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<html><head>
<title>ANSI C 'printf' Format</title>
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<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
<hr>
<h1>ANSI C 'printf' Format</h1>
<hr>
<p><b>Nyquist/XLISP:</b> The
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr> and
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
variables define format strings for the underlying 'sprintf' <nobr>C
function</nobr>. <nobr>In C,</nobr> the same format string specification is
used for 'fprint' [writes to <nobr>a file]</nobr>, 'printf' [writes to
standard output] and 'sprintf' [writes to another string]. These three
functions are meant in the following text with 'the printf functions'.</p>
<p><b>ANSI C:</b> The printf functions write output under control of a
format string that specifies how subsequent arguments are converted for
output. If there are insufficient arguments for the format, the behavior is
undefined. If the format is exhausted while arguments remain, the excess
arguments are evaluated but are otherwise ignored. The printf functions
return when the end of the format string is encountered.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="format-string"></a>
<hr>
<h2>Format String</h2>
<hr>
<p>The format string is composed of zero or more directives, which are
ordinary characters <nobr>[except "%"]</nobr>, 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 <nobr>character "%"</nobr>:</p>
<pre class="example">
<font color="#AA0000">%</font>[<font color="#0000CC">flags</font>][<font color="#0000CC">field-with</font>][<font color="#0000CC">precision</font>][<font color="#0000CC">data-type</font>]<font color="#880000">conversion-type</font>
</pre>
<p>After the "%", the following appear in sequence:</p>
<ul>
<li><p><b>Flags</b> - Zero or more <a href="#flags">flags</a> that modify
the meaning of the conversion specification.</p></li>
<li><p><b>Field Width</b> - <nobr>An optional</nobr> decimal integer
specifying a minimum field width. <nobr>If the</nobr> converted value has
fewer characters than the field width, it will be padded with spaces on the
left to the field width. <nobr>The field</nobr> is padded on the right if
the <nobr><a href="#minus-flag"> − </a> flag</nobr> has been
given, or padded with zeros if the
<nobr><a href="#zero-flag"> 0 </a> flag</nobr> had been
given. <nobr>A negative</nobr> integer, given as '<nobr>field width</nobr>'
argument, is interpreted as a
<nobr><a href="#minus-flag"> − </a> flag</nobr> followed by
a positive <nobr>field width</nobr>.</p></li>
<li><p><b>Precision</b> - <nobr>An optional</nobr> decimal integer that
gives the minimum number of digits to appear for
<a href="#integer">integer</a> conversions, the number of digits to appear
after the
<nobr>decimal-point</nobr> character for <nobr>floating-point</nobr>
<nobr><a href="#float-e"> e </a></nobr> and
<nobr><a href="#float-f"> f </a></nobr> conversions, or the
maximum number of significant digits for the <nobr>floating-point</nobr>
<nobr><a href="#float-g"> g </a></nobr> conversion.</p>
<p>The precision takes the form of a period character followed by an
optional decimal integer:</p>
<pre class="example">
.[<font color="#0000CC">integer</font>]
</pre>
<p><nobr>If the</nobr> integer is omitted, it is treated as zero, a
negative precision argument is taken as if it were missing.</p>
<p><b>Note:</b> <nobr>In C</nobr>, the precision also specifies the
maximum number of characters to be written from a string in <nobr>'s'
conversion</nobr>, but "%s" should not be used in the XLISP
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr> or
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
variables, otherwise XLISP will crash.</p></li>
</li>
<li><p><b>Data Type</b> - <nobr>An optional</nobr> character specifying a
<nobr><a href="#data-type">data type</a></nobr> to be used for the
conversion.</p>
<p><b>XLISP:</b> Nyquist/XLISP uses <nobr>C 'long'</nobr> signed integers
and <nobr>C 'double'</nobr> floats only, so with <nobr>floating-point</nobr>
numbers no special <nobr><a href="#data-type">data type</a></nobr> needs to
be given, while <a href="#integer">integer</a> conversions should always be
prefixed by a <nobr>'l' [lowercase L]</nobr>, otherwise the printed
