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@@ -81,4 +81,4 @@ basic_json .. value_t</code></pre> <h2 id=template-arguments>Template arguments<
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<span class=w> </span><span class=n>basic_json</span><span class=p>,</span><span class=w> </span><span class=c1>// value_type</span>
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<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>allocator</span><span class=o><</span><span class=n>basic_json</span><span class=o>></span><span class=w> </span><span class=c1>// allocator_type</span>
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<span class=o>></span>
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</code></pre></div> <h3 id=limits_1>Limits<a class=headerlink href=#limits_1 title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the maximum depth of nesting.</p> </blockquote> <p>In this class, the array's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the <code>max_size</code> function of a <abbr title="JavaScript Object Notation">JSON</abbr> array.</p> <h3 id=storage_2>Storage<a class=headerlink href=#storage_2 title="Permanent link">¶</a></h3> <p>Arrays are stored as pointers in a <code>basic_json</code> type. That is, for any access to array values, a pointer of type <code>array_t*</code> must be dereferenced.</p> <h2 id=strings>Strings<a class=headerlink href=#strings title="Permanent link">¶</a></h2> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> strings as follows:</p> <blockquote> <p>A string is a sequence of zero or more Unicode characters.</p> </blockquote> <p>Unicode values are split by the <abbr title="JavaScript Object Notation">JSON</abbr> class into byte-sized characters during deserialization.</p> <h3 id=default-type_2>Default type<a class=headerlink href=#default-type_2 title="Permanent link">¶</a></h3> <p>With the default values for <em>StringType</em> (<code>std::string</code>), the default value for <code>string_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>.</p> <h3 id=encoding>Encoding<a class=headerlink href=#encoding title="Permanent link">¶</a></h3> <p>Strings are stored in <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoding. Therefore, functions like <code>std::string::size()</code> or <code>std::string::length()</code> return the number of <strong>bytes</strong> in the string rather than the number of characters or glyphs.</p> <h3 id=string-comparison>String comparison<a class=headerlink href=#string-comparison title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> states:</p> <blockquote> <p>Software implementations are typically required to test names of object members for equality. Implementations that transform the textual representation into sequences of Unicode code units and then perform the comparison numerically, code unit by code unit are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations that compare strings with escaped characters unconverted may incorrectly find that <code>"a\\b"</code> and <code>"a\u005Cb"</code> are not equal.</p> </blockquote> <p>This implementation is interoperable as it does compare strings code unit by code unit.</p> <h3 id=storage_3>Storage<a class=headerlink href=#storage_3 title="Permanent link">¶</a></h3> <p>String values are stored as pointers in a <code>basic_json</code> type. That is, for any access to string values, a pointer of type <code>string_t*</code> must be dereferenced.</p> <h2 id=booleans>Booleans<a class=headerlink href=#booleans title="Permanent link">¶</a></h2> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code>true</code> and <code>false</code>.</p> <h3 id=default-type_3>Default type<a class=headerlink href=#default-type_3 title="Permanent link">¶</a></h3> <p>With the default values for <em>BooleanType</em> (<code class=highlight><span class=kt>bool</span></code>), the default value for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage_4>Storage<a class=headerlink href=#storage_4 title="Permanent link">¶</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=numbers>Numbers<a class=headerlink href=#numbers title="Permanent link">¶</a></h2> <p>See the <a href=number_handling/ >number handling</a> article for a detailed discussion on how numbers are handled by this library.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be reprLine truncated
