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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/api/basic_json/string_t/ rel = canonical > < link href = ../size/ rel = prev > < link href = ../swap/ rel = next > < link rel = icon href = ../../../assets/images/favicon.png > < meta name = generator content = "mkdocs-1.5.3, mkdocs-material-9.4.7" > < title > string_t - JSON for Modern C++< / title > < link rel = stylesheet href = ../../../assets/stylesheets/main.4b4a2bd9.min.css > < link rel = stylesheet href = ../../../assets/stylesheets/palette.356b1318.min.css > < link rel = preconnect href = https://fonts.gstatic.com crossorigin > < link rel = stylesheet href = "https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CJetBrains+Mono:400,400i,700,700i&display=fallback" > < 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 > < script > var palette = _ _md _get ( "__palette" ) ; if ( palette && "object" == typeof palette . color ) for ( var key of Object . keys ( palette . color ) ) document . body . setAttribute ( "data-md-color-" + key , palette . color [ key ] ) < / script > < 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 = #nlohmannbasic_jsonstring_t 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 3.54Z" / > < / 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 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2Z" / > < / 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 > string_t < / 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_1 > < label class = "md-header__button md-icon" title = "Switch to dark mode" for = __palette_2 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 12 20 8.69Z" / > < / 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_2 > < label class = "md-header__button md-icon" title = "Switch to light mode" for = __palette_1 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 12c
< / code > < / pre > < / div > < p > The type used to store JSON strings.< / p > < p > < a href = https://tools.ietf.org/html/rfc8259 > RFC 8259< / a > describes JSON strings as follows:< / p > < blockquote > < p > A string is a sequence of zero or more Unicode characters.< / p > < / blockquote > < p > To store objects in C++, a type is defined by the template parameter described below. Unicode values are split by the JSON class into byte-sized characters during deserialization.< / p > < h2 id = template-parameters > Template parameters< a class = headerlink href = #template-parameters title = "Permanent link" > ¶ < / a > < / h2 > < dl > < dt > < code > StringType< / code > < / dt > < dd > the container to store strings (e.g., < code > std::string< / code > ). Note this container is used for keys/names in objects, see < a href = ../object_t/ > object_t< / a > .< / dd > < / dl > < h2 id = notes > Notes< a class = headerlink href = #notes title = "Permanent link" > ¶ < / a > < / h2 > < h4 id = default-type > Default type< a class = headerlink href = #default-type title = "Permanent link" > ¶ < / a > < / h4 > < p > With the default values for < code > StringType< / code > (< 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 > < h4 id = encoding > Encoding< a class = headerlink href = #encoding title = "Permanent link" > ¶ < / a > < / h4 > < p > Strings are stored in UTF-8 encoding. Therefore, functions like < code > std::string::size()< / code > or < code > std::string::length()< / code > return the number of bytes in the string rather than the number of characters or glyphs.< / p > < h4 id = string-comparison > String comparison< a class = headerlink href = #string-comparison title = "Permanent link" > ¶ < / a > < / h4 > < p > < a href = https://tools.ietf.org/html/rfc8259 > RFC 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 > < h4 id = storage > Storage< a class = headerlink href = #storage title = "Permanent link" > ¶ < / a > < / h4 > < 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 = examples > Examples< a class = headerlink href = #examples title = "Permanent link" > ¶ < / a > < / h2 > < details class = example > < summary > Example< / summary > < p > The following code shows that < code > string_t< / code > is by default, a typedef to < code class = highlight > < span class = n > std< / span > < span class = o > ::< / span > < span class = n > string< / span > < / code > .< / p > < div class = highlight > < pre > < span > < / span > < code > < span class = cp > #include< / span > < span class = w > < / span > < span class = cpf > < iostream> < / span >
