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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_formats/ubjson/" rel="canonical"><link href=../messagepack/ rel=prev><link href=../../binary_values/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>UBJSON - 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 URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#ubjson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg 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> UBJSON </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 name=__palette 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23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 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> </laLine truncated
<!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_formats/ubjson/" rel="canonical"><link href=../messagepack/ rel=prev><link href=../../binary_values/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>UBJSON - 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 URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#ubjson class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg 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> UBJSON </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 name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 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> </laLine truncated
<span class=w> </span><span class=nt>"id"</span><span class=p>:</span><span class=w> </span><span class=mi>300</span><span class=p>,</span>
<span class=w> </span><span class=nt>"name"</span><span class=p>:</span><span class=w> </span><span class=s2>"json"</span><span class=p>,</span>
<span class=w> </span><span class=nt>"pi"</span><span class=p>:</span><span class=w> </span><span class=mf>3.14</span><span class=p>,</span>
<span class=w> </span><span class=nt>"tags"</span><span class=p>:</span><span class=w> </span><span class=p>[</span>
<span class=w> </span><span class=s2>"a"</span><span class=p>,</span>
<span class=w> </span><span class=s2>"b"</span>
<span class=w> </span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> <p><code>to_ubjson</code> encodes it to 51 bytes (shown in hexadecimal; the encoding contains no whitespace). The colors mark the role of each byte: <span class="bl bl-t">type/marker</span> <span class="bl bl-l">length/count/size</span> <span class="bl bl-d">data</span>.</p> <div class=byte-layout markdown=0><table> <thead><tr><th>JSON</th><th>Bytes</th><th>Meaning</th></tr></thead><tbody> <tr><td><code>{</code></td><td><span class="bl bl-t">7B</span></td><td>object start (<code>{</code>)</td></tr> <tr><td><code>&quot;id&quot;: 300,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">69 64</span> <span class="bl bl-t">49</span> <span class="bl bl-d">01 2C</span></td><td>key: length 2 as int8 (<code>i</code>), then UTF-8 bytes; value: int16 (<code>I</code>), big-endian</td></tr> <tr><td><code>&quot;name&quot;: &quot;json&quot;,</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">6E 61 6D 65</span> <span class="bl bl-t">53</span> <span class="bl bl-l">69 04</span> <span class="bl bl-d">6A 73 6F 6E</span></td><td>key: length 4; value: string (<code>S</code>), length 4 as int8, UTF-8 bytes</td></tr> <tr><td><code>&quot;pi&quot;: 3.14,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">70 69</span> <span class="bl bl-t">44</span> <span class="bl bl-d">40 09 1E B8 51 EB 85 1F</span></td><td>key: length 2; value: float64 (<code>D</code>), big-endian</td></tr> <tr><td><code>&quot;tags&quot;: [</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">74 61 67 73</span> <span class="bl bl-t">5B</span></td><td>key: length 4; value: array start (<code>[</code>)</td></tr> <tr><td><code>&quot;a&quot;,</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">61</span></td><td>string, length 1</td></tr> <tr><td><code>&quot;b&quot;</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">62</span></td><td>string, length 1</td></tr> <tr><td><code>]</code></td><td><span class="bl bl-t">5D</span></td><td>array end (<code>]</code>)</td></tr> <tr><td><code>}</code></td><td><span class="bl bl-t">7D</span></td><td>object end (<code>}</code>)</td></tr> </tbody></table></div> <h2 id=serialization>Serialization<a class=headerlink href=#serialization title="Permanent link">&para;</a></h2> <p>The library uses the following mapping from <abbr title="JavaScript Object Notation">JSON</abbr> values types to <abbr title="Universal Binary JSON">UBJSON</abbr> types according to the <abbr title="Universal Binary JSON">UBJSON</abbr> specification:</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>value/range</th> <th><abbr title="Universal Binary JSON">UBJSON</abbr> type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code>null</code></td> <td>null</td> <td><code>Z</code></td> </tr> <tr> <td>boolean</td> <td><code>true</code></td> <td>true</td> <td><code>T</code></td> </tr> <tr> <td>boolean</td> <td><code>false</code></td> <td>false</td> <td><code>F</code></td> </tr> <tr> <td>number_integer</td> <td>-9223372036854775808..