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nlohmann
132 lines
3.6 KiB
Markdown
132 lines
3.6 KiB
Markdown
# nlohmann::operator\<<(basic_json), nlohmann::operator\<<(json_pointer)
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```
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std::ostream& operator<<(std::ostream& o, const basic_json& j); // (1)
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std::ostream& operator<<(std::ostream& o, const json_pointer& ptr); // (2)
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```
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1. Serialize the given JSON value `j` to the output stream `o`. The JSON value will be serialized using the [`dump`](https://json.nlohmann.me/api/basic_json/dump/index.md) member function.
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- The indentation of the output can be controlled with the member variable `width` of the output stream `o`. For instance, using the manipulator `std::setw(4)` on `o` sets the indentation level to `4` and the serialization result is the same as calling `dump(4)`.
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- The indentation character can be controlled with the member variable `fill` of the output stream `o`. For instance, the manipulator `std::setfill('\\t')` sets indentation to use a tab character rather than the default space character.
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1. Write a string representation of the given JSON pointer `ptr` to the output stream `o`. The string representation is obtained using the [`to_string`](https://json.nlohmann.me/api/json_pointer/to_string/index.md) member function.
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## Parameters
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`o` (in, out) : stream to write to
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`j` (in) : JSON value to serialize
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`ptr` (in) : JSON pointer to write
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## Return value
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the stream `o`
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## Exceptions
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1. Throws [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316) if a string stored inside the JSON value is not UTF-8 encoded. Note that unlike the [`dump`](https://json.nlohmann.me/api/basic_json/dump/index.md) member functions, no `error_handler` can be set.
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1. None.
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## Complexity
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Linear.
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## Notes
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Deprecation
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Function `std::ostream& operator<<(std::ostream& o, const basic_json& j)` replaces function `std::ostream& operator>>(const basic_json& j, std::ostream& o)` which has been deprecated in version 3.0.0. It will be removed in version 4.0.0. Please replace calls like `j >> o;` with `o << j;`.
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## Examples
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Example: (1) serialize JSON value to stream
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The example below shows the serialization with different parameters to `width` to adjust the indentation level.
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```
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#include <iostream>
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#include <iomanip>
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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 JSON values
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json j_object = {{"one", 1}, {"two", 2}};
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json j_array = {1, 2, 4, 8, 16};
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// serialize without indentation
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std::cout << j_object << "\n\n";
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std::cout << j_array << "\n\n";
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// serialize with indentation
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std::cout << std::setw(4) << j_object << "\n\n";
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std::cout << std::setw(2) << j_array << "\n\n";
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std::cout << std::setw(1) << std::setfill('\t') << j_object << "\n\n";
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}
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```
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Output:
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```
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{"one":1,"two":2}
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[1,2,4,8,16]
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{
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"one": 1,
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"two": 2
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}
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[
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1,
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2,
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4,
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8,
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16
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]
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{
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"one": 1,
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"two": 2
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}
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```
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Example: (2) write JSON pointer to stream
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The example below shows how to write a JSON pointer to a stream.
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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 JSON pointer
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json::json_pointer ptr("/foo/bar/baz");
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// write string representation to stream
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std::cout << ptr << std::endl;
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}
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```
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Output:
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```
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/foo/bar/baz
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```
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## See also
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- [dump](https://json.nlohmann.me/api/basic_json/dump/index.md) - serialize to a JSON-formatted string
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- [Serialization](https://json.nlohmann.me/features/serialization/index.md) - the serialization article
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## Version history
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1. Added in version 1.0.0. Added support for indentation character and deprecated `std::ostream& operator>>(const basic_json& j, std::ostream& o)` in version 3.0.0.
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1. Added in version 3.11.0.
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