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</code></pre></div> <h3 id=limits_1>Limits<a class=headerlink href=#limits_1 title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> specifies:</p> <blockquote> <p>An implementation may set limits on the maximum depth of nesting.</p> </blockquote> <p>In this class, the array's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the <code>max_size</code> function of a <abbr title="JavaScript Object Notation">JSON</abbr> array.</p> <h3 id=storage_2>Storage<a class=headerlink href=#storage_2 title="Permanent link">¶</a></h3> <p>Arrays are stored as pointers in a <code>basic_json</code> type. That is, for any access to array values, a pointer of type <code>array_t*</code> must be dereferenced.</p> <h2 id=strings>Strings<a class=headerlink href=#strings title="Permanent link">¶</a></h2> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> strings as follows:</p> <blockquote> <p>A string is a sequence of zero or more Unicode characters.</p> </blockquote> <p>Unicode values are split by the <abbr title="JavaScript Object Notation">JSON</abbr> class into byte-sized characters during deserialization.</p> <h3 id=default-type_2>Default type<a class=headerlink href=#default-type_2 title="Permanent link">¶</a></h3> <p>With the default values for <em>StringType</em> (<code>std::string</code>), the default value for <code>string_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>.</p> <h3 id=encoding>Encoding<a class=headerlink href=#encoding title="Permanent link">¶</a></h3> <p>Strings are stored in <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoding. Therefore, functions like <code>std::string::size()</code> or <code>std::string::length()</code> return the number of <strong>bytes</strong> in the string rather than the number of characters or glyphs.</p> <h3 id=string-comparison>String comparison<a class=headerlink href=#string-comparison title="Permanent link">¶</a></h3> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> states:</p> <blockquote> <p>Software implementations are typically required to test names of object members for equality. Implementations that transform the textual representation into sequences of Unicode code units and then perform the comparison numerically, code unit by code unit are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations that compare strings with escaped characters unconverted may incorrectly find that <code>"a\\b"</code> and <code>"a\u005Cb"</code> are not equal.</p> </blockquote> <p>This implementation is interoperable as it does compare strings code unit by code unit.</p> <h3 id=storage_3>Storage<a class=headerlink href=#storage_3 title="Permanent link">¶</a></h3> <p>String values are stored as pointers in a <code>basic_json</code> type. That is, for any access to string values, a pointer of type <code>string_t*</code> must be dereferenced.</p> <h2 id=booleans>Booleans<a class=headerlink href=#booleans title="Permanent link">¶</a></h2> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code>true</code> and <code>false</code>.</p> <h3 id=default-type_3>Default type<a class=headerlink href=#default-type_3 title="Permanent link">¶</a></h3> <p>With the default values for <em>BooleanType</em> (<code class=highlight><span class=kt>bool</span></code>), the default value for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage_4>Storage<a class=headerlink href=#storage_4 title="Permanent link">¶</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=numbers>Numbers<a class=headerlink href=#numbers title="Permanent link">¶</a></h2> <p>See the <a href=number_handling/ >number handling</a> article for a detailed discussion on how numbers are handled by this library.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes numbers as follows:</p> <blockquote> <p>The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be reprLine truncated
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@@ -54,4 +54,4 @@ val=nan
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<span class=p>}</span>
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</code></pre></div> <p>Note this approach also has the advantage that it can react on non-numerical <abbr title="JavaScript Object Notation">JSON</abbr> value types such as strings.</p> <p>(Example taken from <a href="https://github.com/nlohmann/json/issues/777#issuecomment-459968458">#777</a>.)