231 lines
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231 lines
11 KiB
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<HTML><HEAD><TITLE>Tcl Built-In Commands - format manual page</TITLE></HEAD><BODY>
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<DL>
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<DD><A HREF="format.htm#M2" NAME="L403">NAME</A>
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<DL><DD>format - Format a string in the style of sprintf</DL>
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<DD><A HREF="format.htm#M3" NAME="L404">SYNOPSIS</A>
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<DL>
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<DD><B>format </B><I>formatString </I>?<I>arg arg ...</I>?
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</DL>
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<DD><A HREF="format.htm#M4" NAME="L405">INTRODUCTION</A>
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<DD><A HREF="format.htm#M5" NAME="L406">DETAILS ON FORMATTING</A>
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<DL>
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<DD><A HREF="format.htm#M6" NAME="L407"><B>-</B></A>
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<DD><A HREF="format.htm#M7" NAME="L408"><B>+</B></A>
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<DD><A HREF="format.htm#M8" NAME="L409"><I>space</I></A>
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<DD><A HREF="format.htm#M9" NAME="L410"><B>0</B></A>
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<DD><A HREF="format.htm#M10" NAME="L411"><B>#</B></A>
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</DL>
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<DL>
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<DD><A HREF="format.htm#M11" NAME="L412"><B>d</B></A>
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<DD><A HREF="format.htm#M12" NAME="L413"><B>u</B></A>
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<DD><A HREF="format.htm#M13" NAME="L414"><B>i</B></A>
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<DD><A HREF="format.htm#M14" NAME="L415"><B>o</B></A>
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<DD><A HREF="format.htm#M15" NAME="L416"><B>x</B> or <B>X</B></A>
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<DD><A HREF="format.htm#M16" NAME="L417"><B>c</B></A>
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<DD><A HREF="format.htm#M17" NAME="L418"><B>s</B></A>
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<DD><A HREF="format.htm#M18" NAME="L419"><B>f</B></A>
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<DD><A HREF="format.htm#M19" NAME="L420"><B>e</B> or <B>e</B></A>
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<DD><A HREF="format.htm#M20" NAME="L421"><B>g</B> or <B>G</B></A>
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<DD><A HREF="format.htm#M21" NAME="L422"><B>%</B></A>
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</DL>
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<DD><A HREF="format.htm#M22" NAME="L423">DIFFERENCES FROM ANSI SPRINTF</A>
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<DL>
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</DL>
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<DD><A HREF="format.htm#M23" NAME="L424">SEE ALSO</A>
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<DD><A HREF="format.htm#M24" NAME="L425">KEYWORDS</A>
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</DL><HR>
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<H3><A NAME="M2">NAME</A></H3>
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format - Format a string in the style of sprintf
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<H3><A NAME="M3">SYNOPSIS</A></H3>
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<B>format </B><I>formatString </I>?<I>arg arg ...</I>?<BR>
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<H3><A NAME="M4">INTRODUCTION</A></H3>
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This command generates a formatted string in the same way as the
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ANSI C <B>sprintf</B> procedure (it uses <B>sprintf</B> in its
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implementation).
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<I>FormatString</I> indicates how to format the result, using
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<B>%</B> conversion specifiers as in <B>sprintf</B>, and the additional
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arguments, if any, provide values to be substituted into the result.
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The return value from <B>format</B> is the formatted string.
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<H3><A NAME="M5">DETAILS ON FORMATTING</A></H3>
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The command operates by scanning <I>formatString</I> from left to right.
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Each character from the format string is appended to the result
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string unless it is a percent sign.
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If the character is a <B>%</B> then it is not copied to the result string.
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Instead, the characters following the <B>%</B> character are treated as
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a conversion specifier.
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The conversion specifier controls the conversion of the next successive
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<I>arg</I> to a particular format and the result is appended to
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the result string in place of the conversion specifier.
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If there are multiple conversion specifiers in the format string,
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then each one controls the conversion of one additional <I>arg</I>.
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The <B>format</B> command must be given enough <I>arg</I>s to meet the needs
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of all of the conversion specifiers in <I>formatString</I>.
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<P>
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Each conversion specifier may contain up to six different parts:
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an XPG3 position specifier,
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a set of flags, a minimum field width, a precision, a length modifier,
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and a conversion character.
