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json/include/nlohmann/detail/output/serializer.hpp
T
Niels Lohmann ccb290facf Reduce the string_t and array_t members the library requires 
Several members were required only because of how the library happened to
be written, not because the functionality needs them. Dropping them widens
the set of usable string and array types, and one of them was also a
performance problem.

string_t:

- c_str() is gone. Every call site already knew the length and passed it
  along, so data() is enough. The one place that did not, the diagnostics
  path in exceptions.hpp, now builds the token from data() and size(),
  which also stops it from truncating keys that contain a null byte.
- back() is gone; the serializer indexes the last character instead.
- find(str, pos), replace(), and substr() are gone. escape() and
  unescape() rebuilt the string with one replace() per escaped character,
  which moves the tail every time: escaping a string of n characters that
  all need escaping cost O(n^2). Both now scan with find_first_of() -- a
  member the pointer parser already required -- and append whole runs, so
  the common case is one search and one copy. Escaping 64000 tildes drops
  from 717 ms to 20 ms; a string with nothing to escape gets faster too
  (8.4 ms to 5.8 ms), because the scan is still a single memchr per pass.
  json_pointer::split() takes its reference tokens with the
  (const char*, size_type) constructor rather than substr().
- json_pointer::to_string() accumulates with concat<string_t> instead of
  letting concat default to std::string and converting afterwards, so
  streaming a json_pointer no longer requires string_t to be assignable
  from a std::string.

array_t:

- at(size_type) is gone. basic_json::at(size_type) checked the index by
  calling array_t::at() and translating std::out_of_range, which also
  required the array type to throw that exact exception. It now compares
  against size() and uses operator[]. The thrown exception, its message,
  and the behaviour under JSON_NOEXCEPTION are unchanged.

The BSON writer wrote the terminating null byte out of the string's own
buffer (size() + 1). It now writes the byte itself, so string_t::data()
need not be null-terminated for to_bson().

The tests pin the reduced API: alt_string loses the five dropped members
and gains coverage of the escaping paths, and a std::vector whose at() is
hidden is used as an ArrayType.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-08-28 17:38:58 +00:00

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// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2008, 2009 Björn Hoehrmann <bjoern@hoehrmann.de>
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
#pragma once
#include <algorithm> // reverse, remove, fill, find, none_of
#include <array> // array
#include <clocale> // localeconv, lconv
#include <cmath> // labs, isfinite, isnan, signbit
#include <cstddef> // size_t, ptrdiff_t
#include <cstdint> // uint8_t
#include <cstdio> // snprintf
#include <limits> // numeric_limits
#include <string> // string, char_traits
#include <iomanip> // setfill, setw
#include <type_traits> // is_same
#include <utility> // move
#include <nlohmann/detail/conversions/to_chars.hpp>
#include <nlohmann/detail/exceptions.hpp>
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/meta/cpp_future.hpp>
#include <nlohmann/detail/output/binary_writer.hpp>
#include <nlohmann/detail/output/output_adapters.hpp>
#include <nlohmann/detail/string_concat.hpp>
#include <nlohmann/detail/value_t.hpp>
NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{
///////////////////
// serialization //
///////////////////
/// how to treat decoding errors
enum class error_handler_t
{
strict, ///< throw a type_error exception in case of invalid UTF-8
replace, ///< replace invalid UTF-8 sequences with U+FFFD
ignore ///< ignore invalid UTF-8 sequences
};
template<typename BasicJsonType>
class serializer
{
using string_t = typename BasicJsonType::string_t;
using number_float_t = typename BasicJsonType::number_float_t;
using number_integer_t = typename BasicJsonType::number_integer_t;
using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
using binary_char_t = typename BasicJsonType::binary_t::value_type;
static constexpr std::uint8_t UTF8_ACCEPT = 0;
static constexpr std::uint8_t UTF8_REJECT = 1;
public:
/*!
