265 lines
9.5 KiB
Markdown
265 lines
9.5 KiB
Markdown
# nlohmann::basic_json::swap
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```
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// (1)
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void swap(reference other) noexcept (
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std::is_nothrow_move_constructible<value_t>::value &&
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std::is_nothrow_move_assignable<value_t>::value &&
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std::is_nothrow_move_constructible<json_value>::value &&
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std::is_nothrow_move_assignable<json_value>::value &&
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std::is_nothrow_move_constructible<json_base_class_t>::value &&
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std::is_nothrow_move_assignable<json_base_class_t>::value
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);
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// (2)
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friend void swap(reference left, reference right) noexcept (
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std::is_nothrow_move_constructible<value_t>::value &&
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std::is_nothrow_move_assignable<value_t>::value &&
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std::is_nothrow_move_constructible<json_value>::value &&
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std::is_nothrow_move_assignable<json_value>::value &&
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std::is_nothrow_move_constructible<json_base_class_t>::value &&
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std::is_nothrow_move_assignable<json_base_class_t>::value
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);
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// (3)
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void swap(array_t& other);
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// (4)
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void swap(object_t& other);
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// (5)
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void swap(string_t& other);
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// (6)
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void swap(binary_t& other);
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// (7)
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void swap(typename binary_t::container_type& other);
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```
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1. Exchanges the contents of the JSON value with those of `other`. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. If macro [`JSON_DIAGNOSTIC_POSITIONS`](https://json.nlohmann.me/api/macros/json_diagnostic_positions/index.md) is defined to `1`, the [`start_pos()`](https://json.nlohmann.me/api/basic_json/start_pos/index.md)/[`end_pos()`](https://json.nlohmann.me/api/basic_json/end_pos/index.md) diagnostic positions are exchanged along with the value. The [`json_base_class_t`](https://json.nlohmann.me/api/basic_json/json_base_class_t/index.md) subobject is exchanged along with the value as well, the same way it is copied or moved by the copy/move constructors and assignment operators.
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1. Exchanges the contents of the JSON value from `left` with those of `right`. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. Implemented as a friend function callable via ADL. If macro [`JSON_DIAGNOSTIC_POSITIONS`](https://json.nlohmann.me/api/macros/json_diagnostic_positions/index.md) is defined to `1`, the [`start_pos()`](https://json.nlohmann.me/api/basic_json/start_pos/index.md)/[`end_pos()`](https://json.nlohmann.me/api/basic_json/end_pos/index.md) diagnostic positions are exchanged along with the value. The [`json_base_class_t`](https://json.nlohmann.me/api/basic_json/json_base_class_t/index.md) subobject is exchanged along with the value as well, the same way it is copied or moved by the copy/move constructors and assignment operators.
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1. Exchanges the contents of a JSON array with those of `other`. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
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1. Exchanges the contents of a JSON object with those of `other`. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
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1. Exchanges the contents of a JSON string with those of `other`. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
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1. Exchanges the contents of a binary value with those of `other`. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
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1. Exchanges the contents of a binary value with those of `other`. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated. Unlike version (6), no binary subtype is involved.
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## Parameters
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`other` (in, out) : value to exchange the contents with
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`left` (in, out) : value to exchange the contents with
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`right` (in, out) : value to exchange the contents with
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## Exception safety
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1. No-throw guarantee: this function never throws exceptions.
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1. No-throw guarantee: this function never throws exceptions.
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1. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
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1. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
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1. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
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1. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
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1. Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
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## Exceptions
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1. No-throw guarantee: this function never throws exceptions.
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1. No-throw guarantee: this function never throws exceptions.
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1. Throws [`type_error.310`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error310) if called on JSON values other than arrays; example: `"cannot use swap(array_t&) with boolean"`
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1. Throws [`type_error.310`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error310) if called on JSON values other than objects; example: `"cannot use swap(object_t&) with boolean"`
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1. Throws [`type_error.310`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error310) if called on JSON values other than strings; example: `"cannot use swap(string_t&) with boolean"`
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1. Throws [`type_error.310`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error310) if called on JSON values other than binaries; example: `"cannot use swap(binary_t&) with boolean"`
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1. Throws [`type_error.310`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error310) if called on JSON values other than binaries; example: `"cannot use swap(binary_t::container_type&) with boolean"`
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## Complexity
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Constant.
