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<!DOCTYPE html>
<html>
<head><title>dec64_string</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style>
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.dec64, h1, h2 {
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</head>
<body>
<a href="http://www.DEC64.com/"><img src="dec64.png" alt="DEC64" width="398" height="103" border="0"></a>
<h1>dec64_string.c</h1>
<p>One of the most difficult problems in floating-point systems is the
conversion of numbers to text. This conversion is important because humans
generally cannot use binary representations, and there are not simple, exact
transformations between familiar decimal representations and binary
floating-point. It can be difficult and expensive to find representations
that are accurate, minimal, and unsurprising. </p><br>
<table>
<tr>
<th scope="col"> </th>
<th align="center" scope="col"><code>0.1 + 0.2</code></th>
<th align="center" scope="col"><code>10 / 3</code></th>
<th align="center" scope="col"><code>10.1 - 9.93</code></th>
</tr>
<tr>
<th>IEEE754</th>
<td><pre>0.30000000000000004</pre></td>
<td><pre>3.3333333333333335</pre></td>
<td><pre>0.16999999999999993</pre></td>
</tr>
<tr>
<th><span class=dec64>DEC64</span></th>
<td align="left"><pre>0.3</pre></td>
<td><pre>3.3333333333333333</pre></td>
<td align="left"><pre>0.17</pre></td>
</tr>
</table>
<p>One of <span class=dec64>DEC64</span>'s advantages is that it easily and
accurately converts to decimal representations, requiring only slightly
more effort than the conversion of integers.</p>
<p><a href="https://github.com/douglascrockford/DEC64/blob/master/dec64_string.c">
dec64_string.c</a> contains functions for converting
<span class=dec64>DEC64</span> numbers to strings and back again.
<a href="https://github.com/douglascrockford/DEC64/blob/master/dec64_text.h">
dec64_string.h</a> includes C function prototypes for these functions:</p>
<pre>dec64 <a href="#dec64_from_string"><b>dec64_from_string</b></a>(
dec64_string_state state,
dec64_string_char string[]
)</pre>
<pre>dec64_string_state <a href="#dec64_string_begin"><b>dec64_string_begin</b></a>()</pre>
<pre>dec64_string_char <a href="#dec64_string_decimal_point"><b>dec64_string_decimal_point</b></a>(
dec64_string_state state,
dec64_string_char decimal_point
)</pre>
<pre>void <a href="#dec64_string_end"><b>dec64_string_end</b></a>(
dec64_string_state state
)</pre>
<pre>void <a href="#dec64_string_engineering"><b>dec64_string_engineering</b></a>(
dec64_string_state state
)</pre>
<pre>int <a href="#dec64_string_places"><b>dec64_string_places</b></a>(
dec64_string_state state,
dec64_string_char places
)</pre>
<pre>void <a href="#dec64_string_scientific"><b>dec64_string_scientific</b></a>(
dec64_string_state state
)</pre>
<pre>int <a href="#dec64_string_separation"><b>dec64_string_separation</b></a>(
dec64_string_state state,
int separation
)</pre>
<pre>dec64_string_char <a href="#dec64_string_separator"><b>dec64_string_separator</b></a>(
dec64_string_state state,
dec64_string_char separator
)</pre>
<pre>void <a href="#dec64_string_standard"><b>dec64_string_standard</b></a>(
dec64_string_state state
)</pre>
<pre>int <a href="#dec64_to_string"><b>dec64_to_string</b></a>(
dec64_string_state state,
dec64 number,
dec64_string_char string[]
)</pre>
<p>Two types are provided:</p>
<ul>
<li><code><b>dec64_string_char</b></code></li>
<li><code> <b>dec64_string_state</b></code></li>
</ul>
<h2 id="state">String State</h2>
<p>These functions are reentrant and thread safe. This is accomplished by use of
a state object that is created by
<code><a href="#dec64_string_begin">dec64_string_begin</a></code> and
destroyed by <code><a href="#dec64_string_end">dec64_string_end</a></code>.
All of these functions require a state object as the first argument. The
state argument allows for customizing the conversions. Do not attempt to
modify the string state object directly. Use the provided functions instead.
State objects are reusable.</p>
<p>The state object contains the output mode: standard, scientific, or engineering.</p>
<h2 id="creation">Creation</h2>
<pre>dec64_string_state <a id="dec64_string_begin"><b>dec64_string_begin</b></a>()</pre>
<p><code>dec64_string_begin</code> creates a state object. The object should be
passed to all of the other functions.</p>
<h2 id="destruction">Destruction</h2>
<pre>void <a id="dec64_string_end"><b>dec64_string_end</b></a>(
dec64_string_state state
)</pre>
<p><code>dec64_string_end</code> destroys and deallocates a state object.</p>
<h2 id="configuration">Configuration</h2>
<p>The following functions configure or customize a state object.</p>
<pre>void <a id="dec64_string_standard"><b>dec64_string_standard</b></a>(
dec64_string_state state
)</pre>
<p>Put <code><a href="#dec64_to_string">dec64_to_string</a></code> into standard
mode. Separators can be inserted between some digits if requested. If the
number might be too long, then scientific mode might be used instead.</p>
<p>Standard mode is the default.</p>
<pre>void <a id="dec64_string_scientific"><b>dec64_string_scientific</b></a>(
dec64_string_state state
)</pre>
<p>Put <code><a href="#dec64_to_string">dec64_to_string</a></code> into scientific mode, in which the coefficient is
displayed with one digit before the decimal point, and an exponent prefixed
with '<code>e</code>' is appended if necessary.</p>
<pre>void <a id="dec64_string_engineering"><b>dec64_string_engineering</b></a>(
dec64_string_state state
)</pre>
<p>Put <a href="#dec64_to_string"><code>dec64_to_string</code></a> into
engineering mode, which is like scientific mode except that the exponent is
constrained to be a multiple of 3. There can be up to three digits before
the decimal point.</p>
<pre>dec64_string_char <a id="dec64_string_decimal_point"><b>dec64_string_decimal_point</b></a>(
dec64_string_state state,
dec64_string_char decimal_point
)</pre>
<p>Specify the decimal point character. This is used by both
<code><a href="#dec64_to_string">dec64_to_string</a></code> and
<code><a href="#dec64_from_string">dec64_from_string</a></code>.
