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<div class="memproto">
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<div class="memtemplate">
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template<template< typename U, typename V, typename...Args > class ObjectType = std::map, template< typename U, typename...Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = int64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator> </div>
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<td class="memname">bool <a class="el" href="classnlohmann_1_1basic__json.html">nlohmann::basic_json</a>::empty </td>
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<td>(</td>
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<td class="paramname"></td><td>)</td>
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<td> const</td>
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</tr>
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</table>
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</td>
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<td class="mlabels-right">
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<span class="mlabels"><span class="mlabel">inline</span><span class="mlabel">noexcept</span></span> </td>
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</table>
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</div><div class="memdoc">
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<p>Checks if a JSON value has no elements.</p>
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<dl class="section return"><dt>Returns</dt><dd>The return value depends on the different value types and is defined as follows: <table class="doxtable">
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<tr>
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<th>Value type </th><th>return value </th></tr>
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<tr>
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<td>null </td><td><code>true</code> </td></tr>
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<tr>
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<td>boolean </td><td><code>false</code> </td></tr>
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<tr>
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<td>string </td><td><code>false</code> </td></tr>
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<tr>
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<td>number </td><td><code>false</code> </td></tr>
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<tr>
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<td>object </td><td>result of function object_t::empty() </td></tr>
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<tr>
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<td>array </td><td>result of function array_t::empty() </td></tr>
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</table>
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</dd></dl>
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<dl class="section user"><dt>Complexity</dt><dd>Constant, as long as <a class="el" href="classnlohmann_1_1basic__json_ac82abedf356d252e0589850c3d8b35ba.html#ac82abedf356d252e0589850c3d8b35ba">array_t</a> and <a class="el" href="classnlohmann_1_1basic__json_a63691315292df8e1522b00d37ebb1ffc.html#a63691315292df8e1522b00d37ebb1ffc">object_t</a> satisfy the Container concept; that is, their <a class="el" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca" title="checks whether the container is empty ">empty()</a> functions have constant complexity.</dd></dl>
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<dl class="section user"><dt>Requirements</dt><dd>This function satisfies the Container requirements:<ul>
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<li>The complexity is constant.</li>
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<li>Has the semantics of <code><a class="el" href="classnlohmann_1_1basic__json_af4261341695729a8e657b94772f95516.html#af4261341695729a8e657b94772f95516" title="returns an iterator to the first element ">begin()</a> == <a class="el" href="classnlohmann_1_1basic__json_ad8f84e6fb9bbf9a7bc767962ad0fe3a1.html#ad8f84e6fb9bbf9a7bc767962ad0fe3a1" title="returns an iterator to one past the last element ">end()</a></code>.</li>
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</ul>
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</dd></dl>
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<dl class="section user"><dt>Example</dt><dd>The following code uses <a class="el" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a> to check if a <a class="el" href="namespacenlohmann_a2bfd99e845a2e5cd90aeaf1b1431f474.html#a2bfd99e845a2e5cd90aeaf1b1431f474">json</a> object contains any elements. <div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="preprocessor">#include <json.hpp></span></div>
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<div class="line"><a name="l00002"></a><span class="lineno"> 2</span> </div>
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<div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="keyword">using namespace </span><a class="code" href="namespacenlohmann.html">nlohmann</a>;</div>
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<div class="line"><a name="l00004"></a><span class="lineno"> 4</span> </div>
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<div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="keywordtype">int</span> main()</div>
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<div class="line"><a name="l00006"></a><span class="lineno"> 6</span> {</div>
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<div class="line"><a name="l00007"></a><span class="lineno"> 7</span>  <span class="comment">// create JSON values</span></div>
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<div class="line"><a name="l00008"></a><span class="lineno"> 8</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_null;</div>
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<div class="line"><a name="l00009"></a><span class="lineno"> 9</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_boolean = <span class="keyword">true</span>;</div>
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<div class="line"><a name="l00010"></a><span class="lineno"> 10</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_number_integer = 17;</div>
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<div class="line"><a name="l00011"></a><span class="lineno"> 11</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_number_float = 23.42;</div>
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<div class="line"><a name="l00012"></a><span class="lineno"> 12</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_object = {{<span class="stringliteral">"one"</span>, 1}, {<span class="stringliteral">"two"</span>, 2}};</div>
