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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/features/binary_values/" rel="canonical"><link href=../binary_formats/ubjson/ rel=prev><link href=../comments/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Binary Values - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new 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xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> Binary Values </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio 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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <Line truncated
class binary_t ["json::binary_t"] {
+void set_subtype(std::uint64_t subtype)
@@ -46,7 +46,7 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=nt>"subtype"</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <div class="admonition warning"> <p class=admonition-title>No roundtrip for binary values</p> <p>The <abbr title="JavaScript Object Notation">JSON</abbr> parser will not parse the objects generated by binary values back to binary values. This is by design to remain standards compliant. Serializing binary values to <abbr title="JavaScript Object Notation">JSON</abbr> is only implemented for debugging purposes.</p> </div> <h3 id=bjdata><abbr title="Binary JData">BJData</abbr><a class=headerlink href=#bjdata title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bjdata/ ><abbr title="Binary JData">BJData</abbr></a> neither supports binary values nor subtypes and proposes to serialize binary values as an array of uint8 values. The library implements this translation.</p> <details class=example> <summary>Example: serialize a binary value to <abbr title="Binary JData">BJData</abbr></summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42 (will be ignored in BJData)</span>
</code></pre></div> </details> <div class="admonition warning"> <p class=admonition-title>No roundtrip for binary values</p> <p>The <abbr title="JavaScript Object Notation">JSON</abbr> parser will not parse the objects generated by binary values back to binary values. This is by design to remain standards compliant. Serializing binary values to <abbr title="JavaScript Object Notation">JSON</abbr> is only implemented for debugging purposes.</p> </div> <h3 id=bjdata><abbr title="Binary JData">BJData</abbr><a class=headerlink href=#bjdata title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bjdata/ ><abbr title="Binary JData">BJData</abbr></a> Draft 3 supports binary values as optimized arrays of <code>B</code> (byte) elements, but no subtypes. With <code>version = bjdata_version_t::draft3</code> and both <code>use_size</code> and <code>use_type</code> set, <code>to_bjdata</code> writes a binary value as <code>[$B#...</code>, and <code>from_bjdata</code> reads it back as a binary value (without subtype). In all other cases, including the default Draft 2 mode, the library follows the Draft 2 proposal and writes an array of integers (<code>U</code> in Draft 2, <code>B</code> in Draft 3), which is read back as an array.</p> <details class=example> <summary>Example: serialize a binary value to <abbr title="Binary JData">BJData</abbr></summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42 (will be ignored in BJData)</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>"binary"</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -62,14 +62,14 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
</code></pre></div> <p>The following code uses the type and size optimization for <abbr title="Binary JData">BJData</abbr>:</p> <div class=highlight><pre><span></span><code><span class=c1>// convert to BJData using the size and type optimization</span>
<span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>to_bjdata</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>);</span>
</code></pre></div> <p>The resulting vector has 22 elements; the optimization is not effective for examples with few values:</p> <div class=highlight><pre><span></span><code><span class=mh>0x7B</span><span class=w> </span><span class=c1>// '{'</span>
<span class=w> </span><span class=mh>0x23</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x01</span><span class=w> </span><span class=c1>// '#' 'i' type of the array elements: unsigned integers</span>
<span class=w> </span><span class=mh>0x23</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x01</span><span class=w> </span><span class=c1>// '#' 'i' 1 number of object members</span>
<span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x06</span><span class=w> </span><span class=c1>// i 6 (length of the key)</span>
<span class=w> </span><span class=mh>0x62</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x6E</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x72</span><span class=w> </span><span class=mh>0x79</span><span class=w> </span><span class=c1>// "binary"</span>
<span class=w> </span><span class=mh>0x5B</span><span class=w> </span><span class=c1>// '[' array</span>
<span class=w> </span><span class=mh>0x24</span><span class=w> </span><span class=mh>0x55</span><span class=w> </span><span class=c1>// '$' 'U' type of the array elements: unsigned integers</span>
<span class=w> </span><span class=mh>0x23</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x04</span><span class=w> </span><span class=c1>// '#' i 4 number of array elements</span>
