by the precision have been
-printed, whichever occurs first; if a precision is given, no null character
-need be present.
-.TP 8
-.B p
+.Dq Em char *
+argument is expected to be a pointer to an array of character type (pointer
+to a string).
+Characters from the array are written up to (but not including)
+a terminating
+.Dv NUL
+character;
+if a precision is specified, no more than the number specified are
+written.
+If a precision is given, no null character
+need be present; if the precision is not specified, or is greater than
+the size of the array, the array must contain a terminating
+.Dv NUL
+character.
+.It Cm p

 The
 The

-.B "void *"
-pointer argument is printed in hexadecimal (as if by ``%x'' or ``%lx'').
-.TP 8
-.B n
+.Dq Em void *
+pointer argument is printed in hexadecimal (as if by
+.Ql %#x
+or
+.Ql %#lx ) .
+.It Cm n

 The number of characters written so far is stored into the
 integer indicated by the
 The number of characters written so far is stored into the
 integer indicated by the

-.B "int *"
+.Dq Em int *

 (or variant) pointer argument.
 No argument is converted.
 (or variant) pointer argument.
 No argument is converted.

-.TP 8
-.B %
-Prints a `%'; no argument is converted.
-.PP
+.It Cm %
+A
+.Ql %
+is written. No argument is converted. The complete conversion specification
+is
+.Ql %% .
+.El
+.Pp

 In no case does a non-existent or small field width cause truncation of
 a field; if the result of a conversion is wider than the field width, the
 In no case does a non-existent or small field width cause truncation of
 a field; if the result of a conversion is wider than the field width, the

-field is expanded to contain it.
-Similarly, padding takes place only if the specified field width exceeds
-the actual width.
-.PP
-.SH EXAMPLES
+field is expanded to contain the conversion result.
+.Pp
+.Sh EXAMPLES

 .br
 To print a date and time in the form `Sunday, July 3, 10:02',
 where
 .br
 To print a date and time in the form `Sunday, July 3, 10:02',
 where

-.I weekday
+.Em weekday

 and
 and

-.I month
-are pointers to null-terminated strings:
-.RS
-.HP
-.nh
-printf("%s, %s %d, %02d:%.2d", weekday, month, day, hour, min);
-.RE
-.hy
-.PP
-To print
-.if n pi
-.if t \(*p
-to 5 decimals:
-.IP
-printf("pi = %.5f", 4*atan(1.0));
-.PP
+.Em month
+are pointers to strings:
+.Bd -literal -offset indent
+#include <stdio.h>
+fprintf(stdout, "%s, %s %d, %.2d:%.2d\en",
+       weekday, month, day, hour, min);
+.Ed
+.Pp
+To print \*(Pi
+to five decimal places:
+.Bd -literal -offset indent
+#include <math.h>
+#include <stdio.h>
+fprintf(stdout, "pi = %.5f\en", 4 * atan(1.0));
+.Ed
+.Pp

 To allocate a 128 byte string and print into it:
 To allocate a 128 byte string and print into it:

-.RS
-.nf
-.ta 1i 2i
-.sp
+.Bd -literal -offset indent

 #include <stdio.h>
 #include <stdio.h>

-#include <varargs.h>
-char *newfmt(va_alist)
-       va_dcl
+#include <stdlib.h>
+#include <stdarg.h>
+char *newfmt(const char *fmt, ...)

 {
 {

-       char *p, *malloc(), fmt;
-       va_list ap;
-       if ((p = malloc(128)) == NULL)
-               return (NULL);
-       va_start(ap);
-       fmt = va_arg(ap, char *);
-       (void) vsprintf(p, fmt, ap);
-       va_end(ap);
-       return (p);
+               char *p;
+               va_list ap;
+               if ((p = malloc(128)) == NULL)
+                       return (NULL);
+               va_start(ap, fmt);
+               (void) vsnprintf(p, 128, fmt, ap);
+               va_end(ap);
+               return (p);

 }
 }

-.RE
-.fi
-.SH "SEE ALSO"
-putc(3), scanf(3)
-.SH BUGS
-The conversion formats ``%D'', ``%O'', and ``%U'' are not standard and
+.Ed
+.Sh SEE ALSO
+.Xr printf 1 ,
+.Xr scanf 3
+.Sh STANDARDS
+The
+.Fn fprintf ,
+.Fn printf ,
+.Fn sprintf ,
+.Fn vprintf ,
+.Fn vfprintf ,
+and
+.Fn vsprintf
+functions
+conform to
+.St -ansiC .
+.Sh HISTORY
+The functions
+.Fn snprintf
+and
+.Fn vsnprintf
+are new to this release.
+.Sh BUGS
+The conversion formats
+.Cm \&%D ,
+.Cm \&%O ,
+and
+.Cm %U
+are not standard and

 are provided only for backward compatibility.
 are provided only for backward compatibility.

-The effect of padding the ``%p'' format with zeros (either by the ``0''
+The effect of padding the
+.Cm %p
+format with zeros (either by the
+.Sq Cm 0

 flag or by specifying a precision), and the benign effect (i.e., none)
 flag or by specifying a precision), and the benign effect (i.e., none)

-of the ``#'' flag on ``%n'' and ``%p'' conversions, as well as other
-nonsensical combinations such as ``%Ld'', are not standard; such combinations
+of the
+.Sq Cm #
+flag on
+.Cm %n
+and
+.Cm %p
+conversions, as well as other
+nonsensical combinations such as
+.Cm %Ld ,
+are not standard; such combinations

 should be avoided.
 should be avoided.

+.Pp
+Because
+.Fn sprintf
+and
+.Fn vsprintf
+assume an infinitely long string,
+callers must be careful not to overflow the actual space;
+this is often impossible to assure.
+For safety, programmers should use the
+.Fn snprintf
+interface instead.
+Unfortunately, this interface is not portable.