representation of integer numbers may be differently than the behaviour of
the Nyquist/XLISP functions.</nobr></p></li>
<li><p><b>Conversion Type</b> - <nobr>A character</nobr> that specifies the
<nobr><a href="#conversion-type">conversion type</a></nobr> to be
applied.</p></li>
</ul>
<p><b>Not with Nyquist/XLISP:</b> <nobr>In C</nobr>, a '<nobr>field
width</nobr>' or 'precision', or both, may be indicated by an asterisk *
instead of a digit string. In this case, an int argument supplies the field
width or precision. The arguments specifying field width or precision, or
both, shall appear [in that order] before the argument [if any] to be
converted.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="flags"></a>
<hr>
<h2>Flags</h2>
<hr>
<p>The flag characters and their meanings are:</p>
<p><div class="box">
<dl>
<a name="minus-flag"></a>
<dt><p><nobr>− [minus sign character]</nobr></p></dt>
<dd><p>The result of the conversion will be <nobr>left-justified</nobr>
within the field.</p></dd>
<a name="plus-flag"></a>
<dt><p><nobr>+ [plus sign character]</nobr></p></dt>
<dd><p>The result of a signed conversion will always begin with a plus or
minus sign.</p></dd>
<a name="space-flag"></a>
<dt><p><nobr><i>space</i> [space character]</nobr></p></dt>
<dd><p>If the first character of a signed conversion is not a sign, or if a
signed conversion results in no characters, a space will be prepended to the
result. <nobr>If the</nobr> 'space' and
<nobr><a href="#plus-flag"> + </a> flags</nobr> both appear, the
'space' flag will be ignored.</p></dd>
<a name="hash-flag"></a>
<dt><p><nobr># [hash character]</nobr></p></dt>
<dd><p>The result is to be converted to an 'alternate form':</p>
<p>Octal Numbers - For o conversion, it increases the precision to force the
first digit of the result to be a zero.</p>
<p>Hexadecimal Numbers - For x or X conversion, a nonzero result will have
0x or 0X prepended to it.</p>
<p>Floating-point Numbers - For e, E, f, g, and G conversions, the result
will always contain a decimal-point character, even if no digits follow it
(normally, a decimal-point character appears in the result of these
conversions only if a digit follows it). For g and G conversions, trailing
zeros will not be removed from the result. For other conversions, the
behavior is undefined.</p>
</dd>
<a name="zero-flag"></a>
<dt><p><nobr>0 [number zero character]</nobr></p></dt>
<dd><p>For integer d, i, o, u, x, X, and floating-point e, E, f, g, G
conversions, leading zeros [following any indication of sign or base] are
used to pad to the <nobr><a href="#format-string">field width</a></nobr>.
<nobr>No <a href="#space-flag">space</a></nobr> padding is performed.
<nobr>If the</nobr> '0' and
<nobr><a href="#minus-flag"> − </a> flags</nobr> both
appear, the <nobr>'0' flag</nobr> will be ignored. For integer d, i, o, u,
x, X conversions, if a <a href="#format-string">precision</a> is specified,
the <nobr>'0' flag</nobr> will be ignored. <nobr>For other</nobr>
conversions, the behavior is undefined.</p></dd>
</dl>
</div></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="data-type"></a>
<hr>
<h2>Data Type</h2>
<hr>
<p><div class="box">
<dl>
<dt><p><nobr><b>h</b> [lowercase H character]</nobr></p></dt>
<dd><p>A following d, i, o, u, x, or X conversion specifier applies to a
short int or unsigned short int argument [the argument will have been
promoted according to the integral promotions, and its value shall be
converted to short int or unsigned short int before printing].</p>
<p>A following n conversion specifier applies to a pointer to a short int
argument.</p></dd>
<dt><p><nobr><b>l</b> [lowercase L character]</nobr></p></dt>
<dd><p>A following d, i, o, u, x, or X conversion specifier applies to a
long int or unsigned long int argument.</p>
<p>A following n conversion specifier applies to a pointer to a long int
argument.</p></dd>
<dt><p><nobr><b>L</b> [uppercase L character]</nobr></p></dt>
<dd><p>A following e, E, f, g, or G conversion specifier applies to a long
double argument.</p></dd>
</dl>
</div></p>
<p>If an h, l, or L appears with any other conversion specifier, the
behavior is undefined.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="conversion-type"></a>
<hr>
<h2>Conversion Type</h2>
<hr>
<p><b>Integer</b> conversion:</p>
<p><div class="box">
<dl>
<a name="integer"></a>