<span class=w> </span><span class=mh>0xCA</span><span class=w> </span><span class=mh>0xFE</span><span class=w> </span><span class=mh>0xBA</span><span class=w> </span><span class=mh>0xBE</span><span class=w> </span><span class=c1>// content</span>
</code></pre></div> <p>Note that subtype (42) is <strong>not</strong> serialized and that <abbr title="Binary JData">BJData</abbr> has <strong>no binary type</strong>, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <p>Note that subtype (42) is <strong>not</strong> serialized and that, in Draft 2 mode, <abbr title="Binary JData">BJData</abbr> has <strong>no binary type</strong>, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"binary"</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=w> </span><span class=mi>254</span><span class=p>,</span><span class=w> </span><span class=mi>186</span><span class=p>,</span><span class=w> </span><span class=mi>190</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <h3 id=bon8><abbr title="Binary Object Notation 8">BON8</abbr><a class=headerlink href=#bon8 title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bon8/ ><abbr title="Binary Object Notation 8">BON8</abbr></a> neither supports binary values nor subtypes. The library serializes binary values as an array of integers.</p> <details class=example> <summary>Example: serialize a binary value to <abbr title="Binary Object Notation 8">BON8</abbr></summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42 (will be ignored in BON8)</span>
@@ -81,11 +81,11 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
</code></pre></div> <p><code>v</code> is a <code>std::vector&lt;std::uint8_t&gt;</code> with the following 16 elements:</p> <div class=highlight><pre><span></span><code><span class=mh>0x87</span><span class=w> </span><span class=c1>// object with 1 member</span>
<span class=w> </span><span class=mh>0x62</span><span class=w> </span><span class=mh>0x69</span><span class=w> </span><span class=mh>0x6E</span><span class=w> </span><span class=mh>0x61</span><span class=w> </span><span class=mh>0x72</span><span class=w> </span><span class=mh>0x79</span><span class=w> </span><span class=c1>// "binary"</span>
<span class=w> </span><span class=mh>0x84</span><span class=w> </span><span class=c1>// array with 4 elements</span>
<span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x22</span><span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x56</span><span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x12</span><span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x16</span><span class=w> </span><span class=c1>// content (each byte as a 2-byte integer)</span>
<span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x22</span><span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x56</span><span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x12</span><span class=w> </span><span class=mh>0xC3</span><span class=w> </span><span class=mh>0x16</span><span class=w> </span><span class=c1>// content (each byte, here all above 39, as a 2-byte integer)</span>
</code></pre></div> <p>Note that the subtype is lost, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"binary"</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=w> </span><span class=mi>254</span><span class=p>,</span><span class=w> </span><span class=mi>186</span><span class=p>,</span><span class=w> </span><span class=mi>190</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <h3 id=bson><abbr title="Binary JSON">BSON</abbr><a class=headerlink href=#bson title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bson/ ><abbr title="Binary JSON">BSON</abbr></a> supports binary values and subtypes. If a subtype is given, it is used and added as an unsigned 8-bit integer. If no subtype is given, the generic binary subtype 0x00 is used.</p> <details class=example> <summary>Example: serialize a binary value to <abbr title="Binary JSON">BSON</abbr></summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
</code></pre></div> </details> <h3 id=bson><abbr title="Binary JSON">BSON</abbr><a class=headerlink href=#bson title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/bson/ ><abbr title="Binary JSON">BSON</abbr></a> supports binary values and subtypes. If a subtype is given, it is used and added as an unsigned 8-bit integer; a subtype above 255 throws <a href=../../home/exceptions/#jsonexceptionout_of_range415><code>out_of_range.415</code></a>. If no subtype is given, the generic binary subtype 0x00 is used. The payload of the "old binary" subtype 0x02 is preceded by a second length, which the library writes and removes again when reading; it is not part of the payload.</p> <details class=example> <summary>Example: serialize a binary value to <abbr title="Binary JSON">BSON</abbr></summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>"binary"</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -116,13 +116,19 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
<span class=w> </span><span class=mh>0xD8</span><span class=w> </span><span class=mh>0x2A</span><span class=w> </span><span class=c1>// tag(42)</span>
<span class=w> </span><span class=mh>0x44</span><span class=w> </span><span class=c1>// bytes(4)</span>