@param[in] s output stream to serialize to
@param[in] ichar indentation character to use
@param[in] error_handler_ how to react on decoding errors
*/
serializer(output_adapter_t<char> s, const char ichar,
error_handler_t error_handler_ = error_handler_t::strict)
: o(std::move(s))
, loc(std::localeconv())
, thousands_sep(loc->thousands_sep == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->thousands_sep)))
, decimal_point(loc->decimal_point == nullptr ? '\0' : std::char_traits<char>::to_char_type(* (loc->decimal_point)))
, indent_char(ichar)
, indent_string(512, indent_char)
, error_handler(error_handler_)
{}
// deleted because of pointer members
serializer(const serializer&) = delete;
serializer& operator=(const serializer&) = delete;
serializer(serializer&&) = delete;
serializer& operator=(serializer&&) = delete;
~serializer() = default;
/*!
@brief internal implementation of the serialization function
This function is called by the public member function dump and organizes
the serialization internally. The indentation level is propagated as
additional parameter. In case of arrays and objects, the function is
called recursively.
- strings and object keys are escaped using `escape_string()`
- integer numbers are converted implicitly via `operator<<`
- floating-point numbers are converted to a string using `"%g"` format
- binary values are serialized as objects containing the subtype and the
byte array
@param[in] val value to serialize
@param[in] pretty_print whether the output shall be pretty-printed
@param[in] ensure_ascii If @a ensure_ascii is true, all non-ASCII characters
in the output are escaped with `\uXXXX` sequences, and the result consists
of ASCII characters only.
@param[in] indent_step the indent level
@param[in] current_indent the current indent level (only used internally)
*/
void dump(const BasicJsonType& val,
const bool pretty_print,
const bool ensure_ascii,
const unsigned int indent_step,
const unsigned int current_indent = 0)
{
switch (val.m_data.m_type)
{
case value_t::object:
{
if (val.m_data.m_value.object->empty())
{
o->write_characters("{}", 2);
return;
}
if (pretty_print)
{
o->write_characters("{\n", 2);
// variable to hold indentation for recursive calls
const auto new_indent = current_indent + indent_step;
if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
{
indent_string.resize(indent_string.size() * 2, ' ');
}
// first n-1 elements
auto i = val.m_data.m_value.object->cbegin();
for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
{
o->write_characters(indent_string.data(), new_indent);
o->write_character('\"');
dump_escaped(i->first, ensure_ascii);
o->write_characters("\": ", 3);
dump(i->second, true, ensure_ascii, indent_step, new_indent);
o->write_characters(",\n", 2);
}
// last element
JSON_ASSERT(i != val.m_data.m_value.object->cend());
JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
o->write_characters(indent_string.data(), new_indent);
o->write_character('\"');
dump_escaped(i->first, ensure_ascii);
o->write_characters("\": ", 3);
dump(i->second, true, ensure_ascii, indent_step, new_indent);
o->write_character('\n');
o->write_characters(indent_string.data(), current_indent);
o->write_character('}');
}
else
{
o->write_character('{');
// first n-1 elements
auto i = val.m_data.m_value.object->cbegin();
for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
{
o->write_character('\"');
dump_escaped(i->first, ensure_ascii);
o->write_characters("\":", 2);
dump(i->second, false, ensure_ascii, indent_step, current_indent);
o->write_character(',');
}
// last element
JSON_ASSERT(i != val.m_data.m_value.object->cend());
JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
o->write_character('\"');
dump_escaped(i->first, ensure_ascii);
o->write_characters("\":", 2);
dump(i->second, false, ensure_ascii, indent_step, current_indent);
o->write_character('}');
}
return;
}
case value_t::array:
{
if (val.m_data.m_value.array->empty())
{
o->write_characters("[]", 2);
return;
}