-2147483649</td> <td>int64</td> <td><code>L</code></td> </tr> <tr> <td>number_integer</td> <td>-2147483648..-32769</td> <td>int32</td> <td><code>l</code></td> </tr> <tr> <td>number_integer</td> <td>-32768..-129</td> <td>int16</td> <td><code>I</code></td> </tr> <tr> <td>number_integer</td> <td>-128..127</td> <td>int8</td> <td><code>i</code></td> </tr> <tr> <td>number_integer</td> <td>128..255</td> <td>uint8</td> <td><code>U</code></td> </tr> <tr> <td>number_integer</td> <td>256..32767</td> <td>int16</td> <td><code>I</code></td> </tr> <tr> <td>number_integer</td> <td>32768..2147483647</td> <td>int32</td> <td><code>l</code></td> </tr> <tr> <td>number_integer</td> <td>2147483648..9223372036854775807</td> <td>int64</td> <td><code>L</code></td> </tr> <tr> <td>number_unsigned</td> <td>0..127</td> <td>int8</td> <td><code>i</code></td> </tr> <tr> <td>number_unsigned</td> <td>128..255</td> <td>uint8</td> <td><code>U</code></td> </tr> <tr> <td>number_unsigned</td> <td>256..32767</td> <td>int16</td> <td><code>I</code></td> </tr> <tr> <td>number_unsigned</td> <td>32768..2147483647</td> <td>int32</td> <td><code>l</code></td> </tr> <tr> <td>number_unsigned</td> <td>2147483648..9223372036854775807</td> <td>int64</td> <td><code>L</code></td> </tr> <tr> <td>number_unsigned</td> <td>9223372036854775808..18446744073709551615</td> <td>high-precision</td> <td><code>H</code></td> </tr> <tr> <td>number_float</td> <td><em>any value</em></td> <td>float64 (float32 if <code>number_float_t</code> is <code>float</code>)</td> <td><code>D</code> (<code>d</code>)</td> </tr> <tr> <td>string</td> <td><em>with shortest length indicator</em></td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>array</td> <td><em>see notes on optimized format</em></td> <td>array</td> <td><code>[</code></td> </tr> <trLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=c1>// function to print UBJSON's diagnostic format</span>
@@ -10,11 +19,11 @@
<span class=p>{</span>
<span class=w> </span><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=mi>32</span><span class=w> </span><span class=o>&lt;</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=k>and</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=o>&lt;</span><span class=w> </span><span class=mi>128</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=p>(</span><span class=kt>char</span><span class=p>)</span><span class=kt>byte</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>char</span><span class=o>&gt;</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>else</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=p>(</span><span class=kt>int</span><span class=p>)</span><span class=kt>byte</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
@@ -31,7 +40,7 @@
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// create an array of numbers</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>array</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=p>{</span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=mi>3</span><span class=p>,</span><span class=w> </span><span class=mi>4</span><span class=p>,</span><span class=w> </span><span class=mi>5</span><span class=p>,</span><span class=w> </span><span class=mi>6</span><span class=p>,</span><span class=w> </span><span class=mi>7</span><span class=p>,</span><span class=w> </span><span class=mi>8</span><span class=p>};</span>
@@ -48,38 +57,29 @@
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=o>&amp;</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>v_array_size</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=o>&amp;</span><span class=w> </span><span class=kt>byte</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>v_array_size_and_type</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>print_byte</span><span class=p>(</span><span class=kt>byte</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=n>i7compactTi6schemaF</span><span class=p>}</span>
<span class=p>[</span><span class=n>i1i2i3i4i5i6i7i8</span><span class=p>]</span>
<span class=p>[</span><span class=err>#</span><span class=n>i8i1i2i3i4i5i6i7i8</span>
<span class=p>[</span><span class=n>$i</span><span class=err>#</span><span class=n>i812345678</span>