</p> </div> <h3 id=determine-number-types>Determine number types<a class=headerlink href=#determine-number-types title="Permanent link">¶</a></h3> <p>As the example in <a href=#number-conversion>Number conversion</a> shows, there are different functions to determine the type of the stored number:</p> <ul> <li><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a> returns <code class=highlight><span class=nb>true</span></code> for any number type</li> <li><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a> returns <code class=highlight><span class=nb>true</span></code> for signed and unsigned integers</li> <li><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a> returns <code class=highlight><span class=nb>true</span></code> for unsigned integers only</li> <li><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a> returns <code class=highlight><span class=nb>true</span></code> for floating-point numbers</li> <li><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a> returns <code class=highlight><span class=s>"number"</span></code> for any number type</li> <li><a href=../../../api/basic_json/type/ ><code>type()</code></a> returns a different enumerator of <a href=../../../api/basic_json/value_t/ ><code>value_t</code></a> for all number types</li> </ul> <table> <thead> <tr> <th>function</th> <th>unsigned integer</th> <th>signed integer</th> <th>floating-point</th> <th>string</th> </tr> </thead> <tbody> <tr> <td><a href=../../../api/basic_json/is_number/ ><code>is_number()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_integer/ ><code>is_number_integer()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_unsigned/ ><code>is_number_unsigned()</code></a></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/is_number_float/ ><code>is_number_float()</code></a></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> <td><code class=highlight><span class=nb>true</span></code></td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type_name/ ><code>type_name()</code></a></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"number"</span></code></td> <td><code class=highlight><span class=s>"string"</span></code></td> </tr> <tr> <td><a href=../../../api/basic_json/type/ ><code>type()</code></a></td> <td><code>number_unsigned</code></td> <td><code>number_integer</code></td> <td><code>number_float</code></td> <td><code>string</code></td> </tr> </tbody> </table> <h3 id=template-number-types>Template number types<a class=headerlink href=#template-number-types title="Permanent link">¶</a></h3> <p>The number types can be changed with template parameters.</p> <table> <thead> <tr> <th>position</th> <th>number type</th> <th>default type</th> <th>possible values</th> </tr> </thead> <tbody> <tr> <td>5</td> <td>signed integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>int16_t</span></code>, etc.</td> </tr> <tr> <td>6</td> <td>unsigned integers</td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span></code></td> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint32_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</spanLine truncated
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<span class=hll><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>int64_t</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>uint64_t</span><span class=p>,</span><span class=w> </span><span class=kt>long</span><span class=w> </span><span class=kt>double</span><span class=o>></span><span class=p>;</span>
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</span></code></pre></div> <p>Note values should then be parsed with <code>json_ld::parse</code> rather than <code>json::parse</code> as the latter would parse floating-point values to <code class=highlight><span class=kt>double</span></code> before then converting them to <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="September 25, 2026 18:34:58 UTC">September 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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|
||||
</span></code></pre></div> <p>Note values should then be parsed with <code>json_ld::parse</code> rather than <code>json::parse</code> as the latter would parse floating-point values to <code class=highlight><span class=kt>double</span></code> before then converting them to <code class=highlight><span class=kt>long</span><span class=w> </span><span class=kt>double</span></code>.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="September 25, 2026 19:56:39 UTC">September 25, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright © 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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|
||||
@@ -562,7 +562,11 @@ binary32 or binary64 field and have no encoding for `#!cpp long double`.
|
||||
## `AllocatorType`
|
||||
|
||||
`AllocatorType` is instantiated with **one** argument, for each of `object_t`, `array_t`, `string_t`, `binary_t`,
|
||||
`basic_json`, and `#!cpp std::pair<const StringType, basic_json>`.
|
||||
`basic_json`, `#!cpp std::pair<const StringType, basic_json>`, and `#!cpp std::pair<StringType, basic_json>`.
|
||||
|
||||
`AllocatorType` is not the only allocator a `basic_json` uses. It allocates the JSON values themselves, but most
|
||||
temporary storage is allocated with `#!cpp std::allocator`. This includes the parser's stacks and the stacks that
|
||||
process deeply nested values without recursion.