if (pretty_print)
{
o->write_characters("[\n", 2);
// variable to hold indentation for recursive calls
const auto new_indent = current_indent + indent_step;
if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
{
indent_string.resize(indent_string.size() * 2, ' ');
}
// first n-1 elements
for (auto i = val.m_data.m_value.array->cbegin();
i != val.m_data.m_value.array->cend() - 1; ++i)
{
o->write_characters(indent_string.data(), new_indent);
dump(*i, true, ensure_ascii, indent_step, new_indent);
o->write_characters(",\n", 2);
}
// last element
JSON_ASSERT(!val.m_data.m_value.array->empty());
o->write_characters(indent_string.data(), new_indent);
dump(val.m_data.m_value.array->back(), true, ensure_ascii, indent_step, new_indent);
o->write_character('\n');
o->write_characters(indent_string.data(), current_indent);
o->write_character(']');
}
else
{
o->write_character('[');
// first n-1 elements
for (auto i = val.m_data.m_value.array->cbegin();
i != val.m_data.m_value.array->cend() - 1; ++i)
{
dump(*i, false, ensure_ascii, indent_step, current_indent);
o->write_character(',');
}
// last element
JSON_ASSERT(!val.m_data.m_value.array->empty());
dump(val.m_data.m_value.array->back(), false, ensure_ascii, indent_step, current_indent);
o->write_character(']');
}
return;
}
case value_t::string:
{
o->write_character('\"');
dump_escaped(*val.m_data.m_value.string, ensure_ascii);
o->write_character('\"');
return;
}
case value_t::binary:
{
if (pretty_print)
{
o->write_characters("{\n", 2);
// variable to hold indentation for recursive calls
const auto new_indent = current_indent + indent_step;
if (JSON_HEDLEY_UNLIKELY(indent_string.size() < new_indent))
{
indent_string.resize(indent_string.size() * 2, ' ');
}
o->write_characters(indent_string.data(), new_indent);
o->write_characters("\"bytes\": [", 10);
if (!val.m_data.m_value.binary->empty())
{
for (auto i = val.m_data.m_value.binary->cbegin();
i != val.m_data.m_value.binary->cend() - 1; ++i)
{
dump_integer(to_byte_value(*i));
o->write_characters(", ", 2);
}
dump_integer(to_byte_value(val.m_data.m_value.binary->back()));
}
o->write_characters("],\n", 3);
o->write_characters(indent_string.data(), new_indent);
o->write_characters("\"subtype\": ", 11);
if (val.m_data.m_value.binary->has_subtype())
{
dump_integer(val.m_data.m_value.binary->subtype());
}
else
{
o->write_characters("null", 4);
}
o->write_character('\n');
o->write_characters(indent_string.data(), current_indent);
o->write_character('}');
}
else
{
o->write_characters("{\"bytes\":[", 10);
if (!val.m_data.m_value.binary->empty())
{
for (auto i = val.m_data.m_value.binary->cbegin();
i != val.m_data.m_value.binary->cend() - 1; ++i)
{
dump_integer(to_byte_value(*i));
o->write_character(',');
}
dump_integer(to_byte_value(val.m_data.m_value.binary->back()));
}
o->write_characters("],\"subtype\":", 12);
if (val.m_data.m_value.binary->has_subtype())
{
dump_integer(val.m_data.m_value.binary->subtype());
o->write_character('}');
}
else
{
o->write_characters("null}", 5);
}
}
return;
}
case value_t::boolean:
{
if (val.m_data.m_value.boolean)
{
o->write_characters("true", 4);
}
else
{
o->write_characters("false", 5);
}
return;
}
case value_t::number_integer:
{
dump_integer(val.m_data.m_value.number_integer);
return;
}
case value_t::number_unsigned:
{
dump_integer(val.m_data.m_value.number_unsigned);
return;
}
case value_t::number_float:
{
dump_float(val.m_data.m_value.number_float);
return;
}
case value_t::discarded:
{
o->write_characters("<discarded>", 11);
return;
}
case value_t::null:
{
o->write_characters("null", 4);
return;
}
default: // LCOV_EXCL_LINE
JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
}
}
JSON_PRIVATE_UNLESS_TESTED:
/*!
@brief dump escaped string
Escape a string by replacing certain special characters by a sequence of an
escape character (backslash) and another character and other control
characters by a sequence of "\u" followed by a four-digit hex
representation. The escaped string is written to output stream @a o.