</code></pre></div> </details> <h3 id=byte-layout>Byte layout<a class=headerlink href=#byte-layout title="Permanent link">&para;</a></h3> <p>Consider the following <abbr title="JavaScript Object Notation">JSON</abbr> value (shown formatted for readability):</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"id"</span><span class=p>:</span><span class=w> </span><span class=mi>300</span><span class=p>,</span>
<span class=w> </span><span class=nt>"name"</span><span class=p>:</span><span class=w> </span><span class=s2>"json"</span><span class=p>,</span>
<span class=w> </span><span class=nt>"pi"</span><span class=p>:</span><span class=w> </span><span class=mf>3.14</span><span class=p>,</span>
<span class=w> </span><span class=nt>"tags"</span><span class=p>:</span><span class=w> </span><span class=p>[</span>
<span class=w> </span><span class=s2>"a"</span><span class=p>,</span>
<span class=w> </span><span class=s2>"b"</span>
<span class=w> </span><span class=p>]</span>
<span class=p>}</span>
</code></pre></div> <p><code>to_ubjson</code> encodes it to 51 bytes (shown in hexadecimal; the encoding contains no whitespace). The colors mark the role of each byte: <span class="bl bl-t">type/marker</span> <span class="bl bl-l">length/count/size</span> <span class="bl bl-d">data</span>.</p> <div class=byte-layout markdown=0><table> <thead><tr><th>JSON</th><th>Bytes</th><th>Meaning</th></tr></thead><tbody> <tr><td><code>{</code></td><td><span class="bl bl-t">7B</span></td><td>object start (<code>{</code>)</td></tr> <tr><td><code>&quot;id&quot;: 300,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">69 64</span> <span class="bl bl-t">49</span> <span class="bl bl-d">01 2C</span></td><td>key: length 2 as int8 (<code>i</code>), then UTF-8 bytes; value: int16 (<code>I</code>), big-endian</td></tr> <tr><td><code>&quot;name&quot;: &quot;json&quot;,</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">6E 61 6D 65</span> <span class="bl bl-t">53</span> <span class="bl bl-l">69 04</span> <span class="bl bl-d">6A 73 6F 6E</span></td><td>key: length 4; value: string (<code>S</code>), length 4 as int8, UTF-8 bytes</td></tr> <tr><td><code>&quot;pi&quot;: 3.14,</code></td><td><span class="bl bl-l">69 02</span> <span class="bl bl-d">70 69</span> <span class="bl bl-t">44</span> <span class="bl bl-d">40 09 1E B8 51 EB 85 1F</span></td><td>key: length 2; value: float64 (<code>D</code>), big-endian</td></tr> <tr><td><code>&quot;tags&quot;: [</code></td><td><span class="bl bl-l">69 04</span> <span class="bl bl-d">74 61 67 73</span> <span class="bl bl-t">5B</span></td><td>key: length 4; value: array start (<code>[</code>)</td></tr> <tr><td><code>&quot;a&quot;,</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">61</span></td><td>string, length 1</td></tr> <tr><td><code>&quot;b&quot;</code></td><td><span class="bl bl-t">53</span> <span class="bl bl-l">69 01</span> <span class="bl bl-d">62</span></td><td>string, length 1</td></tr> <tr><td><code>]</code></td><td><span class="bl bl-t">5D</span></td><td>array end (<code>]</code>)</td></tr> <tr><td><code>}</code></td><td><span class="bl bl-t">7D</span></td><td>object end (<code>}</code>)</td></tr> </tbody></table></div> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Universal Binary JSON">UBJSON</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Universal Binary JSON">UBJSON</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> </tbody> </table> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>The mapping is <strong>complete</strong> in the sense that any <abbr title="Universal Binary JSON">UBJSON</abbr> value can be converted to a <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> </div> <div class="admonition warning"> <p class=admonition-title>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in string values and object keys</p> <p><abbr title="Universal Binary JSON">UBJSON</abbr>'s required string encoding is <abbr title="Unicode Transformation Format">UTF</abbr>-8, but checking it on read is opt-in: with the <a href=../../../api/basic_json/from_ubjson/ ><code>error_handler</code></a> parameter left at <code>keep</code> (the default), <code>from_ubjson()</code> accepts a string value or object key whose bytes are not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 and hands them back unchanged. Passing <code>error_handler_t::strict</code> makes <code>from_ubjson()</code> check and throw <a href=.Line truncated