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Any of these fields may be omitted except for the conversion character.
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The fields that are present must appear in the order given above.
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The paragraphs below discuss each of these fields in turn.
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<P>
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If the <B>%</B> is followed by a decimal number and a <B>$</B>, as in
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``<B>%2$d</B>'', then the value to convert is not taken from the
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next sequential argument.
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Instead, it is taken from the argument indicated by the number,
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where 1 corresponds to the first <I>arg</I>.
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If the conversion specifier requires multiple arguments because
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of <B>*</B> characters in the specifier then
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successive arguments are used, starting with the argument
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given by the number.
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This follows the XPG3 conventions for positional specifiers.
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If there are any positional specifiers in <I>formatString</I>
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then all of the specifiers must be positional.
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<P>
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The second portion of a conversion specifier may contain any of the
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following flag characters, in any order:
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<P>
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<DL>
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<P><DT><A NAME="M6"><B>-</B></A><DD>
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Specifies that the converted argument should be left-justified
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in its field (numbers are normally right-justified with leading
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spaces if needed).
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<P><DT><A NAME="M7"><B>+</B></A><DD>
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Specifies that a number should always be printed with a sign,
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even if positive.
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<P><DT><A NAME="M8"><I>space</I></A><DD>
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Specifies that a space should be added to the beginning of the
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number if the first character isn't a sign.
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<P><DT><A NAME="M9"><B>0</B></A><DD>
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Specifies that the number should be padded on the left with
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zeroes instead of spaces.
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<P><DT><A NAME="M10"><B>#</B></A><DD>
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Requests an alternate output form. For <B>o</B> and <B>O</B>
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conversions it guarantees that the first digit is always <B>0</B>.
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For <B>x</B> or <B>X</B> conversions, <B>0x</B> or <B>0X</B> (respectively)
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will be added to the beginning of the result unless it is zero.
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For all floating-point conversions (<B>e</B>, <B>E</B>, <B>f</B>,
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<B>g</B>, and <B>G</B>) it guarantees that the result always
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has a decimal point.
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For <B>g</B> and <B>G</B> conversions it specifies that
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trailing zeroes should not be removed.
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<P></DL>
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<P>
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The third portion of a conversion specifier is a number giving a
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minimum field width for this conversion.
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It is typically used to make columns line up in tabular printouts.
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If the converted argument contains fewer characters than the
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minimum field width then it will be padded so that it is as wide
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as the minimum field width.
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Padding normally occurs by adding extra spaces on the left of the
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converted argument, but the <B>0</B> and <B>-</B> flags
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may be used to specify padding with zeroes on the left or with
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spaces on the right, respectively.
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If the minimum field width is specified as <B>*</B> rather than
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a number, then the next argument to the <B>format</B> command
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determines the minimum field width; it must be a numeric string.
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<P>
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The fourth portion of a conversion specifier is a precision,
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which consists of a period followed by a number.
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The number is used in different ways for different conversions.
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For <B>e</B>, <B>E</B>, and <B>f</B> conversions it specifies the number
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of digits to appear to the right of the decimal point.
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For <B>g</B> and <B>G</B> conversions it specifies the total number
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of digits to appear, including those on both sides of the decimal
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point (however, trailing zeroes after the decimal point will still
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be omitted unless the <B>#</B> flag has been specified).
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For integer conversions, it specifies a minimum number of digits
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to print (leading zeroes will be added if necessary).
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For <B>s</B> conversions it specifies the maximum number of characters to be
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printed; if the string is longer than this then the trailing characters will be dropped.
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If the precision is specified with <B>*</B> rather than a number
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then the next argument to the <B>format</B> command determines the precision;
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it must be a numeric string.
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<P>
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The fifth part of a conversion specifier is a length modifier,
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which must be <B>h</B> or <B>l</B>.
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If it is <B>h</B> it specifies that the numeric value should be
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truncated to a 16-bit value before converting.
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This option is rarely useful.
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The <B>l</B> modifier is ignored.
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<P>
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The last thing in a conversion specifier is an alphabetic character
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that determines what kind of conversion to perform.