|
||||
|
||||
### Always required
|
||||
|
||||
|
||||
@@ -540,7 +540,7 @@
|
||||
<span class=w> </span><span class=nt>"pi"</span><span class=p>:</span><span class=w> </span><span class=mf>3.141</span>
|
||||
<span class=p>}</span>
|
||||
<span class=kc>true</span>
|
||||
</code></pre></div> </details> <h2 id=booleantype><code>BooleanType</code><a class=headerlink href=#booleantype title="Permanent link">¶</a></h2> <p><code>boolean_t</code> is stored <strong>directly</strong> inside <code>basic_json</code>, as a member of an anonymous union.</p> <h3 id=always-required_3>Always required<a class=headerlink href=#always-required_3 title="Permanent link">¶</a></h3> <ul> <li>A literal type that is trivially default-constructible, trivially copyable, and trivially destructible; otherwise the union's special member functions are deleted.</li> <li><strong>Implicitly</strong> convertible from <code class=highlight><span class=kt>bool</span></code> -- an <code class=highlight><span class=k>explicit</span></code> constructor is not enough, because the <code>to_json</code> overload for a custom <code>BooleanType</code> is constrained on <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_convertible</span></code> -- and contextually convertible to <code class=highlight><span class=kt>bool</span></code> (here an <code class=highlight><span class=k>explicit</span><span class=w> </span><span class=k>operator</span><span class=w> </span><span class=kt>bool</span></code> is fine).</li> <li>Comparison operators <code>==</code>, <code>!=</code>, <code><</code>, <code><=</code>, <code>></code>, <code>>=</code> (or <code><=></code>).</li> <li>Convertible from and to <code class=highlight><span class=kt>bool</span></code> through the serializer, because <a href=../../../api/basic_json/get/ ><code>get<bool>()</code></a> is used internally.</li> </ul> <p>There is little reason to use anything other than <code class=highlight><span class=kt>bool</span></code> here.</p> <h3 id=compatible-types_1>Compatible types<a class=headerlink href=#compatible-types_1 title="Permanent link">¶</a></h3> <p><code class=highlight><span class=kt>bool</span></code> is the only usable choice. Another trivially copyable type that is implicitly convertible to and from <code class=highlight><span class=kt>bool</span></code> -- <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span></code>, say -- does compile, and <abbr title="JavaScript Object Notation">JSON</abbr> booleans still round-trip, but the type then serves as both <code>boolean_t</code> and an ordinary integer: <code>basic_json</code> can no longer be constructed or assigned from a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span></code> at all (the boolean and unsigned-integer <code>to_json</code> overloads become ambiguous), and <a href=../../../api/basic_json/get/ ><code>get<std::uint8_t>()</code></a> on a number throws <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> instead of returning the value.</p> <h2 id=numberintegertype-and-numberunsignedtype><code>NumberIntegerType</code> and <code>NumberUnsignedType</code><a class=headerlink href=#numberintegertype-and-numberunsignedtype title="Permanent link">¶</a></h2> <p>Both types are stored <strong>directly</strong> inside <code>basic_json</code>'s union.</p> <h3 id=always-required_4>Always required<a class=headerlink href=#always-required_4 title="Permanent link">¶</a></h3> <ul> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code> must be satisfied: <code>NumberIntegerType</code> must be a <strong>signed</strong> integer type, <code>NumberUnsignedType</code> an <strong>unsigned</strong> integer type. Class types are not supported -- among others, the constructors taking integer values are constrained on <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code>.</li> <li>Trivially default-constructible, trivially copyable, and trivially destructible (union member).</li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span></code> must be specialized for both types.</li> <li><code>NumberUnsignedType</code> must be able to represent the absolute value of every <code>NumberIntegerType</code> value; serialization of negative numbers converts the value to <code>NumberUnsignedType</code>. A <code class=highlight><span class=k>static_assert</span></code> requires it to be at least as wide as <code>NumberIntegerType</code>, which is what that amounts to for the standard integer types.</li> <li>Both types must fit into the internal 64-character number buffer used by <a href=../../../api/basic_json/dump/ ><code>dump</code></a>, which is the case for all standard integer types.</li> <li><a href=../../../api/basic_json/std_hash/ ><code>std::hash<basic_json></code></a> additionally requires <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>hash</span></code> specializations.</li> </ul> <h3 id=notes_1>Line truncated