</code></pre></div> </details> <h2 id=deserialization>Deserialization<a class=headerlink href=#deserialization title="Permanent link">&para;</a></h2> <p>The library maps <abbr title="Universal Binary JSON">UBJSON</abbr> types to <abbr title="JavaScript Object Notation">JSON</abbr> value types as follows:</p> <table> <thead> <tr> <th><abbr title="Universal Binary JSON">UBJSON</abbr> type</th> <th><abbr title="JavaScript Object Notation">JSON</abbr> value type</th> <th>marker</th> </tr> </thead> <tbody> <tr> <td>no-op</td> <td><em>no value, next value is read</em></td> <td><code>N</code></td> </tr> <tr> <td>null</td> <td><code>null</code></td> <td><code>Z</code></td> </tr> <tr> <td>false</td> <td><code>false</code></td> <td><code>F</code></td> </tr> <tr> <td>true</td> <td><code>true</code></td> <td><code>T</code></td> </tr> <tr> <td>float32</td> <td>number_float</td> <td><code>d</code></td> </tr> <tr> <td>float64</td> <td>number_float</td> <td><code>D</code></td> </tr> <tr> <td>uint8</td> <td>number_unsigned</td> <td><code>U</code></td> </tr> <tr> <td>int8</td> <td>number_integer</td> <td><code>i</code></td> </tr> <tr> <td>int16</td> <td>number_integer</td> <td><code>I</code></td> </tr> <tr> <td>int32</td> <td>number_integer</td> <td><code>l</code></td> </tr> <tr> <td>int64</td> <td>number_integer</td> <td><code>L</code></td> </tr> <tr> <td>string</td> <td>string</td> <td><code>S</code></td> </tr> <tr> <td>char</td> <td>string</td> <td><code>C</code></td> </tr> <tr> <td>high-precision</td> <td>number_unsigned, number_integer, or number_float</td> <td><code>H</code></td> </tr> <tr> <td>array</td> <td>array (optimized values are supported)</td> <td><code>[</code></td> </tr> <tr> <td>object</td> <td>object (optimized values are supported)</td> <td><code>{</code></td> </tr> </tbody> </table> <div class="admonition info"> <p class=admonition-title>High-precision numbers</p> <p>The payload of <code>H</code> is a length-prefixed string that is parsed as a <abbr title="JavaScript Object Notation">JSON</abbr> number (surrounding whitespace is ignored). Integer text in the range of <code>number_unsigned_t</code> (non-negative) or <code>number_integer_t</code> (negative) is stored as such; any other valid number text (larger or smaller integers, fractions, and exponents such as <code>1e2</code>) is stored as <code>number_float</code>, so precision may be lost. Text that is not a valid <abbr title="JavaScript Object Notation">JSON</abbr> number raises <a href=../../../home/exceptions/#jsonexceptionparse_error115><code>parse_error.115</code></a>, a number outside the range of <code>number_float_t</code> (<code>1e999</code>) raises <a href=../../../home/exceptions/#jsonexceptionout_of_range406><code>out_of_range.406</code></a>.</p> </div> <div class="admonition success"> <p class=admonition-title>Complete mapping</p> <p>Every well-formed <abbr title="Universal Binary JSON">UBJSON</abbr> value can be converted to a <abbr title="JavaScript Object Notation">JSON</abbr> value, with these exceptions: a high-precision number outside the range of <code>number_float_t</code> (<a href=../../../home/exceptions/#jsonexceptionout_of_range406><code>out_of_range.406</code></a>), an optimized array of <code>Z</code>, <code>T</code>, or <code>F</code> with more than 1,048,576 elements, and a count that exceeds the capacity of the container (<a href=../../../home/exceptions/#jsonexceptionout_of_range408><code>out_of_range.408</code></a>). High-precision numbers that do not fit an integer type are stored as floating-point numbers and may lose precision. Ill-formed input is rejected with a parse error.</p> </div> <div class="admonition info"> <p class=admonition-title>Duplicate object keys</p> <p>If an object contains the same key more than once, the last value is kept (the <abbr title="Universal Binary JSON">UBJSON</abbr> specification does not address duplicate keys).</p> </div> <div class="admonition info"> <p class=admonition-title>Type marker of optimized containers</p> <p>The type marker after <code>$</code> must be one of <code>Z</code>, <code>N</code>, <code>T</code>, <code>F</code>, <code>i</code>, <code>U</code>, <code>I</code>, <code>l</code>, <code>L</code>, <code>d</code>, <code>D</code>, <code>H</code>, <code>C</code>, <code>S</code>, <code>[</code>, or <code>{</code>. It is checked even if the count is 0; any other marker raises <a href=../../../home/exceptions/#jsonexceptionparse_error112><code>parse_error.112</code></a>. A counted object typed <code>N</code> (<code>{$N#i1 ...</code>) is not supported.</p> </div> <div class="admonition warning"> <p class=admonition-title>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in string values and object keys</p> <p><abbr title="Universal Binary JSON">UBJSON</abbr>'s required string encoding is <abbr title="Unicode Transformation Format">UTF</abbr>-8, but checking it on read is opt-in: with the <a href=../../../api/basic_json/from_ubjson/ ><code>error_handler</codLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