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<div class="line"><a name="l00013"></a><span class="lineno"> 13</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_object_empty(<a class="code" href="classnlohmann_1_1basic__json_a231b02148577b69a154b2ce2c87a5522.html#a231b02148577b69a154b2ce2c87a5522aa8cfde6331bd59eb2ac96f8911c4b666">json::value_t::object</a>);</div>
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<div class="line"><a name="l00014"></a><span class="lineno"> 14</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_array = {1, 2, 4, 8, 16};</div>
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<div class="line"><a name="l00015"></a><span class="lineno"> 15</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_array_empty(<a class="code" href="classnlohmann_1_1basic__json_a231b02148577b69a154b2ce2c87a5522.html#a231b02148577b69a154b2ce2c87a5522af1f713c9e000f5d3f280adbd124df4f5">json::value_t::array</a>);</div>
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<div class="line"><a name="l00016"></a><span class="lineno"> 16</span>  <a class="code" href="classnlohmann_1_1basic__json.html">json</a> j_string = <span class="stringliteral">"Hello, world"</span>;</div>
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<div class="line"><a name="l00017"></a><span class="lineno"> 17</span> </div>
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<div class="line"><a name="l00018"></a><span class="lineno"> 18</span>  <span class="comment">// call empty()</span></div>
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<div class="line"><a name="l00019"></a><span class="lineno"> 19</span>  std::cout << std::boolalpha;</div>
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<div class="line"><a name="l00020"></a><span class="lineno"> 20</span>  std::cout << j_null.<a class="code" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a>() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00021"></a><span class="lineno"> 21</span>  std::cout << j_boolean.<a class="code" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a>() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00022"></a><span class="lineno"> 22</span>  std::cout << j_number_integer.<a class="code" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a>() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00023"></a><span class="lineno"> 23</span>  std::cout << j_number_float.<a class="code" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a>() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00024"></a><span class="lineno"> 24</span>  std::cout << j_object.<a class="code" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a>() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00025"></a><span class="lineno"> 25</span>  std::cout << j_object_empty.empty() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00026"></a><span class="lineno"> 26</span>  std::cout << j_array.<a class="code" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a>() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00027"></a><span class="lineno"> 27</span>  std::cout << j_array_empty.empty() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00028"></a><span class="lineno"> 28</span>  std::cout << j_string.<a class="code" href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">empty</a>() << <span class="charliteral">'\n'</span>;</div>
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<div class="line"><a name="l00029"></a><span class="lineno"> 29</span> }</div>
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<div class="ttc" id="classnlohmann_1_1basic__json_html"><div class="ttname"><a href="classnlohmann_1_1basic__json.html">nlohmann::basic_json</a></div><div class="ttdoc">a class to store JSON values </div><div class="ttdef"><b>Definition:</b> json.hpp:113</div></div>
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<div class="ttc" id="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca_html_a572cdf681c75b42c2bc38a1fbe993eca"><div class="ttname"><a href="classnlohmann_1_1basic__json_a572cdf681c75b42c2bc38a1fbe993eca.html#a572cdf681c75b42c2bc38a1fbe993eca">nlohmann::basic_json::empty</a></div><div class="ttdeci">bool empty() const noexcept</div><div class="ttdoc">checks whether the container is empty </div><div class="ttdef"><b>Definition:</b> json.hpp:2265</div></div>
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<div class="ttc" id="classnlohmann_1_1basic__json_a231b02148577b69a154b2ce2c87a5522_html_a231b02148577b69a154b2ce2c87a5522aa8cfde6331bd59eb2ac96f8911c4b666"><div class="ttname"><a href="classnlohmann_1_1basic__json_a231b02148577b69a154b2ce2c87a5522.html#a231b02148577b69a154b2ce2c87a5522aa8cfde6331bd59eb2ac96f8911c4b666">nlohmann::basic_json::value_t::object</a></div><div class="ttdoc">object (unordered set of name/value pairs) </div></div>
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<div class="ttc" id="namespacenlohmann_html"><div class="ttname"><a href="namespacenlohmann.html">nlohmann</a></div><div class="ttdoc">namespace for Niels Lohmann </div><div class="ttdef"><b>Definition:</b> json.hpp:49</div></div>
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<div class="ttc" id="classnlohmann_1_1basic__json_a231b02148577b69a154b2ce2c87a5522_html_a231b02148577b69a154b2ce2c87a5522af1f713c9e000f5d3f280adbd124df4f5"><div class="ttname"><a href="classnlohmann_1_1basic__json_a231b02148577b69a154b2ce2c87a5522.html#a231b02148577b69a154b2ce2c87a5522af1f713c9e000f5d3f280adbd124df4f5">nlohmann::basic_json::value_t::array</a></div><div class="ttdoc">array (ordered collection of values) </div></div>
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</div><!-- fragment --> Output: <pre class="fragment">true
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false
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false
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false
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false
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true
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false
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true
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false
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</pre> The example code above can be translated with<pre class="fragment">g++ -std=c++11 -Isrc doc/examples/empty.cpp -o empty </pre>. </dd></dl>
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<li class="footer">Generated on Sun Jun 21 2015 21:49:32 for JSON for Modern C++ by
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<img class="footer" src="doxygen.png" alt="doxygen"/></a> 1.8.9.1 </li>
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