@param[in] s the string to escape
@param[in] ensure_ascii whether to escape non-ASCII characters with
\uXXXX sequences
@complexity Linear in the length of string @a s.
*/
void dump_escaped(const string_t& s, const bool ensure_ascii)
{
std::uint32_t codepoint{};
std::uint8_t state = UTF8_ACCEPT;
std::size_t bytes = 0; // number of bytes written to string_buffer
// number of bytes written at the point of the last valid byte
std::size_t bytes_after_last_accept = 0;
std::size_t undumped_chars = 0;
for (std::size_t i = 0; i < s.size(); ++i)
{
const auto byte = static_cast<std::uint8_t>(s[i]);
switch (decode(state, codepoint, byte))
{
case UTF8_ACCEPT: // decode found a new code point
{
switch (codepoint)
{
case 0x08: // backspace
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = 'b';
break;
}
case 0x09: // horizontal tab
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = 't';
break;
}
case 0x0A: // newline
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = 'n';
break;
}
case 0x0C: // formfeed
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = 'f';
break;
}
case 0x0D: // carriage return
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = 'r';
break;
}
case 0x22: // quotation mark
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = '\"';
break;
}
case 0x5C: // reverse solidus
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = '\\';
break;
}
default:
{
// escape control characters (0x00..0x1F) or, if
// ensure_ascii parameter is used, non-ASCII characters
if ((codepoint <= 0x1F) || (ensure_ascii && (codepoint >= 0x7F)))
{
if (codepoint <= 0xFFFF)
{
write_u_escape(bytes, static_cast<std::uint16_t>(codepoint));
}
else
{
write_u_escape(bytes, static_cast<std::uint16_t>(0xD7C0u + (codepoint >> 10u)));
write_u_escape(bytes, static_cast<std::uint16_t>(0xDC00u + (codepoint & 0x3FFu)));
}
}
else
{
// copy byte to buffer (all previous bytes
// been copied have in default case above)
string_buffer[bytes++] = s[i];
}
break;
}
}
// write buffer and reset index; there must be 13 bytes
// left, as this is the maximal number of bytes to be
// written ("\uxxxx\uxxxx\0") for one code point
if (string_buffer.size() - bytes < 13)
{
o->write_characters(string_buffer.data(), bytes);
bytes = 0;
}
// remember the byte position of this accept
bytes_after_last_accept = bytes;
undumped_chars = 0;
break;
}
case UTF8_REJECT: // decode found invalid UTF-8 byte
{
switch (error_handler)
{
case error_handler_t::strict:
{
JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", hex_bytes(byte | 0)), nullptr));
}
case error_handler_t::ignore:
case error_handler_t::replace:
{
// in case we saw this character the first time, we
// would like to read it again, because the byte
// may be OK for itself, but just not OK for the
// previous sequence
if (undumped_chars > 0)
{
--i;
}
// reset length buffer to the last accepted index;
// thus removing/ignoring the invalid characters
bytes = bytes_after_last_accept;
if (error_handler == error_handler_t::replace)
{
// add a replacement character
if (ensure_ascii)
{
string_buffer[bytes++] = '\\';
string_buffer[bytes++] = 'u';
string_buffer[bytes++] = 'f';
string_buffer[bytes++] = 'f';
string_buffer[bytes++] = 'f';
string_buffer[bytes++] = 'd';
}
else
{
string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xEF');
string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBF');
string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBD');
}
// write buffer and reset index; there must be 13 bytes
// left, as this is the maximal number of bytes to be
// written ("\uxxxx\uxxxx\0") for one code point
if (string_buffer.size() - bytes < 13)
{
o->write_characters(string_buffer.data(), bytes);
bytes = 0;
}
bytes_after_last_accept = bytes;
}
undumped_chars = 0;
// continue processing the string
state = UTF8_ACCEPT;
break;
}
default: // LCOV_EXCL_LINE
JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
}
break;
}
default: // decode found yet incomplete multibyte code point
{
if (!ensure_ascii)
{
// code point will not be escaped - copy byte to buffer
string_buffer[bytes++] = s[i];
}
++undumped_chars;
break;
}
}
}
// we finished processing the string
if (JSON_HEDLEY_LIKELY(state == UTF8_ACCEPT))
{
// write buffer
if (bytes > 0)
{
o->write_characters(string_buffer.data(), bytes);
}
}
else
{
// we finish reading, but do not accept: string was incomplete
switch (error_handler)
{
case error_handler_t::strict:
{
JSON_THROW(type_error::create(316, concat("incomplete UTF-8 string; last byte: 0x", hex_bytes(static_cast<std::uint8_t>(s[s.size() - 1] | 0))), nullptr));
}
case error_handler_t::ignore:
{
// write all accepted bytes
o->write_characters(string_buffer.data(), bytes_after_last_accept);
break;
}
case error_handler_t::replace:
{
// write all accepted bytes
o->write_characters(string_buffer.data(), bytes_after_last_accept);
// add a replacement character
if (ensure_ascii)
{
o->write_characters("\\ufffd", 6);
}
else
{
o->write_characters("\xEF\xBF\xBD", 3);
}
break;
}
default: // LCOV_EXCL_LINE
JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
}
}
}
private:
/*!