@@ -93,10 +93,10 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</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>from_ubjson</span><span class=p>(</span><span class=n>v</span><span class=p>);</span>
<span class=w> </span><span class=c1>// print the deserialized JSON value</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>2</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>2</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span>
<span class=w> </span><span class=nt>"compact"</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
<span class=w> </span><span class=nt>"schema"</span><span class=p>:</span><span class=w> </span><span class=mi>0</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 24, 2026 15:57:44 UTC">October 24, 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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+183 -166
View File
@@ -4,154 +4,11 @@ Universal Binary JSON (UBJSON) is a binary form directly imitating JSON, but req
References
- [UBJSON Website](http://ubjson.org)
- [UBJSON Website](https://ubjson.org)
## Serialization
## Byte layout
The library uses the following mapping from JSON values types to UBJSON types according to the UBJSON specification:
| JSON value type | value/range | UBJSON type | marker |
| --------------- | ----------------------------------------- | -------------- | ------ |
| null | `null` | null | `Z` |
| boolean | `true` | true | `T` |
| boolean | `false` | false | `F` |
| number_integer | -9223372036854775808..-2147483649 | int64 | `L` |
| number_integer | -2147483648..-32769 | int32 | `l` |
| number_integer | -32768..-129 | int16 | `I` |
| number_integer | -128..127 | int8 | `i` |
| number_integer | 128..255 | uint8 | `U` |
| number_integer | 256..32767 | int16 | `I` |
| number_integer | 32768..2147483647 | int32 | `l` |
| number_integer | 2147483648..9223372036854775807 | int64 | `L` |
| number_unsigned | 0..127 | int8 | `i` |
| number_unsigned | 128..255 | uint8 | `U` |
| number_unsigned | 256..32767 | int16 | `I` |
| number_unsigned | 32768..2147483647 | int32 | `l` |
| number_unsigned | 2147483648..9223372036854775807 | int64 | `L` |
| number_unsigned | 9223372036854775808..18446744073709551615 | high-precision | `H` |
| number_float | *any value* | float64 | `D` |
| string | *with shortest length indicator* | string | `S` |
| array | *see notes on optimized format* | array | `[` |
| object | *see notes on optimized format* | map | `{` |
Complete mapping
The mapping is **complete** in the sense that any JSON value type can be converted to a UBJSON value.
Any UBJSON output created by `to_ubjson` can be successfully parsed by `from_ubjson`.
Size constraints
The following values can **not** be converted to a UBJSON value:
- strings with more than 9223372036854775807 bytes (theoretical)
UTF-8 validation of string values and object keys
UBJSON's required string encoding is UTF-8. By default (the [`error_handler`](https://json.nlohmann.me/api/basic_json/to_ubjson/index.md) parameter left at `keep`), `to_ubjson()` writes the bytes of string values and object keys unchanged, even if they are not valid UTF-8. With `error_handler_t::strict`, it throws [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) for ill-formed UTF-8 instead; `replace`/`ignore` sanitize the string. [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) makes `strict` the default.
Unused UBJSON markers
The following markers are not used in the conversion:
- `Z`: no-op values are not created.
- `C`: single-byte strings are serialized with `S` markers.
NaN/infinity handling
If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the [`dump()`](https://json.nlohmann.me/api/basic_json/dump/index.md) function which serializes NaN or Infinity to `null`.
Optimized formats
The optimized formats for containers are supported: Parameter `use_size` adds size information to the beginning of a container and removes the closing marker. Parameter `use_type` further checks whether all elements of a container have the same type and adds the type marker to the beginning of the container. The `use_type` parameter must only be used together with `use_size = true`.
Note that `use_size = true` alone may result in larger representations - the benefit of this parameter is that the receiving side is immediately informed on the number of elements of the container.
