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nlohmann
174 lines
4.7 KiB
Markdown
174 lines
4.7 KiB
Markdown
# nlohmann::basic_json::dump
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```
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string_t dump(const int indent = -1,
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const char indent_char = ' ',
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const bool ensure_ascii = false,
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const error_handler_t error_handler = error_handler_t::strict) const;
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```
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Serialization function for JSON values. The function tries to mimic Python's [`json.dumps()` function](https://docs.python.org/2/library/json.html#json.dump), and currently supports its `indent` and `ensure_ascii` parameters.
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## Parameters
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`indent` (in) : If `indent` is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of `0` will only insert newlines. `-1` (the default) selects the most compact representation.
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`indent_char` (in) : The character to use for indentation if `indent` is greater than `0`. The default is (space).
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`ensure_ascii` (in) : If `ensure_ascii` is true, all non-ASCII characters in the output are escaped with `\uXXXX` sequences, and the result consists of ASCII characters only.
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`error_handler` (in) : how to react on decoding errors; there are three possible values (see [`error_handler_t`](https://json.nlohmann.me/api/basic_json/error_handler_t/index.md): `strict` (throws an exception in case a decoding error occurs; default), `replace` (replace invalid UTF-8 sequences with U+FFFD), and `ignore` (ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the output unchanged, and invalid bytes are dropped)).
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## Return value
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string containing the serialization of the JSON value
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## Exception safety
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Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
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## Exceptions
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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 and `error_handler` is set to `strict`
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## Complexity
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Linear.
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## Notes
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Binary values are serialized as an object containing two keys:
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- "bytes": an array of bytes as integers
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- "subtype": the subtype as integer or `null` if the binary has no subtype
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## Examples
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Example
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The following example shows the effect of different `indent`, `indent_char`, and `ensure_ascii` parameters to the result of the serialization.
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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 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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json j_string = "Hellö 😀!";
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// call dump()
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std::cout << "objects:" << '\n'
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<< j_object.dump() << "\n\n"
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<< j_object.dump(-1) << "\n\n"
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<< j_object.dump(0) << "\n\n"
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<< j_object.dump(4) << "\n\n"
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<< j_object.dump(1, '\t') << "\n\n";
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std::cout << "arrays:" << '\n'
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<< j_array.dump() << "\n\n"
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<< j_array.dump(-1) << "\n\n"
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<< j_array.dump(0) << "\n\n"
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<< j_array.dump(4) << "\n\n"
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<< j_array.dump(1, '\t') << "\n\n";
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std::cout << "strings:" << '\n'
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<< j_string.dump() << '\n'
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<< j_string.dump(-1, ' ', true) << '\n';
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// create JSON value with invalid UTF-8 byte sequence
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json j_invalid = "ä\xA9ü";
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try
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{
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std::cout << j_invalid.dump() << std::endl;
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}
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catch (const json::type_error& e)
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{
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std::cout << e.what() << std::endl;
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}
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std::cout << "string with replaced invalid characters: "
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<< j_invalid.dump(-1, ' ', false, json::error_handler_t::replace)
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<< "\nstring with ignored invalid characters: "
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<< j_invalid.dump(-1, ' ', false, json::error_handler_t::ignore)
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<< '\n';
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}
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```
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Output:
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```
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objects:
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{"one":1,"two":2}
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{"one":1,"two":2}
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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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"one": 1,
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"two": 2
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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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arrays:
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[1,2,4,8,16]
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[1,2,4,8,16]
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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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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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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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strings:
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"Hellö 😀!"
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"Hell\u00f6 \ud83d\ude00!"
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[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9
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string with replaced invalid characters: "ä�ü"
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string with ignored invalid characters: "äü"
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```
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## See also
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- [to_string](https://json.nlohmann.me/api/basic_json/to_string/index.md) returns a string representation of a JSON value
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- [operator\<<](https://json.nlohmann.me/api/operator_ltlt/index.md) serialize to stream
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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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- Added in version 1.0.0.
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- Indentation character `indent_char`, option `ensure_ascii` and exceptions added in version 3.0.0.
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- Error handlers added in version 3.4.0.
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- Serialization of binary values added in version 3.8.0.
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