<dt><p><nobr><b>d</b>, <b>i</b>, <b>o</b>, <b>u</b>, <b>x</b>,
<b>X</b></nobr></p></dt>
<dd><p>The integer argument is converted to:
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="center"><nobr>d</nobr></td>
<td><nobr> → </nobr></td>
<td><nobr>signed decimal</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="center"><nobr>i</nobr></td>
<td><nobr> → </nobr></td>
<td><nobr>signed decimal</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="center"><nobr>o</nobr></td>
<td><nobr> → </nobr></td>
<td><nobr>unsigned octal</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="center"><nobr>u</nobr></td>
<td><nobr> → </nobr></td>
<td><nobr>unsigned decimal</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="center"><nobr>x</nobr></td>
<td><nobr> → </nobr></td>
<td><nobr>unsigned hexadecimal, using 'abcdef'</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="center"><nobr>X</nobr></td>
<td><nobr> → </nobr></td>
<td><nobr>unsigned hexadecimal, using 'ABCDEF'</nobr></td>
</tr>
</tbody></table></p>
<p>The <a href="#format-string">precision</a> specifies the minimum number
of digits to appear. <nobr>If the</nobr> value being converted can be
represented in fewer digits, it will be expanded with leading zeros. The
default precision <nobr>is 1</nobr>. The result of converting a zero value
with an explicit precision of zero results in no characters.</p>
<b>XLISP:</b> Nyquist/XLISP uses <nobr>C 'long'</nobr> signed integers, so
the integer conversions should always be prefixed by a <nobr>'l' [lowercase
L]</nobr> indicating a '<nobr>long int</nobr>' <nobr>C
<a href="#data-type">data type</a></nobr>, otherwise the printed
representation of integer numbers may be differently than the behaviour of
the Nyquist/XLISP functions.</p></dd>
</dl>
</div></p>
<p><b>Floating-point</b> conversion:</p>
<p><div class="box">
<dl>
<a name="float-f"></a>
<dt><p><b>f</b></p></dt>
<dd><p>The <nobr>floating-point</nobr> argument of <nobr>C data</nobr> type
'double' is converted to decimal notation in the style:</p>
<pre class="example">
[-]<font color="#0000CC">ddd</font>.<font color="#0000CC">ddd</font>
</pre>
<p>The number of digits after the <nobr>decimal-point</nobr> character
is equal to the <a href="#format-string">precision</a> specification.
<nobr>If the</nobr> <a href="#format-string">precision</a> is missing, it is
taken <nobr>as 6</nobr>. <nobr>If the</nobr>
<a href="#format-string">precision</a> is explicitly zero, no
<nobr>decimal-point</nobr> character appears. <nobr>If a</nobr>
<nobr>decimal-point</nobr> character appears, at least one digit appears
<nobr>before it</nobr>. <nobr>The value</nobr> is rounded to the appropriate
number of digits.</p></dd>
<a name="float-e"></a>
<dt><p><b>e</b>, <b>E</b></p></dt>
<dd><p>The <nobr>floating-point</nobr> argument of <nobr>C data</nobr> type
'double' is converted in the style:</p>
<pre class="example">
[-]<font color="#0000CC">d</font>.<font color="#0000CC">ddd</font><font color="#AA0000">e</font>+-<font color="#0000CC">dd</font>
</pre>
<p>There is one digit before the <nobr>decimal-point</nobr> character
[which is nonzero if the argument is nonzero] and the number of digits after
it is equal to the <a href="#format-string">precision</a>. <nobr>If
the</nobr> <a href="#format-string">precision</a> is missing, it is taken
<nobr>as 6</nobr>. <nobr>If the</nobr>
<a href="#format-string">precision</a> is zero, no
<nobr>decimal-point</nobr> character appears. <nobr>The value</nobr> is
rounded to the appropriate number of digits. <nobr>The exponent</nobr>
always contains at least two digits. <nobr>If the</nobr> value is zero, the
exponent is zero. <nobr>The "E"</nobr> conversion specifier will
produce a number with 'E' instead of 'e' introducing the exponent.</p> </dd>
<a name="float-g"></a>
<dt><p><b>g</b>, <b>G</b></p></dt>
<dd><p>The <nobr>floating-point</nobr> argument of <nobr>C data</nobr> type
'double' is converted in style <a href="#float-f"> f </a> or
<a href="#float-e"> e </a>, or in style
<a href="#float-e"> E </a> in the case of a "G"
conversion specifier, with the <a href="#format-string">precision</a>
specifying the number of significant digits. <nobr>If an</nobr> explicit
<a href="#format-string">precision</a> is zero, it is taken <nobr>as
1</nobr>. <nobr>The style</nobr> used depends on the value converted.