|
||||
</code></pre></div> </details> <h2 id=booleantype><code>BooleanType</code><a class=headerlink href=#booleantype title="Permanent link">¶</a></h2> <p><code>boolean_t</code> is stored <strong>directly</strong> inside <code>basic_json</code>, as a member of an anonymous union.</p> <h3 id=always-required_3>Always required<a class=headerlink href=#always-required_3 title="Permanent link">¶</a></h3> <ul> <li>A literal type that is trivially default-constructible, trivially copyable, and trivially destructible; otherwise the union's special member functions are deleted.</li> <li><strong>Implicitly</strong> convertible from <code class=highlight><span class=kt>bool</span></code> -- an <code class=highlight><span class=k>explicit</span></code> constructor is not enough, because the <code>to_json</code> overload for a custom <code>BooleanType</code> is constrained on <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_convertible</span></code> -- and contextually convertible to <code class=highlight><span class=kt>bool</span></code> (here an <code class=highlight><span class=k>explicit</span><span class=w> </span><span class=k>operator</span><span class=w> </span><span class=kt>bool</span></code> is fine).</li> <li>Comparison operators <code>==</code>, <code>!=</code>, <code><</code>, <code><=</code>, <code>></code>, <code>>=</code> (or <code><=></code>).</li> <li>Convertible from and to <code class=highlight><span class=kt>bool</span></code> through the serializer, because <a href=../../../api/basic_json/get/ ><code>get<bool>()</code></a> is used internally.</li> </ul> <p>There is little reason to use anything other than <code class=highlight><span class=kt>bool</span></code> here.</p> <h3 id=compatible-types_1>Compatible types<a class=headerlink href=#compatible-types_1 title="Permanent link">¶</a></h3> <p><code class=highlight><span class=kt>bool</span></code> is the only usable choice. Another trivially copyable type that is implicitly convertible to and from <code class=highlight><span class=kt>bool</span></code> -- <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span></code>, say -- does compile, and <abbr title="JavaScript Object Notation">JSON</abbr> booleans still round-trip, but the type then serves as both <code>boolean_t</code> and an ordinary integer: <code>basic_json</code> can no longer be constructed or assigned from a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span></code> at all (the boolean and unsigned-integer <code>to_json</code> overloads become ambiguous), and <a href=../../../api/basic_json/get/ ><code>get<std::uint8_t>()</code></a> on a number throws <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> instead of returning the value.</p> <h2 id=numberintegertype-and-numberunsignedtype><code>NumberIntegerType</code> and <code>NumberUnsignedType</code><a class=headerlink href=#numberintegertype-and-numberunsignedtype title="Permanent link">¶</a></h2> <p>Both types are stored <strong>directly</strong> inside <code>basic_json</code>'s union.</p> <h3 id=always-required_4>Always required<a class=headerlink href=#always-required_4 title="Permanent link">¶</a></h3> <ul> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code> must be satisfied: <code>NumberIntegerType</code> must be a <strong>signed</strong> integer type, <code>NumberUnsignedType</code> an <strong>unsigned</strong> integer type. Class types are not supported -- among others, the constructors taking integer values are constrained on <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>is_integral</span></code>.</li> <li>Trivially default-constructible, trivially copyable, and trivially destructible (union member).</li> <li><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>numeric_limits</span></code> must be specialized for both types.</li> <li><code>NumberUnsignedType</code> must be able to represent the absolute value of every <code>NumberIntegerType</code> value; serialization of negative numbers converts the value to <code>NumberUnsignedType</code>. A <code class=highlight><span class=k>static_assert</span></code> requires it to be at least as wide as <code>NumberIntegerType</code>, which is what that amounts to for the standard integer types.</li> <li>Both types must fit into the internal 64-character number buffer used by <a href=../../../api/basic_json/dump/ ><code>dump</code></a>, which is the case for all standard integer types.</li> <li><a href=../../../api/basic_json/std_hash/ ><code>std::hash<basic_json></code></a> additionally requires <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>hash</span></code> specializations.</li> </ul> <h3 id=notes_1>Line truncated