< span class = cp > #include< / span > < span class = w > < / span > < span class = cpf > < iomanip> < / span >
< span class = cp > #include< / span > < span class = w > < / span > < span class = cpf > < nlohmann/json.hpp> < / span >
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< 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 >
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< span class = kt > int< / span > < span class = w > < / span > < span class = nf > main< / span > < span class = p > ()< / 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 > < < < / span > < span class = w > < / span > < span class = n > std< / span > < span class = o > ::< / span > < span class = n > boolalpha< / span > < span class = w > < / span > < span class = o > < < < / span > < span class = w > < / span > < span class = n > std< / span > < span class = o > ::< / span > < span class = n > is_same< / span > < span class = o > < < / span > < span class = n > std< / span > < span class = o > ::< / span > < span class = n > string< / span > < span class = p > ,< / span > < span class = w > < / span > < span class = n > json< / span > < span class = o > ::< / span > < span class = n > string_t< / span > < span class = o > > ::< / span > < span class = n > value< / span > < span class = w > < / span > < span class = o > < < < / 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 = p > }< / span >
< / code > < / pre > < / div > < p > Output:< / p > < div class = highlight > < pre > < span > < / span > < code > < span class = kc > true< / span >
< / code > < / pre > < / div > < / details > < h2 id = version-history > Version history< a class = headerlink href = #version-history title = "Permanent link" > ¶ < / a > < / h2 > < ul > < li > Added in version 1.0.0.< / li > < / ul > < hr > < div class = md-source-file > < small > Last update: < span class = "git-revision-date-localized-plugin git-revision-date-localized-plugin-date" > May 1, 2022< / span > < / small > < / div > < / article > < / div > < script > var tabs = _ _md _get ( "__tabs" ) ; if ( Array . isArray ( tabs ) ) e : for ( var set of document . querySelectorAll ( ".tabbed-set" ) ) { var tab , labels = set . querySelector ( ".tabbed-labels" ) ; for ( 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 > < / 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 8v12Z" / > < / 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 - 2023 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 0 496 512" > <!-- Font Awesome Free 6.4.2 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2023 Fonticons, Inc. --> < path d = "M165.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6zm-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3zm44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9zM244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8zM97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1zm-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7zm32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1zm-11.4-14.7c-1.6 1-1.6 3.6 0 5.9 1.6 2.3 4.3 3.3 5.6 2.3 1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2z" / > < / svg > < / a > < a href = https://twitter.com/nlohmann target = _blank rel = noopener title = twitter.com class = md-social__link > < svg xmlns = http://www.w3.org/2000/svg viewbox = "0 0 512 512" > <!-- Font Awesome Free 6.4.2 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2023 Fonticons, Inc. --> < path d = "M459.37 151 . 716c . 325 4 . 548 . 325 9 . 097 . 325 13 . 645 0 138 . 72-105 . 583 298 . 558-298 . 558 298 . 558-59 . 452 0-114 . 68-17 . 219-161 . 137-47 . 106 8 . 447 . 974 16 . 568 1 . 299 25 . 34 1 . 299 49 . 055 0 94 . 213-16 . 568 130 . 274-44 . 832-46 . 132- . 975-84 . 792-31 . 188-98 . 112-72 . 772 6 . 498 . 974 12 . 995 1 . 624 19 . 818 1 . 624 9 . 421 0 18 . 843-1 . 3 27 . 614-3 . 573-48 . 081-9 . 747-84 . 143-51 . 98-84 . 143-102 . 985v-1 . 299c13 . 969 7 . 797 30 . 214 12 . 67 47 . 431 13 . 319-28 . 264-18 . 843-46 . 781-51 . 005-46 . 781-87 . 391 0-19 . 492 5 . 197-37 . 36 14 . 294-52 . 954 51 . 655 63 . 675 129 . 3 105 . 258 216 . 365 109 . 807-1 . 624-7 . 797-2 . 599-15 . 918-2 . 599-24 . 04 0-57 . 828 46 . 782-104 . 934 104 . 934-104 . 934 30 . 213 0 57 . 502 12 . 67 76 . 67 33 . 137 23 . 715-4 . 548 46 . 456-13 . 32 66 . 599-25 . 34-7 . 798 24 . 366-24 . 366 44 . 833-46 . 132 57 . 827 21 . 117-2 . 273 41 . 584-8 . 122 60 . 426-16 . 243-14 . 292 20 . 7