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## Examples
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Example: (1, 2) swap JSON values
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The example below shows how JSON values can be swapped with `swap()`.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create two JSON values
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json j1 = {1, 2, 3, 4, 5};
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json j2 = {{"pi", 3.141592653589793}, {"e", 2.718281828459045}};
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// swap the values
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j1.swap(j2);
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// output the values
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std::cout << "j1 = " << j1 << '\n';
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std::cout << "j2 = " << j2 << '\n';
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}
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```
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Output:
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```
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j1 = {"e":2.718281828459045,"pi":3.141592653589793}
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j2 = [1,2,3,4,5]
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```
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Example: (3) swap array
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The example below shows how arrays can be swapped with `swap()`.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create a JSON value
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json value = {{"array", {1, 2, 3, 4}}};
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// create an array_t
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json::array_t array = {"Snap", "Crackle", "Pop"};
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// swap the array stored in the JSON value
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value["array"].swap(array);
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// output the values
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std::cout << "value = " << value << '\n';
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std::cout << "array = " << array << '\n';
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}
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```
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Output:
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```
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value = {"array":["Snap","Crackle","Pop"]}
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array = [1,2,3,4]
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```
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Example: (4) swap object
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The example below shows how objects can be swapped with `swap()`.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create a JSON value
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json value = { {"translation", {{"one", "eins"}, {"two", "zwei"}}} };
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// create an object_t
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json::object_t object = {{"cow", "Kuh"}, {"dog", "Hund"}};
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// swap the object stored in the JSON value
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value["translation"].swap(object);
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// output the values
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std::cout << "value = " << value << '\n';
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std::cout << "object = " << object << '\n';
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}
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```
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Output:
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```
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value = {"translation":{"cow":"Kuh","dog":"Hund"}}
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object = {"one":"eins","two":"zwei"}
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```
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Example: (5) swap string
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The example below shows how strings can be swapped with `swap()`.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create a JSON value
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json value = { "the good", "the bad", "the ugly" };
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// create string_t
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json::string_t string = "the fast";
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// swap the object stored in the JSON value
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value[1].swap(string);
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// output the values
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std::cout << "value = " << value << '\n';
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std::cout << "string = " << string << '\n';
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}
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```
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Output:
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```
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value = ["the good","the fast","the ugly"]
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string = the bad
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```
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Example: (6) swap binary
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The example below shows how binary values can be swapped with `swap()`.
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```
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create a binary value
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json value = json::binary({1, 2, 3});
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// create a binary_t
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json::binary_t binary = {{4, 5, 6}};
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// swap the object stored in the JSON value
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value.swap(binary);
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// output the values
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std::cout << "value = " << value << '\n';
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std::cout << "binary = " << json(binary) << '\n';
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}
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```
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Output:
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```
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value = {"bytes":[4,5,6],"subtype":null}
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binary = {"bytes":[1,2,3],"subtype":null}
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```
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## See also
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- [std::swap\<basic_json>](https://json.nlohmann.me/api/basic_json/std_swap/index.md)
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- [operator=](https://json.nlohmann.me/api/basic_json/operator%3D/index.md) copy assignment
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- [basic_json](https://json.nlohmann.me/api/basic_json/basic_json/index.md) create a JSON value
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## Version history
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1. Added in version 1.0.0. Exchanges the `json_base_class_t` subobject along with the value since version 3.13.0 unreleased.
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1. Added in version 1.0.0. Exchanges the `json_base_class_t` subobject along with the value since version 3.13.0 unreleased.
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1. Added in version 1.0.0.
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1. Added in version 1.0.0.
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1. Added in version 1.0.0.
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1. Added in version 3.8.0.
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1. Added in version 3.8.0.
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