An array whose type marker is `Z` (null), `T` (true) or `F` (false) stores no payload at all, because the marker already is the value. Its declared count is therefore the only thing that decides how much memory the receiving side allocates, and a handful of bytes can describe billions of elements. `from_ubjson` rejects such an array with [`out_of_range.408`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range408) when the count exceeds 1,048,576 (`1 << 20`), and `to_ubjson` writes longer arrays of these types without the annotation, so any value it produces can be read back.
Binary values
If the JSON data contains the binary type, the value stored is a list of integers, as suggested by the UBJSON documentation. In particular, this means that serialization and the deserialization of a JSON containing binary values into UBJSON and back will result in a different JSON object.
Example: serialize JSON values to UBJSON, with and without size/type optimization
```
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
// function to print UBJSON's diagnostic format
void print_byte(uint8_t byte)
{
if (32 < byte and byte < 128)
{
std::cout << (char)byte;
}
else
{
std::cout << (int)byte;
}
}
int main()
{
// create a JSON value
json j = R"({"compact": true, "schema": false})"_json;
// serialize it to UBJSON
std::vector<std::uint8_t> v = json::to_ubjson(j);
// print the vector content
for (auto& byte : v)
{
print_byte(byte);
}
std::cout << std::endl;
// create an array of numbers
json array = {1, 2, 3, 4, 5, 6, 7, 8};
// serialize it to UBJSON using default representation
std::vector<std::uint8_t> v_array = json::to_ubjson(array);
// serialize it to UBJSON using size optimization
std::vector<std::uint8_t> v_array_size = json::to_ubjson(array, true);
// serialize it to UBJSON using type optimization
std::vector<std::uint8_t> v_array_size_and_type = json::to_ubjson(array, true, true);
// print the vector contents
for (auto& byte : v_array)
{
print_byte(byte);
}
std::cout << std::endl;
for (auto& byte : v_array_size)
{
print_byte(byte);
}
std::cout << std::endl;
for (auto& byte : v_array_size_and_type)
{
print_byte(byte);
}
std::cout << std::endl;
}
```
Output:
```
{i7compactTi6schemaF}
[i1i2i3i4i5i6i7i8]
[#i8i1i2i3i4i5i6i7i8
[$i#i812345678
```
### Byte layout
UBJSON is built from just a one-byte, human-readable ASCII *type marker* (for example, `i` for int8, `S` for string, `[` for array) followed by the payload of that type. Strings and the like are prefixed with their length, which is itself a UBJSON integer value including its marker. Numbers are stored in big-endian byte order. Containers can be written in two ways: as an *unoptimized* container that is opened with `[` or `{` and closed with `]` or `}`, or as an *optimized* container that declares a count (`#`) after the opening marker, optionally preceded by an element type (`$`); an element type is only allowed together with a count. An optimized container saves the closing marker and, with a type, the per-element markers.
Consider the following JSON value (shown formatted for readability):
@@ -181,31 +38,191 @@ Consider the following JSON value (shown formatted for readability):
| `]` | 5D | array end (`]`) |
| `}` | 7D | object end (`}`) |
## Serialization
The library uses the following mapping from JSON values types to UBJSON types according to the UBJSON specification:
| JSON value type | value/range | UBJSON type | marker |
| --------------- | ----------------------------------------- | ------------------------------------------------ | --------- |
| null | `null` | null | `Z` |
| boolean | `true` | true | `T` |
| boolean | `false` | false | `F` |
| number_integer | -9223372036854775808..-2147483649 | int64 | `L` |
| number_integer | -2147483648..-32769 | int32 | `l` |
| number_integer | -32768..-129 | int16 | `I` |
| number_integer | -128..127 | int8 | `i` |
| number_integer | 128..255 | uint8 | `U` |
| number_integer | 256..32767 | int16 | `I` |
| number_integer | 32768..2147483647 | int32 | `l` |
| number_integer | 2147483648..9223372036854775807 | int64 | `L` |
| number_unsigned | 0..127 | int8 | `i` |
| number_unsigned | 128..255 | uint8 | `U` |
| number_unsigned | 256..32767 | int16 | `I` |
| number_unsigned | 32768..2147483647 | int32 | `l` |
| number_unsigned | 2147483648..9223372036854775807 | int64 | `L` |
| number_unsigned | 9223372036854775808..18446744073709551615 | high-precision | `H` |
| number_float | *any value* | float64 (float32 if `number_float_t` is `float`) | `D` (`d`) |
| string | *with shortest length indicator* | string | `S` |
| array | *see notes on optimized format* | array | `[` |
| object | *see notes on optimized format* | object | `{` |
Complete mapping
The mapping is **complete** in the sense that any JSON value type can be converted to a UBJSON value.