<span class=w> </span><span class=mh>0xCA</span><span class=w> </span><span class=mh>0xFE</span><span class=w> </span><span class=mh>0xBA</span><span class=w> </span><span class=mh>0xBE</span><span class=w> </span><span class=c1>// content</span>
</code></pre></div> <p>Note that the subtype is serialized as tag. However, parsing tagged values yield a parse error unless <code>json::cbor_tag_handler_t::ignore</code> or <code>json::cbor_tag_handler_t::store</code> is passed to <a href=../../api/basic_json/from_cbor/ ><code>json::from_cbor</code></a> (see <a href=../../api/basic_json/cbor_tag_handler_t/ ><code>cbor_tag_handler_t</code></a>).</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
</code></pre></div> <p>Note that the subtype is serialized as tag. However, parsing tagged values yield a parse error unless <code>json::cbor_tag_handler_t::ignore</code> or <code>json::cbor_tag_handler_t::store</code> is passed to <a href=../../api/basic_json/from_cbor/ ><code>json::from_cbor</code></a> (see <a href=../../api/basic_json/cbor_tag_handler_t/ ><code>cbor_tag_handler_t</code></a>).</p> <p>With <code>ignore</code>, the subtype is dropped (<code>"subtype": null</code>); with <code>store</code>, the tag is kept (<code>"subtype": 42</code>):</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"binary"</span><span class=p>:</span><span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=nt>"bytes"</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=w> </span><span class=mi>254</span><span class=p>,</span><span class=w> </span><span class=mi>186</span><span class=p>,</span><span class=w> </span><span class=mi>190</span><span class=p>],</span>
<span class=w> </span><span class=nt>"subtype"</span><span class=p>:</span><span class=w> </span><span class=kc>null</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <h3 id=messagepack>MessagePack<a class=headerlink href=#messagepack title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/messagepack/ >MessagePack</a> supports binary values and subtypes. If a subtype is given, the ext family is used. The library will choose the smallest representation among fixext1, fixext2, fixext4, fixext8, ext8, ext16, and ext32. The subtype is then added as a signed 8-bit integer.</p> <p>If no subtype is given, the bin family (bin8, bin16, bin32) is used.</p> <details class=example> <summary>Example: serialize a binary value to MessagePack</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
</code></pre></div> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"binary"</span><span class=p>:</span><span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=nt>"bytes"</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=w> </span><span class=mi>254</span><span class=p>,</span><span class=w> </span><span class=mi>186</span><span class=p>,</span><span class=w> </span><span class=mi>190</span><span class=p>],</span>
<span class=w> </span><span class=nt>"subtype"</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <h3 id=messagepack>MessagePack<a class=headerlink href=#messagepack title="Permanent link">&para;</a></h3> <p><a href=../binary_formats/messagepack/ >MessagePack</a> supports binary values and subtypes. If a subtype is given, the ext family is used. The library will choose the smallest representation among fixext1, fixext2, fixext4, fixext8, fixext16, ext8, ext16, and ext32. The subtype is then written as the signed 8-bit ext type: subtypes 128 to 255 map to the negative (reserved) ext types, and on reading the ext type is exposed as an unsigned subtype from 0 to 255.</p> <p>If no subtype is given, the bin family (bin8, bin16, bin32) is used.</p> <details class=example> <summary>Example: serialize a binary value to MessagePack</summary> <p>Code:</p> <div class=highlight><pre><span></span><code><span class=c1>// create a binary value of subtype 42</span>
<span class=n>json</span><span class=w> </span><span class=n>j</span><span class=p>;</span>
<span class=n>j</span><span class=p>[</span><span class=s>"binary"</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>},</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
@@ -167,4 +173,4 @@ vector &lt;|-- binary_t</code></pre> <p>By default, binary values are stored as
</code></pre></div> <p>Note that subtype (42) is <strong>not</strong> serialized and that <abbr title="Universal Binary JSON">UBJSON</abbr> has <strong>no binary type</strong>, and deserializing <code>v</code> would yield the following value:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"binary"</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=w> </span><span class=mi>254</span><span class=p>,</span><span class=w> </span><span class=mi>186</span><span class=p>,</span><span class=w> </span><span class=mi>190</span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> </details> <!-- 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="October 14, 2026 15:40:55 UTC">October 14, 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 &copy; 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@@ -119,7 +119,7 @@ The JSON parser will not parse the objects generated by binary values back to bi
### BJData
[BJData](https://json.nlohmann.me/features/binary_formats/bjdata/index.md) neither supports binary values nor subtypes and proposes to serialize binary values as an array of uint8 values. The library implements this translation.
