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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/accept/ rel = canonical > < link href = ../~basic_json/ rel = prev > < link href = ../array/ rel = next > < link rel = icon href = ../../../assets/images/favicon.png > < meta name = generator content = "mkdocs-1.5.3, mkdocs-material-9.4.7" > < title > accept - 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_jsonaccept 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 > accept < / 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
< span class = k > template< / span > < span class = o > < < / span > < span class = k > typename< / span > < span class = w > < / span > < span class = nc > InputType< / span > < span class = o > > < / span >
< span class = k > static< / span > < span class = w > < / span > < span class = kt > bool< / span > < span class = w > < / span > < span class = n > accept< / span > < span class = p > (< / span > < span class = n > InputType< / span > < span class = o > & & < / span > < span class = w > < / span > < span class = n > i< / span > < span class = p > ,< / span >
< span class = w > < / span > < span class = k > const< / span > < span class = w > < / span > < span class = kt > bool< / span > < span class = w > < / span > < span class = n > ignore_comments< / span > < span class = w > < / span > < span class = o > =< / span > < span class = w > < / span > < span class = nb > false< / span > < span class = p > );< / span >
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< span class = c1 > // (2)< / span >
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< span class = k > template< / span > < span class = o > < < / span > < span class = k > typename< / span > < span class = w > < / span > < span class = nc > IteratorType< / span > < span class = o > > < / span >
< span class = k > static< / span > < span class = w > < / span > < span class = kt > bool< / span > < span class = w > < / span > < span class = n > accept< / span > < span class = p > (< / span > < span class = n > IteratorType< / span > < span class = w > < / span > < span class = n > first< / span > < span class = p > ,< / span > < span class = w > < / span > < span class = n > IteratorType< / span > < span class = w > < / span > < span class = n > last< / span > < span class = p > ,< / span >
< span class = w > < / span > < span class = k > const< / span > < span class = w > < / span > < span class = kt > bool< / span > < span class = w > < / span > < span class = n > ignore_comments< / span > < span class = w > < / span > < span class = o > =< / span > < span class = w > < / span > < span class = nb > false< / span > < span class = p > );< / span >
< / code > < / pre > < / div > < p > Checks whether the input is valid JSON.< / p > < ol > < li > Reads from a compatible input.< / li > < li > < p > Reads from a pair of character iterators< / p > < p > The value_type of the iterator must be an integral type with size of 1, 2 or 4 bytes, which will be interpreted respectively as UTF-8, UTF-16 and UTF-32.< / p > < / li > < / ol > < p > Unlike the < a href = ../parse/ > < code > parse< / code > < / a > function, this function neither throws an exception in case of invalid JSON input (i.e., a parse error) nor creates diagnostic information.< / p > < h2 id = template-parameters > Template parameters< a class = headerlink href = #template-parameters title = "Permanent link" > ¶ < / a > < / h2 > < dl > < dt > < code > InputType< / code > < / dt > < dd > < p > A compatible input, for instance:< / p > < ul > < li > an < code > std::istream< / code > object< / li > < li > a < code > FILE< / code > pointer (must not be null)< / li > < li > a C-style array of characters< / li > < li > a pointer to a null-terminated string of single byte characters< / li > < li > a < code > std::string< / code > < / li > < li > an object < code > obj< / code > for which < code > begin(obj)< / code > and < code > end(obj)< / code > produces a valid pair of iterators.< / li > < / ul > < / dd > < dt > < code > IteratorType< / code > < / dt > < dd > < p > a compatible iterator type, for instance.< / p > < ul > < li > a pair of < code > std::string::iterator< / code > or < code > std::vector< std::uint8_t> ::iterator< / code > < / li > < li > a pair of pointers such as < code > ptr< / code > and < code > ptr + len< / code > < / li > < / ul > < / dd > < / dl > < h2 id = parameters > Parameters< a class = headerlink href = #parameters title = "Permanent link" > ¶ < / a > < / h2 > < dl > < dt > < code > i< / code > (in)< / dt > < dd > Input to parse from.< / dd > < dt > < code > ignore_comments< / code > (in)< / dt > < dd > whether comments should be ignored and treated like whitespace (< code class = highlight > < span class = nb > true< / span > < / code > ) or yield a parse error (< code class = highlight > < span class = nb > false< / span > < / code > ); (optional, < code class = highlight > < span class = nb > false< / span > < / code > by default)< / dd > < dt > < code > first< / code > (in)< / dt > < dd > iterator to start of character range< / dd > < dt > < code > last< / code > (in)< / dt > < dd > iterator to end of character range< / dd > < / dl > < h2 id = return-value > Return value< a class = headerlink href = #return-value title = "Permanent link" > ¶ < / a > < / h2 > < p > Whether the input is valid JSON.< / p > < h2 id = exception-safety > Exception safety< a class = headerlink href = #exception-safety title = "Permanent link" > ¶ < / a > < / h2 > < p > Strong guarantee: if an exception is thrown, there are no changes in the JSON value.