265 lines
6.1 KiB
Groff
265 lines
6.1 KiB
Groff
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.\" @(#)printf.3s 6.3 (Berkeley) 6/5/86
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.\"
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.TH PRINTF 3 "June 5, 1986"
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.AT 3
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.SH NAME
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printf, fprintf, sprintf, snprintf, vprintf, vfprintf, vsprintf, vsnprintf \- formatted output conversion
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.SH SYNOPSIS
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.nf
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.ft B
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#include <sys/types.h>
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#include <stdio.h>
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#include <stdarg.h>
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int printf(const char *\fIformat\fP \fR[\fP, \fIarg\fP\fR] ...\fP);
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int fprintf(FILE *\fIstream\fP, const char *\fIformat\fP \fR[\fP, \fIarg\fP\fR] ...\fP);
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int sprintf(char *\fIs\fP, const char *\fIformat\fP \fR[\fP, \fIarg\fP\fR] ...\fP);
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int snprintf(char *\fIs\fP, size_t \fIn\fP, const char *\fIformat\fP \fR[\fP, \fIarg\fP\fR] ...\fP);
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int vprintf(const char *\fIformat\fP, va_list \fIargs\fP);
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int vfprintf(FILE *\fIstream\fP, const char *\fIformat\fP, va_list \fIargs\fP);
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int vsprintf(char *\fIs\fP, const char *\fIformat\fP, va_list \fIargs\fP);
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int vsnprintf(char *\fIs\fP, size_t \fIn\fP, const char *\fIformat\fP, va_list \fIargs\fP);
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.ft R
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.fi
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.SH DESCRIPTION
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.B Printf
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places output on the standard output stream
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.BR stdout .
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.B Fprintf
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places output on the named output
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.IR stream .
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.B Sprintf
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places `output' in the string
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.IR s ,
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followed by the character `\e0'.
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.B Snprintf
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(Minix-vmd only)
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is like
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.B sprintf
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except that no more than
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.IR n \-1
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characters are written to
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.I s
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followed by a `\e0'.
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.PP
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The
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.B v*printf
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functions can be used to make functions like the first four by using the
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.BR stdarg (3)
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method to process the argument.
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.PP
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Each of these functions converts, formats, and prints its arguments after
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the first under control of the first argument.
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The first argument is a character string which contains two types of objects:
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plain characters, which are simply copied to the output stream,
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and conversion specifications, each of which causes conversion and printing
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of the next successive
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.IR arg .
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.PP
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Each conversion specification is introduced by the character
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.BR % .
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The remainder of the conversion specification includes
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in the following order
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.TP
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\(bu
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Zero or more of following flags:
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.RS
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.TP
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\(bu
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a `#' character
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specifying that the value should be converted to an ``alternate form''.
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For
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.BR c ,
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.BR d ,
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.BR s ,
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and
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.BR u
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conversions, this option has no effect. For
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.B o
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conversions, the precision of the number is increased to force the first
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character of the output string to a zero. For
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.BR x ( X )
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conversion, a non-zero result has the string
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.BR 0x ( 0X )
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prepended to it. For
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.BR e ,
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.BR E ,
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.BR f ,
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.BR g ,
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and
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.BR G
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conversions, the result will always contain a decimal point, even if no
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digits follow the point (normally, a decimal point only appears in the
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results of those conversions if a digit follows the decimal point). For
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.B g
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and
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.B G
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conversions, trailing zeros are not removed from the result as they
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would otherwise be.
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.TP
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\(bu
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a minus sign `\-' which specifies
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.I "left adjustment"
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of the converted value in the indicated field;
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.TP
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\(bu
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a `+' character specifying that there should always be
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a sign placed before the number when using signed conversions.
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.TP
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\(bu
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a space specifying that a blank should be left before a positive number
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during a signed conversion. A `+' overrides a space if both are used.
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.RE
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.TP
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\(bu
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an optional digit string specifying a
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.I "field width;"
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if the converted value has fewer characters than the field width
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it will be blank-padded on the left (or right,
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if the left-adjustment indicator has been given) to make up the field width;
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if the field width begins with a zero,
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zero-padding will be done instead of blank-padding;
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.TP
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\(bu
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an optional period
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.RB ` . '
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which serves to separate the field width from the next digit string;
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.TP
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\(bu
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an optional digit string specifying a
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.I precision
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which specifies the number of digits to appear after the
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decimal point, for e- and f-conversion, or the maximum number of characters
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to be printed from a string;
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.TP
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\(bu
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the character
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.B l
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specifying that a following
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.BR d ,
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.BR o ,
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.BR x ,
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or
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.B u
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corresponds to a long integer
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.IR arg .
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.TP
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\(bu
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a character which indicates the type of
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conversion to be applied.
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.PP
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A field width or precision may be `*' instead of a digit string.
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In this case an integer
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.I arg
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supplies
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the field width or precision.
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.PP
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The conversion characters
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and their meanings are
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.TP
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.B dox
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The integer
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.I arg
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is converted to decimal, octal, or
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hexadecimal notation respectively.
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.TP
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.B X
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Like
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.BR x ,
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but use upper case instead of lower case.
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.TP
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.B f
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The float or double
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.I arg
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is converted to decimal notation
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in the style `[\fB\-\fR]ddd.ddd'
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where the number of d's after the decimal point
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is equal to the precision specification
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for the argument.
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If the precision
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is missing,
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6 digits are given;
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if the precision is explicitly 0, no digits and
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no decimal point are printed.
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.TP
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.B e
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The float or double
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.I arg
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is converted in the style
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`[\fB\-\fR]d\fB.\fRddd\fBe\fR\(+-dd'
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where there is one digit before the decimal point and
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the number after is equal to the
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precision specification for the argument;
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when the precision is missing,
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6 digits are produced.
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.TP
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.B g
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The float or double
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.I arg
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is printed in style
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.BR d ,
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in style
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.BR f ,
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or in
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style
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.BR e ,
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whichever gives full precision in minimum space.
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.TP
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.B c
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The character
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.I arg
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is printed.
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.TP
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.B s
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.I Arg
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is taken to be a string (character pointer)
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and characters from the string are printed until
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a null character or until
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the number of characters indicated by the precision
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specification is reached;
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however if the precision is 0 or missing
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all characters up to a null are printed.
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.TP
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.B u
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The unsigned integer
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.I arg
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is converted to decimal
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and printed.
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.TP
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.B %
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Print a `%'; no argument is converted.
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.PP
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In no case does a non-existent or small field width
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cause truncation of a field;
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padding takes place only if the specified field
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width exceeds the actual width.
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Characters generated by
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.B printf
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are printed by
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.BR putc (3).
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.PP
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.B Examples
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.br
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To print a date and time in the form `Sunday, July 3, 10:02',
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where
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.I weekday
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and
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.I month
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are pointers to null-terminated strings:
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.PP
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.RS
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printf("%s, %s %d, %02d:%02d", weekday, month, day, hour, min);
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.RE
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.PP
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To print
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.if n pi
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.if t \(*p
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to 5 decimals:
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.IP
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printf("pi = %.5f", 4*atan(1.0));
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.SH "SEE ALSO"
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.BR putc (3),
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.BR scanf (3),
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.BR ecvt (3),
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.BR stdarg (3).
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