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<div class="section" id="rfc-conformance">
<span id="id1"></span><h1>RFC Conformance<a class="headerlink" href="#rfc-conformance" title="Permalink to this headline">¶</a></h1>
<p>JSON is specified in <span class="target" id="index-0"></span><a class="rfc reference external" href="http://tools.ietf.org/html/rfc4627.html"><strong>RFC 4627</strong></a>, <em>“The application/json Media Type
for JavaScript Object Notation (JSON)”</em>.</p>
<div class="section" id="character-encoding">
<h2>Character Encoding<a class="headerlink" href="#character-encoding" title="Permalink to this headline">¶</a></h2>
<p>Jansson only supports UTF-8 encoded JSON texts. It does not support or
auto-detect any of the other encodings mentioned in the RFC, namely
UTF-16LE, UTF-16BE, UTF-32LE or UTF-32BE. Pure ASCII is supported, as
it’s a subset of UTF-8.</p>
</div>
<div class="section" id="strings">
<h2>Strings<a class="headerlink" href="#strings" title="Permalink to this headline">¶</a></h2>
<p>JSON strings are mapped to C-style null-terminated character arrays,
and UTF-8 encoding is used internally. Strings may not contain
embedded null characters, not even escaped ones.</p>
<p>For example, trying to decode the following JSON text leads to a parse
error:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="p">[</span><span class="s">"this string contains the null character: </span><span class="se">\u0000</span><span class="s">"</span><span class="p">]</span>
</pre></div>
</div>
<p>All other Unicode codepoints U+0001 through U+10FFFF are allowed.</p>
<p>Unicode normalization or any other transformation is never performed
on any strings (string values or object keys). When checking for
equivalence of strings or object keys, the comparison is performed
byte by byte between the original UTF-8 representations of the
strings.</p>
</div>
<div class="section" id="numbers">
<h2>Numbers<a class="headerlink" href="#numbers" title="Permalink to this headline">¶</a></h2>
<div class="section" id="real-vs-integer">
<h3>Real vs. Integer<a class="headerlink" href="#real-vs-integer" title="Permalink to this headline">¶</a></h3>
<p>JSON makes no distinction between real and integer numbers; Jansson
does. Real numbers are mapped to the <tt class="docutils literal"><span class="pre">double</span></tt> type and integers to
the <tt class="docutils literal"><span class="pre">json_int_t</span></tt> type, which is a typedef of <tt class="docutils literal"><span class="pre">long</span> <span class="pre">long</span></tt> or
<tt class="docutils literal"><span class="pre">long</span></tt>, depending on whether <tt class="docutils literal"><span class="pre">long</span> <span class="pre">long</span></tt> is supported by your
compiler or not.</p>
<p>A JSON number is considered to be a real number if its lexical
representation includes one of <tt class="docutils literal"><span class="pre">e</span></tt>, <tt class="docutils literal"><span class="pre">E</span></tt>, or <tt class="docutils literal"><span class="pre">.</span></tt>; regardless if
its actual numeric value is a true integer (e.g., all of <tt class="docutils literal"><span class="pre">1E6</span></tt>,
<tt class="docutils literal"><span class="pre">3.0</span></tt>, <tt class="docutils literal"><span class="pre">400E-2</span></tt>, and <tt class="docutils literal"><span class="pre">3.14E3</span></tt> are mathematical integers, but
will be treated as real values).</p>
<p>All other JSON numbers are considered integers.</p>
<p>When encoding to JSON, real values are always represented
with a fractional part; e.g., the <tt class="docutils literal"><span class="pre">double</span></tt> value 3.0 will be
represented in JSON as <tt class="docutils literal"><span class="pre">3.0</span></tt>, not <tt class="docutils literal"><span class="pre">3</span></tt>.</p>
</div>
<div class="section" id="overflow-underflow-precision">
<h3>Overflow, Underflow & Precision<a class="headerlink" href="#overflow-underflow-precision" title="Permalink to this headline">¶</a></h3>
<p>Real numbers whose absolute values are too small to be represented in
a C <tt class="docutils literal"><span class="pre">double</span></tt> will be silently estimated with 0.0. Thus, depending on
platform, JSON numbers very close to zero such as 1E-999 may result in
0.0.</p>
<p>Real numbers whose absolute values are too large to be represented in
a C <tt class="docutils literal"><span class="pre">double</span></tt> will result in an overflow error (a JSON decoding
error). Thus, depending on platform, JSON numbers like 1E+999 or
-1E+999 may result in a parsing error.</p>
<p>Likewise, integer numbers whose absolute values are too large to be
represented in the <tt class="docutils literal"><span class="pre">json_int_t</span></tt> type (see above) will result in an
overflow error (a JSON decoding error). Thus, depending on platform,
JSON numbers like 1000000000000000 may result in parsing error.</p>
<p>Parsing JSON real numbers may result in a loss of precision. As long
as overflow does not occur (i.e. a total loss of precision), the
rounded approximate value is silently used. Thus the JSON number
1.000000000000000005 may, depending on platform, result in the
<tt class="docutils literal"><span class="pre">double</span></tt> value 1.0.</p>
</div>
<div class="section" id="signed-zeros">
<h3>Signed zeros<a class="headerlink" href="#signed-zeros" title="Permalink to this headline">¶</a></h3>
<p>JSON makes no statement about what a number means; however Javascript
(ECMAscript) does state that +0.0 and -0.0 must be treated as being
distinct values, i.e. -0.0 ≠ 0.0. Jansson relies on the
underlying floating point library in the C environment in which it is
compiled. Therefore it is platform-dependent whether 0.0 and -0.0 will
be distinct values. Most platforms that use the IEEE 754
floating-point standard will support signed zeros.</p>
<p>Note that this only applies to floating-point; neither JSON, C, or
IEEE support the concept of signed integer zeros.</p>
</div>
<div class="section" id="types">
<h3>Types<a class="headerlink" href="#types" title="Permalink to this headline">¶</a></h3>
<p>No support is provided in Jansson for any C numeric types other than
<tt class="docutils literal"><span class="pre">json_int_t</span></tt> and <tt class="docutils literal"><span class="pre">double</span></tt>. This excludes things such as unsigned
types, <tt class="docutils literal"><span class="pre">long</span> <span class="pre">double</span></tt>, etc. Obviously, shorter types like <tt class="docutils literal"><span class="pre">short</span></tt>,
<tt class="docutils literal"><span class="pre">int</span></tt>, <tt class="docutils literal"><span class="pre">long</span></tt> (if <tt class="docutils literal"><span class="pre">json_int_t</span></tt> is <tt class="docutils literal"><span class="pre">long</span> <span class="pre">long</span></tt>) and <tt class="docutils literal"><span class="pre">float</span></tt>
are implicitly handled via the ordinary C type coercion rules (subject
to overflow semantics). Also, no support or hooks are provided for any
supplemental “bignum” type add-on packages.</p>
</div>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">RFC Conformance</a><ul>
<li><a class="reference internal" href="#character-encoding">Character Encoding</a></li>
<li><a class="reference internal" href="#strings">Strings</a></li>
<li><a class="reference internal" href="#numbers">Numbers</a><ul>
<li><a class="reference internal" href="#real-vs-integer">Real vs. Integer</a></li>
<li><a class="reference internal" href="#overflow-underflow-precision">Overflow, Underflow & Precision</a></li>
<li><a class="reference internal" href="#signed-zeros">Signed zeros</a></li>
<li><a class="reference internal" href="#types">Types</a></li>
</ul>
</li>
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</li>
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