|
||||
</code></pre></div> <h3 id=always-required_8>Always required<a class=headerlink href=#always-required_8 title="Permanent link">¶</a></h3> <ul> <li>A non-<code>final</code> class type -- <a href=../../../api/byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> derives from it publicly.</li> <li>A member type <code>value_type</code> that is <strong>exactly one byte</strong> wide (e.g., <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span></code>, <code class=highlight><span class=kt>char</span></code>, or <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>byte</span></code>). Readers and writers reinterpret the container's storage as raw bytes, so a wider <code>value_type</code> is rejected with a <code class=highlight><span class=k>static_assert</span></code>.</li> <li>Contiguous storage: the binary readers <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>memcpy</span></code> into <code class=highlight><span class=o>&</span><span class=n>binary</span><span class=p>[</span><span class=n>n</span><span class=p>]</span></code>, the writers <code>reinterpret_cast</code> <code>data()</code>. <code class=highlight><span class=n>data</span><span class=p>()</span><span class=w> </span><span class=o>+</span><span class=w> </span><span class=n>n</span></code> would do for the readers too, but they share one helper with <a href=#stringtype><code>StringType</code></a>, whose non-<code class=highlight><span class=k>const</span></code> <code>data()</code> is C++17 and later only.</li> <li>Default-constructible, copy-constructible, and move-constructible.</li> <li>Member functions <code>size()</code>, <code>empty()</code>, <code>data()</code>, <code>resize()</code>, <code>operator[]</code>, <code>back()</code>, <code>begin()</code>, <code>end()</code>, <code>cbegin()</code>, and <code>cend()</code> with random-access iterators, and <code>insert(pos, first, last)</code>, which the <abbr title="Concise Binary Object Representation">CBOR</abbr> reader uses to join the chunks of an indefinite-length byte string. <code>push_back()</code> is <strong>not</strong> required.</li> <li>Comparison operators: <code>==</code> is used by <a href=../../../api/byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a>, the relational operators by <a href=../../../api/basic_json/operator_le/ ><code>basic_json</code>'s comparison operators</a>.</li> </ul> <h3 id=required-for-individual-functions_1>Required for individual functions<a class=headerlink href=#required-for-individual-functions_1 title="Permanent link">¶</a></h3> <ul> <li><code>clear()</code>, for <a href=../../../api/basic_json/clear/ ><code>basic_json::clear()</code></a>.</li> </ul> <p><code>max_size()</code>, <code>at()</code>, <code>reserve()</code>, <code>erase()</code>, <code>pop_back()</code>, and <code>emplace_back()</code> are <strong>not</strong> used at all.</p> <p>See <a href=../../../api/basic_json/binary_t/ ><code>binary_t</code></a> for how a non-default <code>BinaryType</code> changes the meaning of assigning such a container to a <code>basic_json</code> value.</p> <div class="admonition tip"> <p class=admonition-title>Reference implementation</p> <p><code>docs/mkdocs/docs/examples/custom_binary_type.hpp</code> wraps a private <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code> and satisfies every requirement above -- a good starting point for a custom <code>BinaryType</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#pragma once</span>
|
||||
|
||||
<span class=cp>#include</span><span class=w> </span><span class=cpf><cstdint></span>
|
||||
@@ -676,4 +676,4 @@
|
||||
<span class=p>}</span>
|
||||
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>1</span><span class=p>,</span><span class=mi>2</span><span class=p>,</span><span class=mi>3</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=kc>null</span><span class=p>}</span>
|
||||
<span class=kc>true</span>
|
||||