<nobr>Style <a href="#float-"> e </a></nobr> will be used only if
the exponent resulting from such a conversion is less <nobr>than -4</nobr>
or greater than or equal to the <a href="#format-string">precision</a>.
Trailing zeros are removed from the fractional portion of the result.
<nobr>A decimal-point</nobr> character appears only if it is followed by
<nobr>a digit</nobr>.</p></dd>
</dl>
</div></p>
<p>If a conversion specification is invalid, the behavior is undefined.
<nobr>In no</nobr> case does a nonexistent or small
<nobr><a href="#format-string">field width</a></nobr> cause truncation of a
field. <nobr>If the</nobr> result of a conversion is wider than the
<nobr><a href="#format-string">field width</a></nobr>, the field is expanded
to contain the conversion result.</p>
<p>The minimum value for the maximum number of characters produced by
any single conversion shall be 509.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="other-conversion-types"></a>
<hr>
<h2>Other Conversion Types</h2>
<hr>
<p>This section contains a list of all other conversion types defined
<nobr>in ANSI C</nobr>.</p>
<p><b>Warning:</b> Do <b>not</b> use thse conversions with the XLISP
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr> and
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
variables, because XLISP will produce nonsense or just simply will crash.
<nobr>The XLISP</nobr> behaviour described below was tested with
<nobr>Nyquist 3.03</nobr> in <nobr>December 2010</nobr>, compiled with
<nobr>GCC 4.3.2</nobr> and <nobr>glibc 2.7</nobr> on <nobr>Debian 5
[Lenny]</nobr>. <nobr>The behaviour</nobr> may be different with different
Nyquist or XLISP versions, different <nobr>C compilers</nobr> and/or
libraries, or different operating systems.</p>
<p><div class="box">
<dl>
<dt><p><b>c</b></p></dt>
<dd><p><b>ANSI C:</b> The integer argument is converted to an
'<nobr>unsigned char</nobr>', and the resulting character is written.</p>
<p><b>XLISP:</b> If the
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr> or
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
is set <nobr>to "%c"</nobr>, then the lowest <nobr>8 bit</nobr>
of the internal binary representation of the respective numbers will be
printed as an <a href="ascii-table.htm">ASCII</a> character.</p></dd>
<dt><p><b>s</b></p></dt>
<dd><p><b>ANSI C:</b> The argument shall be a pointer to an array of
character type. Characters from the array are written up to [but not
including] a terminating null character. <nobr>If the</nobr>
<a href="#format-string">precision</a> is specified, no more than that many
characters are written. <nobr>If the</nobr>
<a href="#format-string">precision</a> is not specified or is greater than
the size of the array, the array shall contain a null character.</p>
<b>XLISP:</b> If the
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr> or
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
is set to "%s" and XLISP tries to print a respective number,
XLISP crashes.</dd>
<dt><p><b>p</b></p></dt>
<dd><p><b>ANSI C:</b> The argument shall be a pointer to 'void'. The value
of the pointer is converted to a sequence of printable characters, in an
<nobr>implementation-defined</nobr> manner.</p>
<p><b>XLISP:</b> If the
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr>
is set <nobr>to "%p"</nobr>, then floating-point numbers are
printed <nobr>as "(nil)"</nobr>. <nobr>If the</nobr>
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
is set <nobr>to "%p"</nobr>, the integer numbers are printed as
hexadecimal numbers, prefixed <nobr>with "0x"</nobr>.</p></dd>
<dt><p><b>n</b></p></dt>
<dd><p><b>ANSI C:</b> The argument shall be a pointer to an integer into
which is written the number of characters written to the output stream so
far by this call to the <nobr>C 'fprintf'</nobr> function.<nobr> No
argument</nobr> is converted.</p>
<b>XLISP:</b> If the
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr> or
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
is set to "%n" and XLISP tries to print a respective number,
XLISP crashes.</dd>
<dt><p><b>%</b></p></dt>
<dd><p><nobr><b>ANSI C:</b> A "%"</nobr> is written. <nobr>No
argument</nobr> is converted. <nobr>The complete</nobr> conversion
specification <nobr>shall be "%%"</nobr>.</p>
<b>XLISP:</b> If the
<nobr><a href="../reference/global-float-format.htm">*float-format*</a></nobr>
is set to "%g%%" or the
<nobr><a href="../reference/global-integer-format.htm">*integer-format*</a></nobr>
is set to "%ld%%" then all respective numbers will be printed
with a <nobr>trailing "%"</nobr>.</dd>
</dl>
</div></p>
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