[BJData](https://json.nlohmann.me/features/binary_formats/bjdata/index.md) Draft 3 supports binary values as optimized arrays of `B` (byte) elements, but no subtypes. With `version = bjdata_version_t::draft3` and both `use_size` and `use_type` set, `to_bjdata` writes a binary value as `[$B#...`, and `from_bjdata` reads it back as a binary value (without subtype). In all other cases, including the default Draft 2 mode, the library follows the Draft 2 proposal and writes an array of integers (`U` in Draft 2, `B` in Draft 3), which is read back as an array.
Example: serialize a binary value to BJData
@@ -157,7 +157,7 @@ The resulting vector has 22 elements; the optimization is not effective for exam
```
0x7B // '{'
0x23 0x69 0x01 // '#' 'i' type of the array elements: unsigned integers
0x23 0x69 0x01 // '#' 'i' 1 number of object members
0x69 0x06 // i 6 (length of the key)
0x62 0x69 0x6E 0x61 0x72 0x79 // "binary"
0x5B // '[' array
@@ -166,7 +166,7 @@ The resulting vector has 22 elements; the optimization is not effective for exam
0xCA 0xFE 0xBA 0xBE // content
```
Note that subtype (42) is **not** serialized and that BJData has **no binary type**, and deserializing `v` would yield the following value:
Note that subtype (42) is **not** serialized and that, in Draft 2 mode, BJData has **no binary type**, and deserializing `v` would yield the following value:
```
{
@@ -197,7 +197,7 @@ auto v = json::to_bon8(j);
0x87 // object with 1 member
0x62 0x69 0x6E 0x61 0x72 0x79 // "binary"
0x84 // array with 4 elements
0xC3 0x22 0xC3 0x56 0xC3 0x12 0xC3 0x16 // content (each byte as a 2-byte integer)
0xC3 0x22 0xC3 0x56 0xC3 0x12 0xC3 0x16 // content (each byte, here all above 39, as a 2-byte integer)
```
Note that the subtype is lost, and deserializing `v` would yield the following value:
@@ -210,7 +210,7 @@ Note that the subtype is lost, and deserializing `v` would yield the following v
### BSON
[BSON](https://json.nlohmann.me/features/binary_formats/bson/index.md) supports binary values and subtypes. If a subtype is given, it is used and added as an unsigned 8-bit integer. If no subtype is given, the generic binary subtype 0x00 is used.
[BSON](https://json.nlohmann.me/features/binary_formats/bson/index.md) supports binary values and subtypes. If a subtype is given, it is used and added as an unsigned 8-bit integer; a subtype above 255 throws [`out_of_range.415`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range415). If no subtype is given, the generic binary subtype 0x00 is used. The payload of the "old binary" subtype 0x02 is preceded by a second length, which the library writes and removes again when reading; it is not part of the payload.
Example: serialize a binary value to BSON
@@ -278,6 +278,8 @@ auto v = json::to_cbor(j);
Note that the subtype is serialized as tag. However, parsing tagged values yield a parse error unless `json::cbor_tag_handler_t::ignore` or `json::cbor_tag_handler_t::store` is passed to [`json::from_cbor`](https://json.nlohmann.me/api/basic_json/from_cbor/index.md) (see [`cbor_tag_handler_t`](https://json.nlohmann.me/api/basic_json/cbor_tag_handler_t/index.md)).
With `ignore`, the subtype is dropped (`"subtype": null`); with `store`, the tag is kept (`"subtype": 42`):
```
{
"binary": {
@@ -287,9 +289,18 @@ Note that the subtype is serialized as tag. However, parsing tagged values yield
}
```
```
{
"binary": {
"bytes": [202, 254, 186, 190],
"subtype": 42
}
}
```
### MessagePack
[MessagePack](https://json.nlohmann.me/features/binary_formats/messagepack/index.md) supports binary values and subtypes. If a subtype is given, the ext family is used. The library will choose the smallest representation among fixext1, fixext2, fixext4, fixext8, ext8, ext16, and ext32. The subtype is then added as a signed 8-bit integer.
[MessagePack](https://json.nlohmann.me/features/binary_formats/messagepack/index.md) supports binary values and subtypes. If a subtype is given, the ext family is used. The library will choose the smallest representation among fixext1, fixext2, fixext4, fixext8, fixext16, ext8, ext16, and ext32. The subtype is then written as the signed 8-bit ext type: subtypes 128 to 255 map to the negative (reserved) ext types, and on reading the ext type is exposed as an unsigned subtype from 0 to 255.
If no subtype is given, the bin family (bin8, bin16, bin32) is used.