</code></pre></div> </details> <h3 id=compatible-containers_2>Compatible containers<a class=headerlink href=#compatible-containers_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Notes</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code> (default)</td> <td></td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=kt>char</span><span class=o>></span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>></span></code></td> <td><code>dump()</code> writes the bytes as 0..255 whichever is used</td> </tr> <tr> <td><code>boost::container::vector<std::uint8_t></code>, <code>boost::container::small_vector<std::uint8_t, N></code></td> <td></td> </tr> <tr> <td><code>absl::InlinedVector<std::uint8_t, N></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because the value type is complete</td> </tr> <tr> <td><code>eastl::vector<std::uint8_t></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because <code>max_size()</code> is not needed</td> </tr> <tr> <td><code>folly::fbvector<std::uint8_t></code></td> <td>requires C++20, see the note above</td> </tr> </tbody> </table> <h3 id=containers-that-cannot-be-used_2>Containers that cannot be used<a class=headerlink href=#containers-that-cannot-be-used_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Reason</th> </tr> </thead> <tbody> <tr> <td><code>QByteArray</code></td> <td>no <code>empty()</code> (it spells that <code>isEmpty()</code>); its <code>insert</code> takes an index rather than an iterator; and it converts to <code>string_t</code>, which makes <code>to_json</code> ambiguous between a string and a binary value</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code></td> <td><code>binary_t::container_type</code> and <code>string_t</code> would be the same type, so the two <a href=../../../api/basic_json/swap/ ><code>swap</code></a> overloads collide and <code>basic_json</code> cannot be instantiated at all</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code></td> <td>storage is not contiguous, so there is no <code>data()</code></td> </tr> <tr> <td>containers whose <code>value_type</code> is wider than one byte</td> <td>see above -- accepted by the compiler, wrong at runtime</td> </tr> </tbody> </table> <h2 id=custombaseclass><code>CustomBaseClass</code><a class=headerlink href=#custombaseclass title="Permanent link">¶</a></h2> <p><code>CustomBaseClass</code> is an extension point: unless it is <code class=highlight><span class=kt>void</span></code> (the default, which selects the empty <code>nlohmann::json_default_base</code>), <code>basic_json</code> publicly derives from it.</p> <h3 id=always-required_9>Always required<a class=headerlink href=#always-required_9 title="Permanent link">¶</a></h3> <ul> <li>A non-<code>final</code>, default-constructible class type.</li> <li><code>basic_json</code> is copy-/move-constructible and copy-/move-assignable only if <code>CustomBaseClass</code> is.</li> </ul> <h3 id=notes_2>Notes<a class=headerlink href=#notes_2 title="Permanent link">¶</a></h3> <p><code>basic_json</code> is documented to be a <a href="https://en.cppreference.com/w/cpp/named_req/StandardLayoutType">StandardLayoutType</a>. Because <code>basic_json</code> has non-static data members of its own, a <code>CustomBaseClass</code> with non-static data members forfeits this guarantee.</p> <p>Note the namespace of <code>CustomBaseClass</code> becomes an associated namespace of <code>basic_json</code> for the purpose of argument-dependent lookup.</p> <p>See <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a> for an example.</p> <h3 id=compatible-types_6>Compatible types<a class=headerlink href=#compatible-types_6 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Type</th> <th>Support</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=kt>void</span></code> (default)</td> <td>an empty base class is used; no effect on <code>basic_json</code></td> </tr> <tr> <td>any default-constructible, non-<code>final</code> class</td> <td>full; see <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a></td> </tr>Line truncated
|
||||