Any UBJSON output created by `to_ubjson` can be successfully parsed by `from_ubjson`.
Size constraints
The following values can **not** be converted to a UBJSON value:
- strings with more than 9223372036854775807 bytes (theoretical)
UTF-8 validation of string values and object keys
UBJSON's required string encoding is UTF-8. By default (the [`error_handler`](https://json.nlohmann.me/api/basic_json/to_ubjson/index.md) parameter left at `keep`), `to_ubjson()` writes the bytes of string values and object keys unchanged, even if they are not valid UTF-8. With `error_handler_t::strict`, it throws [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) for ill-formed UTF-8 instead; `replace`/`ignore` sanitize the string. [`JSON_STRICT_BINARY_UTF8`](https://json.nlohmann.me/api/macros/json_strict_binary_utf8/index.md) makes `strict` the default.
Unused UBJSON markers
The following markers are not used in the conversion:
- `N`: no-op values are never written (they are skipped when reading).
- `C`: single-byte strings are serialized with `S` markers.
NaN/infinity handling
NaN and infinity are written as IEEE 754 float64 values (`D`) and read back unchanged. This differs from [`dump()`](https://json.nlohmann.me/api/basic_json/dump/index.md), which serializes them to `null`, and from the UBJSON specification, which encodes infinity as `null` (it does not mention NaN); other UBJSON readers may therefore not accept these values.
Optimized formats
The optimized formats for containers are supported: Parameter `use_size` adds size information to the beginning of a container and removes the closing marker. Parameter `use_type` further checks whether all elements of a container have the same type and adds the type marker to the beginning of the container. The `use_type` parameter must only be used together with `use_size = true`: combining `use_type` with `use_size = false` throws [`other_error.502`](https://json.nlohmann.me/home/exceptions/#jsonexceptionother_error502) if the value contains a non-empty array, object, or binary value.
Two elements have the same type if they are written with the same type marker. For example, `[1, 2]` is written with the type `i`, but `[1, 200]` (`i`, `U`), `[true, false]` (`T`, `F`), and `[1, 2.5]` (`i`, `D`) are not; an empty container is never given a `$` annotation of its own (an array of empty arrays is still typed `[`).
Note that `use_size = true` alone may result in larger representations - the benefit of this parameter is that the receiving side is immediately informed on the number of elements of the container.
An array whose type marker is `Z` (null), `T` (true) or `F` (false) stores no payload at all, because the marker already is the value. Its declared count is therefore the only thing that decides how much memory the receiving side allocates, and a handful of bytes can describe billions of elements. `from_ubjson` rejects such an array with [`out_of_range.408`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range408) when the count exceeds 1,048,576 (`1 << 20`), and `to_ubjson` writes longer arrays of these types in the counted but untyped form: the `$` type marker is dropped, the `#` count is kept, and every element is written with its own marker (`[#l 1048577 Z Z ...`), so any value it produces can be read back. Objects and untyped counted arrays are not subject to this limit.
Binary values
If the JSON data contains the binary type, the value stored is a list of integers, as suggested by the UBJSON documentation. In particular, this means that serialization and the deserialization of a JSON containing binary values into UBJSON and back will result in a different JSON object.