@brief count digits
Count the number of decimal (base 10) digits for an input unsigned integer.
@param[in] x unsigned integer number to count its digits
@return number of decimal digits
*/
unsigned int count_digits(number_unsigned_t x) noexcept
{
unsigned int n_digits = 1;
for (;;)
{
if (x < 10)
{
return n_digits;
}
if (x < 100)
{
return n_digits + 1;
}
if (x < 1000)
{
return n_digits + 2;
}
if (x < 10000)
{
return n_digits + 3;
}
x = x / 10000u;
n_digits += 4;
}
}
/*!
* @brief convert a byte to a uppercase hex representation
* @param[in] byte byte to represent
* @return representation ("00".."FF")
*/
static std::string hex_bytes(std::uint8_t byte)
{
std::string result = "FF";
constexpr const char* nibble_to_hex = "0123456789ABCDEF";
result[0] = nibble_to_hex[byte / 16];
result[1] = nibble_to_hex[byte % 16];
return result;
}
/*!
* @brief write a lowercase "\uXXXX" escape sequence into @a string_buffer
*
* Branch-free replacement for `snprintf(buf, 7, "\\u%04x", codeunit)` in the
* string escaping hot path. It writes exactly six characters ('\\', 'u' and
* four hex digits) at position @a pos of @a string_buffer via a nibble
* lookup table, avoiding the format-string parsing and locale machinery of
* `snprintf`. Advances @a pos by the number of bytes written (6).
*
* @param[in] pos position in @a string_buffer to write at; there must
* be at least 6 bytes of headroom
* @param[in] codeunit 16-bit value to encode
*/
void write_u_escape(std::size_t& pos, std::uint16_t codeunit) noexcept
{
JSON_ASSERT(string_buffer.size() - pos >= 6);
constexpr const char* nibble_to_hex = "0123456789abcdef";
string_buffer[pos + 0] = '\\';
string_buffer[pos + 1] = 'u';
string_buffer[pos + 2] = nibble_to_hex[(codeunit >> 12u) & 0x0Fu];
string_buffer[pos + 3] = nibble_to_hex[(codeunit >> 8u) & 0x0Fu];
string_buffer[pos + 4] = nibble_to_hex[(codeunit >> 4u) & 0x0Fu];
string_buffer[pos + 5] = nibble_to_hex[codeunit & 0x0Fu];
pos += 6;
}
/*!
@brief convert a single element of a binary value to its byte value
The elements of a binary value are dumped as the numbers 0..255, regardless
of the value type of the configured BinaryType: that type may be signed
(`char`), unsigned (`std::uint8_t`), or not an integer at all
(`std::byte`), none of which @ref dump_integer can handle uniformly.
*/
static std::uint8_t to_byte_value(binary_char_t x) noexcept
{
return static_cast<std::uint8_t>(x);
}
// templates to avoid warnings about useless casts
template <typename NumberType, enable_if_t<std::is_signed<NumberType>::value, int> = 0>
bool is_negative_number(NumberType x)
{
return x < 0;
}
template < typename NumberType, enable_if_t <std::is_unsigned<NumberType>::value, int > = 0 >
bool is_negative_number(NumberType /*unused*/)
{
return false;
}
/*!
