xbd_chap05.html

IEEE 1003.1-2003, Single Unix Specification v3

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<p>Each conversion specification is introduced by the percent-sign character ( <tt>'%'</tt> ). After the character <tt>'%'</tt> ,
the following shall appear in sequence:</p>

<dl compact>
<dt><i>flags</i></dt>

<dd>Zero or more <i>flags</i>, in any order, that modify the meaning of the conversion specification.</dd>

<dt><i>field&nbsp;width</i></dt>

<dd>An optional string of decimal digits to specify a minimum field width. For an output field, if the converted value has fewer
bytes than the field width, it shall be padded on the left (or right, if the left-adjustment flag ( <tt>'-'</tt> ), described
below, has been given) to the field width.</dd>

<dt><i>precision</i></dt>

<dd>Gives the minimum number of digits to appear for the <tt>d</tt> , <tt>o</tt> , <tt>i</tt> , <tt>u</tt> , <tt>x</tt> , or
<tt>X</tt> conversion specifiers (the field is padded with leading zeros), the number of digits to appear after the radix character
for the <tt>e</tt> and <tt>f</tt> conversion specifiers, the maximum number of significant digits for the <tt>g</tt> conversion
specifier; or the maximum number of bytes to be written from a string in the <tt>s</tt> conversion specifier. The precision shall
take the form of a period ( <tt>'.'</tt> ) followed by a decimal digit string; a null digit string is treated as zero.</dd>

<dt><i>conversion specifier characters</i></dt>

<dd><br>
A conversion specifier character (see below) that indicates the type of conversion to be applied.</dd>
</dl>

<p>The <i>flag</i> characters and their meanings are:</p>

<dl compact>
<dt><tt>-</tt></dt>

<dd>The result of the conversion shall be left-justified within the field.</dd>

<dt><tt>+</tt></dt>

<dd>The result of a signed conversion shall always begin with a sign ( <tt>'+'</tt> or <tt>'-'</tt> ).</dd>

<dt>&lt;space&gt;</dt>

<dd>If the first character of a signed conversion is not a sign, a &lt;space&gt; shall be prefixed to the result. This means that
if the &lt;space&gt; and <tt>'+'</tt> flags both appear, the &lt;space&gt; flag shall be ignored.</dd>

<dt><tt>#</tt></dt>

<dd>The value shall be converted to an alternative form. For <tt>c</tt> , <tt>d</tt> , <tt>i</tt> , <tt>u</tt> , and <tt>s</tt>
conversion specifiers, the behavior is undefined. For the <tt>o</tt> conversion specifier, it shall increase the precision to force
the first digit of the result to be a zero. For <tt>x</tt> or <tt>X</tt> conversion specifiers, a non-zero result has 0x or 0X
prefixed to it, respectively. For <tt>e</tt> , <tt>E</tt> , <tt>f</tt> , <tt>g</tt> , and <tt>G</tt> conversion specifiers, the
result shall always contain a radix character, even if no digits follow the radix character. For <tt>g</tt> and <tt>G</tt>
conversion specifiers, trailing zeros shall not be removed from the result as they usually are.</dd>

<dt><tt>0</tt></dt>

<dd>For <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , <tt>X</tt> , <tt>e</tt> , <tt>E</tt> , <tt>f</tt> ,
<tt>g</tt> , and <tt>G</tt> conversion specifiers, leading zeros (following any indication of sign or base) shall be used to pad to
the field width; no space padding is performed. If the <tt>'0'</tt> and <tt>'-'</tt> flags both appear, the <tt>'0'</tt> flag shall
be ignored. For <tt>d</tt> , <tt>i</tt> , <tt>o</tt> , <tt>u</tt> , <tt>x</tt> , and <tt>X</tt> conversion specifiers, if a
precision is specified, the <tt>'0'</tt> flag shall be ignored. For other conversion specifiers, the behavior is undefined.</dd>
</dl>

<p>Each conversion specifier character shall result in fetching zero or more arguments. The results are undefined if there are
insufficient arguments for the format. If the format is exhausted while arguments remain, the excess arguments shall be
ignored.</p>

<p>The conversion specifiers and their meanings are:</p>

<dl compact>
<dt><tt>d</tt>,<tt>i</tt>,<tt>o</tt>,<tt>u</tt>,<tt>x</tt>,<tt>X</tt></dt>

<dd>The integer argument shall be written as signed decimal ( <tt>d</tt> or <tt>i</tt> ), unsigned octal ( <tt>o</tt> ), unsigned
decimal ( <tt>u</tt> ), or unsigned hexadecimal notation ( <tt>x</tt> and <tt>X</tt> ). The <tt>d</tt> and <tt>i</tt> specifiers
shall convert to signed decimal in the style <tt>"[-]</tt><i>dddd</i><tt>"</tt>. The <tt>x</tt> conversion specifier shall use the
numbers and letters <tt>"0123456789abcdef"</tt> and the <tt>X</tt> conversion specifier shall use the numbers and letters
<tt>"0123456789ABCDEF"</tt> . The <i>precision</i> component of the argument shall specify the minimum number of digits to appear.
If the value being converted can be represented in fewer digits than the specified minimum, it shall be expanded with leading
zeros. The default precision shall be 1. The result of converting a zero value with a precision of 0 shall be no characters. If
both the field width and precision are omitted, the implementation may precede, follow, or precede and follow numeric arguments of
types <tt>d</tt> , <tt>i</tt> , and <tt>u</tt> with &lt;blank&gt;s; arguments of type <tt>o</tt> (octal) may be preceded with
leading zeros.</dd>