</code></pre></div> </details> <h3 id=compatible-containers_2>Compatible containers<a class=headerlink href=#compatible-containers_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Notes</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code> (default)</td> <td></td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=kt>char</span><span class=o>></span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>></span></code></td> <td><code>dump()</code> writes the bytes as 0..255 whichever is used</td> </tr> <tr> <td><code>boost::container::vector<std::uint8_t></code>, <code>boost::container::small_vector<std::uint8_t, N></code></td> <td></td> </tr> <tr> <td><code>absl::InlinedVector<std::uint8_t, N></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because the value type is complete</td> </tr> <tr> <td><code>eastl::vector<std::uint8_t></code></td> <td>usable here, unlike as an <code>ArrayType</code>, because <code>max_size()</code> is not needed</td> </tr> <tr> <td><code>folly::fbvector<std::uint8_t></code></td> <td>requires C++20, see the note above</td> </tr> </tbody> </table> <h3 id=containers-that-cannot-be-used_2>Containers that cannot be used<a class=headerlink href=#containers-that-cannot-be-used_2 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Container</th> <th>Reason</th> </tr> </thead> <tbody> <tr> <td><code>QByteArray</code></td> <td>no <code>empty()</code> (it spells that <code>isEmpty()</code>); its <code>insert</code> takes an index rather than an iterator; and it converts to <code>string_t</code>, which makes <code>to_json</code> ambiguous between a string and a binary value</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code></td> <td><code>binary_t::container_type</code> and <code>string_t</code> would be the same type, so the two <a href=../../../api/basic_json/swap/ ><code>swap</code></a> overloads collide and <code>basic_json</code> cannot be instantiated at all</td> </tr> <tr> <td><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span><span class=o><</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>></span></code></td> <td>storage is not contiguous, so there is no <code>data()</code></td> </tr> <tr> <td>containers whose <code>value_type</code> is wider than one byte</td> <td>see above -- accepted by the compiler, wrong at runtime</td> </tr> </tbody> </table> <h2 id=custombaseclass><code>CustomBaseClass</code><a class=headerlink href=#custombaseclass title="Permanent link">¶</a></h2> <p><code>CustomBaseClass</code> is an extension point: unless it is <code class=highlight><span class=kt>void</span></code> (the default, which selects the empty <code>nlohmann::json_default_base</code>), <code>basic_json</code> publicly derives from it.</p> <h3 id=always-required_9>Always required<a class=headerlink href=#always-required_9 title="Permanent link">¶</a></h3> <ul> <li>A non-<code>final</code>, default-constructible class type.</li> <li><code>basic_json</code> is copy-/move-constructible and copy-/move-assignable only if <code>CustomBaseClass</code> is.</li> </ul> <h3 id=notes_2>Notes<a class=headerlink href=#notes_2 title="Permanent link">¶</a></h3> <p><code>basic_json</code> is documented to be a <a href="https://en.cppreference.com/w/cpp/named_req/StandardLayoutType">StandardLayoutType</a>. Because <code>basic_json</code> has non-static data members of its own, a <code>CustomBaseClass</code> with non-static data members forfeits this guarantee.</p> <p>Note the namespace of <code>CustomBaseClass</code> becomes an associated namespace of <code>basic_json</code> for the purpose of argument-dependent lookup.</p> <p>See <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a> for an example.</p> <h3 id=compatible-types_6>Compatible types<a class=headerlink href=#compatible-types_6 title="Permanent link">¶</a></h3> <table> <thead> <tr> <th>Type</th> <th>Support</th> </tr> </thead> <tbody> <tr> <td><code class=highlight><span class=kt>void</span></code> (default)</td> <td>an empty base class is used; no effect on <code>basic_json</code></td> </tr> <tr> <td>any default-constructible, non-<code>final</code> class</td> <td>full; see <a href=../../../api/basic_json/json_base_class_t/ ><code>json_base_class_t</code></a></td> </tr>Line truncated
|
||||
@@ -928,7 +928,9 @@ If `std::numeric_limits<NumberFloatType>` describes an IEEE 754 binary32 or bina
|
||||
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||||
## `AllocatorType`
|
||||
|
||||
`AllocatorType` is instantiated with **one** argument, for each of `object_t`, `array_t`, `string_t`, `binary_t`, `basic_json`, and `std::pair<const StringType, basic_json>`.
|
||||
`AllocatorType` is instantiated with **one** argument, for each of `object_t`, `array_t`, `string_t`, `binary_t`, `basic_json`, `std::pair<const StringType, basic_json>`, and `std::pair<StringType, basic_json>`.
|
||||
|
||||
`AllocatorType` is not the only allocator a `basic_json` uses. It allocates the JSON values themselves, but most temporary storage is allocated with `std::allocator`. This includes the parser's stacks and the stacks that process deeply nested values without recursion.
|
||||
|
||||
### Always required
|
||||
|
||||
|
||||
Reference in new issue
Block a user