@brief dump an integer
Dump a given integer to output stream @a o. Works internally with
@a number_buffer.
@param[in] x integer number (signed or unsigned) to dump
@tparam NumberType either @a number_integer_t or @a number_unsigned_t
*/
template < typename NumberType, detail::enable_if_t <
std::is_integral<NumberType>::value ||
std::is_same<NumberType, number_unsigned_t>::value ||
std::is_same<NumberType, number_integer_t>::value,
int > = 0 >
void dump_integer(NumberType x)
{
static constexpr std::array<std::array<char, 2>, 100> digits_to_99
{
{
{{'0', '0'}}, {{'0', '1'}}, {{'0', '2'}}, {{'0', '3'}}, {{'0', '4'}}, {{'0', '5'}}, {{'0', '6'}}, {{'0', '7'}}, {{'0', '8'}}, {{'0', '9'}},
{{'1', '0'}}, {{'1', '1'}}, {{'1', '2'}}, {{'1', '3'}}, {{'1', '4'}}, {{'1', '5'}}, {{'1', '6'}}, {{'1', '7'}}, {{'1', '8'}}, {{'1', '9'}},
{{'2', '0'}}, {{'2', '1'}}, {{'2', '2'}}, {{'2', '3'}}, {{'2', '4'}}, {{'2', '5'}}, {{'2', '6'}}, {{'2', '7'}}, {{'2', '8'}}, {{'2', '9'}},
{{'3', '0'}}, {{'3', '1'}}, {{'3', '2'}}, {{'3', '3'}}, {{'3', '4'}}, {{'3', '5'}}, {{'3', '6'}}, {{'3', '7'}}, {{'3', '8'}}, {{'3', '9'}},
{{'4', '0'}}, {{'4', '1'}}, {{'4', '2'}}, {{'4', '3'}}, {{'4', '4'}}, {{'4', '5'}}, {{'4', '6'}}, {{'4', '7'}}, {{'4', '8'}}, {{'4', '9'}},
{{'5', '0'}}, {{'5', '1'}}, {{'5', '2'}}, {{'5', '3'}}, {{'5', '4'}}, {{'5', '5'}}, {{'5', '6'}}, {{'5', '7'}}, {{'5', '8'}}, {{'5', '9'}},
{{'6', '0'}}, {{'6', '1'}}, {{'6', '2'}}, {{'6', '3'}}, {{'6', '4'}}, {{'6', '5'}}, {{'6', '6'}}, {{'6', '7'}}, {{'6', '8'}}, {{'6', '9'}},
{{'7', '0'}}, {{'7', '1'}}, {{'7', '2'}}, {{'7', '3'}}, {{'7', '4'}}, {{'7', '5'}}, {{'7', '6'}}, {{'7', '7'}}, {{'7', '8'}}, {{'7', '9'}},
{{'8', '0'}}, {{'8', '1'}}, {{'8', '2'}}, {{'8', '3'}}, {{'8', '4'}}, {{'8', '5'}}, {{'8', '6'}}, {{'8', '7'}}, {{'8', '8'}}, {{'8', '9'}},
{{'9', '0'}}, {{'9', '1'}}, {{'9', '2'}}, {{'9', '3'}}, {{'9', '4'}}, {{'9', '5'}}, {{'9', '6'}}, {{'9', '7'}}, {{'9', '8'}}, {{'9', '9'}},
}
};
// special case for "0"
if (x == 0)
{
o->write_character('0');
return;
}
// use a pointer to fill the buffer
auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
number_unsigned_t abs_value;
unsigned int n_chars{};
if (is_negative_number(x))
{
*buffer_ptr = '-';
abs_value = remove_sign(static_cast<number_integer_t>(x));
// account one more byte for the minus sign
n_chars = 1 + count_digits(abs_value);
}
else
{
abs_value = static_cast<number_unsigned_t>(x);
n_chars = count_digits(abs_value);
}
// spare 1 byte for '\0'
JSON_ASSERT(n_chars < number_buffer.size() - 1);
// jump to the end to generate the string from backward,
// so we later avoid reversing the result
buffer_ptr += static_cast<typename decltype(number_buffer)::difference_type>(n_chars);
// Fast int2ascii implementation inspired by "Fastware" talk by Andrei Alexandrescu
// See: https://www.youtube.com/watch?v=o4-CwDo2zpg
while (abs_value >= 100)
{
const auto digits_index = static_cast<unsigned>((abs_value % 100));
abs_value /= 100;
*(--buffer_ptr) = digits_to_99[digits_index][1];
*(--buffer_ptr) = digits_to_99[digits_index][0];
}
if (abs_value >= 10)
{
const auto digits_index = static_cast<unsigned>(abs_value);
*(--buffer_ptr) = digits_to_99[digits_index][1];
*(--buffer_ptr) = digits_to_99[digits_index][0];
}
else
{
*(--buffer_ptr) = static_cast<char>('0' + abs_value);
}
o->write_characters(number_buffer.data(), n_chars);
}
/*!