<dt><tt>f</tt></dt>

<dd>The floating-point number argument shall be written in decimal notation in the style <b>[</b>-<b>]</b><i>ddd.ddd</i>, where the
number of digits after the radix character (shown here as a decimal point) shall be equal to the <i>precision</i> specification.
The <i>LC_NUMERIC</i> locale category shall determine the radix character to use in this format. If the <i>precision</i> is omitted
from the argument, six digits shall be written after the radix character; if the <i>precision</i> is explicitly 0, no radix
character shall appear.</dd>

<dt><tt>e</tt>,<tt>E</tt></dt>

<dd>The floating-point number argument shall be written in the style <b>[</b>-<b>]</b><i>d.ddd</i>e<i>&plusmn;dd</i> (the symbol
<tt>'&plusmn;'</tt> indicates either a plus or minus sign), where there is one digit before the radix character (shown here as a
decimal point) and the number of digits after it is equal to the precision. The <i>LC_NUMERIC</i> locale category shall determine
the radix character to use in this format. When the precision is missing, six digits shall be written after the radix character; if
the precision is 0, no radix character shall appear. The <tt>E</tt> conversion specifier shall produce a number with <tt>E</tt>
instead of <tt>e</tt> introducing the exponent. The exponent shall always contain at least two digits. However, if the value to be
written requires an exponent greater than two digits, additional exponent digits shall be written as necessary.</dd>

<dt><tt>g</tt>,<tt>G</tt></dt>

<dd>The floating-point number argument shall be written in style <tt>f</tt> or <tt>e</tt> (or in style <tt>F</tt> or <tt>E</tt> in
the case of a <tt>G</tt> conversion specifier), with the precision specifying the number of significant digits. The style used
depends on the value converted: style <tt>e</tt> (or <tt>E</tt> ) shall be used only if the exponent resulting from the conversion
is less than -4 or greater than or equal to the precision. Trailing zeros are removed from the result. A radix character shall
appear only if it is followed by a digit.</dd>

<dt><tt>c</tt></dt>

<dd>The integer argument shall be converted to an <b>unsigned char</b> and the resulting byte shall be written.</dd>

<dt><tt>s</tt></dt>

<dd>The argument shall be taken to be a string and bytes from the string shall be written until the end of the string or the number
of bytes indicated by the <i>precision</i> specification of the argument is reached. If the precision is omitted from the argument,
it shall be taken to be infinite, so all bytes up to the end of the string shall be written.</dd>

<dt><tt>%</tt></dt>

<dd>Write a <tt>'%'</tt> character; no argument is converted.</dd>
</dl>

<p>In no case does a nonexistent or insufficient field width cause truncation of a field; if the result of a conversion is wider
than the field width, the field is simply expanded to contain the conversion result. The term &quot;field width&quot; should not be
confused with the term &quot;precision&quot; used in the description of <tt>%s</tt> .</p>

<hr>
<div class="box"><em>The following sections are informative.</em></div>

<h5><a name="tag_05_00_00_01"></a>Examples</h5>

<p>To represent the output of a program that prints a date and time in the form Sunday, July 3, 10:02, where <i>weekday</i> and
<i>month</i> are strings:</p>

<blockquote>
<pre>
<tt>"%s,<img src="../images/delta.gif" border="0">%s<img src="../images/delta.gif" border="0">%d,<img src="../images/delta.gif"
border=
"0">%d:%.2d\n" &lt;</tt><i>weekday</i><tt>&gt;, &lt;</tt><i>month</i><tt>&gt;, &lt;</tt><i>day</i><tt>&gt;, &lt;</tt><i>hour</i><tt>&gt;, &lt;</tt><i>min</i><tt>&gt;
</tt>
</pre>
</blockquote>

<p>To show <tt>'<img src="../images/pi.gif" border="0">'</tt> written to 5 decimal places:</p>

<blockquote>
<pre>
<tt>"pi<img src="../images/delta.gif" border="0">=<img src="../images/delta.gif" border=
"0">%.5f\n",&lt;</tt><i>value of</i> <tt><img src="../images/pi.gif" border="0">&gt;
</tt>
</pre>
</blockquote>

<p>To show an input file format consisting of five colon-separated fields:</p>

<blockquote>
<pre>
<tt>"%s:%s:%s:%s:%s\n", &lt;</tt><i>arg1</i><tt>&gt;, &lt;</tt><i>arg2</i><tt>&gt;, &lt;</tt><i>arg3</i><tt>&gt;, &lt;</tt><i>arg4</i><tt>&gt;, &lt;</tt><i>arg5</i><tt>&gt;
</tt>
</pre>
</blockquote>

<div class="box"><em>End of informative text.</em></div>

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