The default is '<code>.</code>'. If it is '<code>\0</code>', then the
decimal point will be suppressed.</p>
<p> It returns the previous value.</p>
<pre>int <a id="dec64_string_places"><b>dec64_string_places</b></a>(
dec64_string_state state,
dec64_string_char places
)</pre>
<p>Specify the minimum number of decimal places output by
<a href="#dec64_to_string"><code>dec64_to_string</code></a> in standard
mode. This is commonly used to format money values. The default is
<code>0</code>.</p>
<p> It returns the previous value.</p>
<pre>dec64_string_char <a id="dec64_string_separator"><b>dec64_string_separator</b></a>(
dec64_string_state state,
dec64_string_char separator
)</pre>
<p>Specify the separation character, which is used by
<code><a href="#dec64_to_string">dec64_to_string</a></code> in standard
mode to improve the readability of digits before the decimal point. Typical
values include</p>
<blockquote>
'<code>,</code>' '<code> </code>' '<code>_</code>' '<code>.</code>' '<code>\0</code>' </p>
</blockquote>
<p>If it is '<code>\0</code>', then separation will be
suppressed. The default is '<code>\0</code>'.</p>
<p><code><a href="#dec64_from_string">dec64_from_string</a></code> will ignore
this character.</p>
<p>It returns the previous value.</p>
<pre>int <a id="dec64_string_separation"><b>dec64_string_separation</b></a>(
dec64_string_state state,
int separation
)</pre>
<p>Specify the number of digits output between separators by
<code><a href="#dec64_to_string">dec64_to_string</a></code> in standard
mode. If separation is <code>1</code> or less, then separation is
suppressed. The default is <code>3</code>.</p>
<p> It returns the previous value.</p>
<h2 id="action">Action</h2>
<pre>dec64 <a id="dec64_from_string"><b>dec64_from_string</b></a>(
dec64_string_state state,
dec64_string_char string[]
)</pre>
<p><code>dec64_from_string</code> converts a zero-delimited string into a <code>dec64</code>. Separator
characters will be ignored. If conversion is not possible for any reason,
the result will be <code>DEC64_NULL</code>.</p>
<pre>int <a id="dec64_to_string"><b>dec64_to_string</b></a>(
dec64_string_state state,
dec64 number,
dec64_string_char string[]
)</pre>
<p><code>dec64_to_string</code> converts a <code>dec64</code> number into a
string. The caller provides the memory into which to deposit the string. The
provided string must have sufficient capacity to hold 32 characters. It
returns the number of characters actually deposited in the string (not
including the trailing '<code>\0</code>'). If the number is <var>nan</var>,
then it returns <code>0</code> indicating an empty string. If
<code>NULL</code> is passed in as the string, then no characters will be
deposited, but a character count will be returned.</p>
<p>In standard mode, the number will be formatted conventionally unless it
would require more than 17 digits, which would be due to excessive
trailing zeros or zeros immediately after the decimal point. In that
case scientific notation will be used instead.</p>
<h2 id="examples">Examples</h2>
<table>
<tr>
<td><pre>dec64_string_state state = dec64_string_begin();
dec64_to_string(state, dec64_new(10, -128), string);</pre></td>
<td><pre>"1e-127"</pre></td>
</tr>
<tr>
<td><pre>dec64_to_string(state, dec64_new(1024, 0), string);</pre></td>
<td><pre>"1024"</pre></td>
</tr>
<tr>
<td><pre>dec64_separator(state, ',');
dec64_to_string(state, dec64_new(1024, 0), string);</pre></td>
<td><pre>"1,024"</pre></td>
</tr>
<tr>
<td><pre>dec64_separator(state, ' ');
dec64_to_string(state, dec64_new(1024, 0), string);</pre></td>
<td><pre>"1 024"</pre></td>
</tr>
<tr>
<td><pre>dec64_places(state, 4);
dec64_to_string(state, dec64_new(1024, 0), string);</pre></td>
<td><pre>"1 024.0000"</pre></td>
</tr>
<tr>
<td><pre>dec64_scientific(state);
dec64_to_string(state, dec64_new(1024, 0), string);</pre></td>
<td><pre>"1.024e3"</pre></td>
</tr>
<tr>
<td><pre>dec64_from_string(state, "1 024.0000")</pre></td>
<td><pre>1024</pre></td>
</tr>
<tr>
<td><pre>dec64_from_string(state, "1,024.0000")</pre></td>
<td><pre>DEC64_NULL</pre></td>
</tr>
<tr>
<td><pre>dec64_separator(state, ',');
dec64_from_string(state, "1,024.0000")</pre></td>
<td><pre>1024</pre></td>
</tr>
<tr>
<td><pre>dec64_string_end(state);</pre></td>
<td><pre> </pre></td>
</tr>
</table>
</body>
</html>