< / p > < h2 id = complexity > Complexity< a class = headerlink href = #complexity title = "Permanent link" > ¶ < / a > < / h2 > < p > Linear in the length of the input. The parser is a predictive LL(1) parser.< / p > < h2 id = notes > Notes< a class = headerlink href = #notes title = "Permanent link" > ¶ < / a > < / h2 > < p > (1) A UTF-8 byte order mark is silently ignored.< / p > < div class = "admonition danger" > < p class = admonition-title > Runtime assertion< / p > < p > The precondition that a passed < code class = highlight > < span class = kt > FILE< / span > < / code > pointer must not be null is enforced with a < a href = ../../../features/assertions/ > runtime assertion< / a > .< / p > < / div > < h2 id = examples > Examples< a class = headerlink href = #examples title = "Permanent link" > ¶ < / a > < / h2 > < details class = example > < summary > Example< / summary > < p > The example below demonstrates the < code > accept()< / code > function reading from a string.< / 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 >
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< span class = w > < / span > < span class = c1 > // a valid JSON text< / span >
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< span class = w > < / span > < span class = k > auto< / span > < span class = w > < / span > < span class = n > valid_text< / span > < span class = w > < / span > < span class = o > =< / span > < span class = w > < / span > < span class = sa > R< / span > < span class = s > " < / span > < span class = dl > (< / span >
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< span class = s > {< / span >
< span class = s > " numbers" : [1, 2, 3]< / span >
< span class = s > }< / span >
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< span class = s > < / span > < span class = dl > )< / span > < span class = s > " < / span > < span class = p > ;< / span >
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< span class = w > < / span > < span class = c1 > // an invalid JSON text< / span >
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< span class = w > < / span > < span class = k > auto< / span > < span class = w > < / span > < span class = n > invalid_text< / span > < span class = w > < / span > < span class = o > =< / span > < span class = w > < / span > < span class = sa > R< / span > < span class = s > " < / span > < span class = dl > (< / span >
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< span class = s > {< / span >
< span class = s > " strings" : [" extra" , " comma" , ]< / span >
< span class = s > }< / span >
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< span class = s > < / span > < span class = dl > )< / span > < span class = s > " < / span > < span class = p > ;< / span >
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< 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 > json< / span > < span class = o > ::< / span > < span class = n > accept< / span > < span class = p > (< / span > < span class = n > valid_text< / span > < span class = p > )< / span > < span class = w > < / span > < span class = o > < < < / span > < span class = w > < / span > < span class = sc > ' ' < / 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 > accept< / span > < span class = p > (< / span > < span class = n > invalid_text< / span > < span class = p > )< / span > < span class = w > < / span > < span class = o > < < < / 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 = kc > true< / span > < span class = w > < / span > < span class = kc > false< / span >
< / code > < / pre > < / div > < / details > < h2 id = see-also > See also< a class = headerlink href = #see-also title = "Permanent link" > ¶ < / a > < / h2 > < ul > < li > < a href = ../parse/ > parse< / a > - deserialize from a compatible input< / li > < li > < a href = ../../operator_gtgt/ > operator> > < / a > - deserialize from stream< / li > < / ul > < h2 id = version-history > Version history< a class = headerlink href = #version-history title = "Permanent link" > ¶ < / a > < / h2 > < ul > < li > Added in version 3.0.0.< / li > < li > Ignoring comments via < code > ignore_comments< / code > added in version 3.9.0.< / li > < / ul > < div class = "admonition warning" > < p class = admonition-title > Deprecation< / p > < p > Overload (2) replaces calls to < code > accept< / code > with a pair of iterators as their first parameter which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like < code class = highlight > < span class = n > accept< / span > < span class = p > ({< / span > < span class = n > ptr< / span > < span class = p > ,< / span > < span class = w > < / span > < span class = n > ptr< / span > < span class = o > +< / span > < span class = n > len< / span > < span class = p > },< / span > < span class = w > < / span > < span class = p > ...);< / span > < / code > with < code class = highlight > < span class = n > accept< / span > < span class = p > (< / span > < span class = n > ptr< / span > < span class = p > ,< / span > < span class = w > < / span > < span class = n > ptr< / span > < span class = o > +< / span > < span class = n > len< / span > < span class = p > ,< / span > < span class = w > < / span > < span class = p > ...);< / span > < / code > .< / p > < p > You should be warned by your compiler with a < code > -Wdeprecated-declarations< / code > warning if you are using a deprecated function.< / p > < / div > < hr > < div class = md-source-file > < small > Last update: < span class = "git-revision-date-localized-plugin git-revision-date-localized-plugin-date" > July 28, 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-