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The following conversion characters are currently supported:
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<P>
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<DL>
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<P><DT><A NAME="M11"><B>d</B></A><DD>
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Convert integer to signed decimal string.
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<P><DT><A NAME="M12"><B>u</B></A><DD>
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Convert integer to unsigned decimal string.
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<P><DT><A NAME="M13"><B>i</B></A><DD>
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Convert integer to signed decimal string; the integer may either be
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in decimal, in octal (with a leading <B>0</B>) or in hexadecimal
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(with a leading <B>0x</B>).
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<P><DT><A NAME="M14"><B>o</B></A><DD>
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Convert integer to unsigned octal string.
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<P><DT><A NAME="M15"><B>x</B> or <B>X</B></A><DD>
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Convert integer to unsigned hexadecimal string, using digits
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``0123456789abcdef'' for <B>x</B> and ``0123456789ABCDEF'' for <B>X</B>).
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<P><DT><A NAME="M16"><B>c</B></A><DD>
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Convert integer to the Unicode character it represents.
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<P><DT><A NAME="M17"><B>s</B></A><DD>
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No conversion; just insert string.
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<P><DT><A NAME="M18"><B>f</B></A><DD>
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Convert floating-point number to signed decimal string of
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the form <I>xx.yyy</I>, where the number of <I>y</I>'s is determined by
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the precision (default: 6).
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If the precision is 0 then no decimal point is output.
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<P><DT><A NAME="M19"><B>e</B> or <B>e</B></A><DD>
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Convert floating-point number to scientific notation in the
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form <I>x.yyy</I><B>e±</B><I>zz</I>, where the number of <I>y</I>'s is determined
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by the precision (default: 6).
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If the precision is 0 then no decimal point is output.
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If the <B>E</B> form is used then <B>E</B> is
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printed instead of <B>e</B>.
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<P><DT><A NAME="M20"><B>g</B> or <B>G</B></A><DD>
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If the exponent is less than -4 or greater than or equal to the
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precision, then convert floating-point number as for <B>%e</B> or
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<B>%E</B>.
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Otherwise convert as for <B>%f</B>.
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Trailing zeroes and a trailing decimal point are omitted.
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<P><DT><A NAME="M21"><B>%</B></A><DD>
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No conversion: just insert <B>%</B>.
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<P></DL>
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<P>
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For the numerical conversions the argument being converted must
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be an integer or floating-point string; format converts the argument
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to binary and then converts it back to a string according to
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the conversion specifier.
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<H3><A NAME="M22">DIFFERENCES FROM ANSI SPRINTF</A></H3>
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The behavior of the format command is the same as the
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ANSI C <B>sprintf</B> procedure except for the following
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differences:
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<P>
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<DL>
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<P><DT>[1]<DD>
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<B>%p</B> and <B>%n</B> specifiers are not currently supported.
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<P><DT>[2]<DD>
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For <B>%c</B> conversions the argument must be a decimal string,
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which will then be converted to the corresponding character value.
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<P><DT>[3]<DD>
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The <B>l</B> modifier is ignored; integer values are always converted
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as if there were no modifier present and real values are always
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converted as if the <B>l</B> modifier were present (i.e. type
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<B>double</B> is used for the internal representation).
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If the <B>h</B> modifier is specified then integer values are truncated
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to <B>short</B> before conversion.
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<P></DL>
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<H3><A NAME="M23">SEE ALSO</A></H3>
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<B>sprintf</B>, <B><A HREF="../TkCmd/string.htm">string</A></B>
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<H3><A NAME="M24">KEYWORDS</A></H3>
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<A href="../Keywords/C.htm#conversion specifier">conversion specifier</A>, <A href="../Keywords/F.htm#format">format</A>, <A href="../Keywords/S.htm#sprintf">sprintf</A>, <A href="../Keywords/S.htm#string">string</A>, <A href="../Keywords/S.htm#substitution">substitution</A>
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<HR><PRE>
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<A HREF="../copyright.htm">Copyright</A> © 1993 The Regents of the University of California.
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<A HREF="../copyright.htm">Copyright</A> © 1994-1996 Sun Microsystems, Inc.
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<A HREF="../copyright.htm">Copyright</A> © 1995-1997 Roger E. Critchlow Jr.</PRE>
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</BODY></HTML>
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