@brief dump a floating-point number
Dump a given floating-point number to output stream @a o. Works internally
with @a number_buffer.
@param[in] x floating-point number to dump
*/
void dump_float(number_float_t x)
{
// NaN / inf
if (!std::isfinite(x))
{
o->write_characters("null", 4);
return;
}
// If number_float_t is an IEEE-754 single or double precision number,
// use the Grisu2 algorithm to produce short numbers which are
// guaranteed to round-trip, using strtof and strtod, resp.
//
// NB: The test below works if <long double> == <double>.
static constexpr bool is_ieee_single_or_double
= (std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 24 && std::numeric_limits<number_float_t>::max_exponent == 128) ||
(std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 53 && std::numeric_limits<number_float_t>::max_exponent == 1024);
dump_float(x, std::integral_constant<bool, is_ieee_single_or_double>());
}
void dump_float(number_float_t x, std::true_type /*is_ieee_single_or_double*/)
{
auto* begin = number_buffer.data();
auto* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);
o->write_characters(begin, static_cast<size_t>(end - begin));
}
JSON_HEDLEY_NON_NULL(1)
static int snprintf_float(char* buf, std::size_t size, int d, double x)
{
// NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
return (std::snprintf)(buf, size, "%.*g", d, x);
}
JSON_HEDLEY_NON_NULL(1)
static int snprintf_float(char* buf, std::size_t size, int d, long double x)
{
// NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
return (std::snprintf)(buf, size, "%.*Lg", d, x);
}
void dump_float(number_float_t x, std::false_type /*is_ieee_single_or_double*/)
{
// get the number of digits for a float -> text -> float round-trip
static constexpr auto d = std::numeric_limits<number_float_t>::max_digits10;
// the actual conversion
std::ptrdiff_t len = snprintf_float(number_buffer.data(), number_buffer.size(), d, x);
// negative value indicates an error
JSON_ASSERT(len > 0);
// check if the buffer was large enough
JSON_ASSERT(static_cast<std::size_t>(len) < number_buffer.size());
// erase thousands separators
if (thousands_sep != '\0')
{
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::remove returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto end = std::remove(number_buffer.begin(), number_buffer.begin() + len, thousands_sep);
std::fill(end, number_buffer.end(), '\0');
JSON_ASSERT((end - number_buffer.begin()) <= len);
len = (end - number_buffer.begin());
}
// convert decimal point to '.'
if (decimal_point != '\0' && decimal_point != '.')
{
// NOLINTNEXTLINE(readability-qualified-auto,llvm-qualified-auto): std::find returns an iterator, see https://github.com/nlohmann/json/issues/3081
const auto dec_pos = std::find(number_buffer.begin(), number_buffer.end(), decimal_point);
if (dec_pos != number_buffer.end())
{
*dec_pos = '.';
}
}
o->write_characters(number_buffer.data(), static_cast<std::size_t>(len));
// determine if we need to append ".0"
const bool value_is_int_like =
std::none_of(number_buffer.begin(), number_buffer.begin() + len + 1,
[](char c)
{
return c == '.' || c == 'e';
});
if (value_is_int_like)
{
o->write_characters(".0", 2);
}
}
/*!