Example: serialize JSON values to UBJSON, with and without size/type optimization
```
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using nlohmann::json;
using namespace nlohmann::literals;
// function to print UBJSON's diagnostic format
void print_byte(uint8_t byte)
{
if (32 < byte and byte < 128)
{
std::cout << static_cast<char>(byte);
}
else
{
std::cout << static_cast<int>(byte);
}
}
int main()
{
// create a JSON value
json j = R"({"compact": true, "schema": false})"_json;
// serialize it to UBJSON
std::vector<std::uint8_t> v = json::to_ubjson(j);
// print the vector content
for (auto& byte : v)
{
print_byte(byte);
}
std::cout << '\n';
// create an array of numbers
json array = {1, 2, 3, 4, 5, 6, 7, 8};
// serialize it to UBJSON using default representation
std::vector<std::uint8_t> v_array = json::to_ubjson(array);
// serialize it to UBJSON using size optimization
std::vector<std::uint8_t> v_array_size = json::to_ubjson(array, true);
// serialize it to UBJSON using type optimization
std::vector<std::uint8_t> v_array_size_and_type = json::to_ubjson(array, true, true);
// print the vector contents
for (auto& byte : v_array)
{
print_byte(byte);
}
std::cout << '\n';
for (auto& byte : v_array_size)
{
print_byte(byte);
}
std::cout << '\n';
for (auto& byte : v_array_size_and_type)
{
print_byte(byte);
}
std::cout << '\n';
}
```
Output:
```
{i7compactTi6schemaF}
[i1i2i3i4i5i6i7i8]
[#i8i1i2i3i4i5i6i7i8
[$i#i812345678
```
## Deserialization
The library maps UBJSON types to JSON value types as follows:
| UBJSON type | JSON value type | marker |
| ----------- | --------------------------------------- | ------ |
| no-op | *no value, next value is read* | `N` |
| null | `null` | `Z` |
| false | `false` | `F` |
| true | `true` | `T` |
| float32 | number_float | `d` |
| float64 | number_float | `D` |
| uint8 | number_unsigned | `U` |
| int8 | number_integer | `i` |
| int16 | number_integer | `I` |
| int32 | number_integer | `l` |
| int64 | number_integer | `L` |
| string | string | `S` |
| char | string | `C` |
| array | array (optimized values are supported) | `[` |
| object | object (optimized values are supported) | `{` |
| UBJSON type | JSON value type | marker |
| -------------- | ------------------------------------------------ | ------ |
| no-op | *no value, next value is read* | `N` |
| null | `null` | `Z` |
| false | `false` | `F` |
| true | `true` | `T` |
| float32 | number_float | `d` |
| float64 | number_float | `D` |
| uint8 | number_unsigned | `U` |
| int8 | number_integer | `i` |
| int16 | number_integer | `I` |
| int32 | number_integer | `l` |
| int64 | number_integer | `L` |
| string | string | `S` |
| char | string | `C` |
| high-precision | number_unsigned, number_integer, or number_float | `H` |
| array | array (optimized values are supported) | `[` |
| object | object (optimized values are supported) | `{` |
High-precision numbers
The payload of `H` is a length-prefixed string that is parsed as a JSON number (surrounding whitespace is ignored). Integer text in the range of `number_unsigned_t` (non-negative) or `number_integer_t` (negative) is stored as such; any other valid number text (larger or smaller integers, fractions, and exponents such as `1e2`) is stored as `number_float`, so precision may be lost. Text that is not a valid JSON number raises [`parse_error.115`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error115), a number outside the range of `number_float_t` (`1e999`) raises [`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406).
Complete mapping
The mapping is **complete** in the sense that any UBJSON value can be converted to a JSON value.
Every well-formed UBJSON value can be converted to a JSON value, with these exceptions: a high-precision number outside the range of `number_float_t` ([`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406)), an optimized array of `Z`, `T`, or `F` with more than 1,048,576 elements, and a count that exceeds the capacity of the container ([`out_of_range.408`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range408)). High-precision numbers that do not fit an integer type are stored as floating-point numbers and may lose precision. Ill-formed input is rejected with a parse error.
Duplicate object keys
If an object contains the same key more than once, the last value is kept (the UBJSON specification does not address duplicate keys).
Type marker of optimized containers
The type marker after `$` must be one of `Z`, `N`, `T`, `F`, `i`, `U`, `I`, `l`, `L`, `d`, `D`, `H`, `C`, `S`, `[`, or `{`. It is checked even if the count is 0; any other marker raises [`parse_error.112`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112). A counted object typed `N` (`{$N#i1 ...`) is not supported.
Ill-formed UTF-8 in string values and object keys
@@ -218,7 +235,7 @@ Example: deserialize a JSON value from UBJSON
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using nlohmann::json;
int main()
{
@@ -232,7 +249,7 @@ int main()
json j = json::from_ubjson(v);
// print the deserialized JSON value
std::cout << std::setw(2) << j << std::endl;
std::cout << std::setw(2) << j << '\n';
}
```