@brief check whether a string is UTF-8 encoded
The function checks each byte of a string whether it is UTF-8 encoded. The
result of the check is stored in the @a state parameter. The function must
be called initially with state 0 (accept). State 1 means the string must
be rejected, because the current byte is not allowed. If the string is
completely processed, but the state is non-zero, the string ended
prematurely; that is, the last byte indicated more bytes should have
followed.
@param[in,out] state the state of the decoding
@param[in,out] codep codepoint (valid only if resulting state is UTF8_ACCEPT)
@param[in] byte next byte to decode
@return new state
@note The function has been edited: a std::array is used.
@copyright Copyright (c) 2008-2009 Bjoern Hoehrmann <bjoern@hoehrmann.de>
@sa http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
*/
static std::uint8_t decode(std::uint8_t& state, std::uint32_t& codep, const std::uint8_t byte) noexcept
{
static const std::array<std::uint8_t, 400> utf8d =
{
{
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 00..1F
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 20..3F
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 40..5F
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 60..7F
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, // 80..9F
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, // A0..BF
8, 8, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // C0..DF
0xA, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x3, 0x4, 0x3, 0x3, // E0..EF
0xB, 0x6, 0x6, 0x6, 0x5, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, 0x8, // F0..FF
0x0, 0x1, 0x2, 0x3, 0x5, 0x8, 0x7, 0x1, 0x1, 0x1, 0x4, 0x6, 0x1, 0x1, 0x1, 0x1, // s0..s0
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, // s1..s2
1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, // s3..s4
1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 3, 1, 1, 1, 1, 1, 1, // s5..s6
1, 3, 1, 1, 1, 1, 1, 3, 1, 3, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 // s7..s8
}
};
JSON_ASSERT(static_cast<std::size_t>(byte) < utf8d.size());
const std::uint8_t type = utf8d[byte];
codep = (state != UTF8_ACCEPT)
? (byte & 0x3fu) | (codep << 6u)
: (0xFFu >> type) & (byte);
const std::size_t index = 256u + (static_cast<size_t>(state) * 16u) + static_cast<size_t>(type);
JSON_ASSERT(index < utf8d.size());
state = utf8d[index];
return state;
}
/*
* Overload to make the compiler happy while it is instantiating
* dump_integer for number_unsigned_t.
* Must never be called.
*/
number_unsigned_t remove_sign(number_unsigned_t x)
{
JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
return x; // LCOV_EXCL_LINE
}
/*
* Helper function for dump_integer
*
* This function takes a negative signed integer and returns its absolute
* value as an unsigned integer. The plus/minus shuffling is necessary as we
* cannot directly remove the sign of an arbitrary signed integer as the
* absolute values of INT_MIN and INT_MAX are usually not the same. See
* #1708 for details.
*/
number_unsigned_t remove_sign(number_integer_t x) noexcept
{
JSON_ASSERT(x < 0 && x < (std::numeric_limits<number_integer_t>::max)()); // NOLINT(misc-redundant-expression)
return static_cast<number_unsigned_t>(-(x + 1)) + 1;
}
private:
/// the output of the serializer
output_adapter_t<char> o = nullptr;
/// a (hopefully) large enough character buffer
std::array<char, 64> number_buffer{{}};
/// the locale
const std::lconv* loc = nullptr;
/// the locale's thousand separator character
const char thousands_sep = '\0';
/// the locale's decimal point character
const char decimal_point = '\0';
/// string buffer
std::array<char, 512> string_buffer{{}};
/// the indentation character
const char indent_char;
/// the indentation string
string_t indent_string;
/// error_handler how to react on decoding errors
const error_handler_t error_handler;
};
} // namespace detail
NLOHMANN_JSON_NAMESPACE_END
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