102 lines
2.8 KiB
Markdown
102 lines
2.8 KiB
Markdown
# nlohmann::basic_json::parse_event_t
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```
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enum class parse_event_t : std::uint8_t {
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object_start,
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object_end,
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array_start,
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array_end,
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key,
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value
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};
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```
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The parser callback distinguishes the following events:
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- `object_start`: the parser read `{` and started to process a JSON object
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- `key`: the parser read a key of a value in an object
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- `object_end`: the parser read `}` and finished processing a JSON object
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- `array_start`: the parser read `[` and started to process a JSON array
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- `array_end`: the parser read `]` and finished processing a JSON array
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- `value`: the parser finished reading a JSON value
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## Examples
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Each coloured dot marks where the parser reports a `parse_event_t` event while reading the JSON text on the left; the legend on the right names the event per colour.
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Example
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The following code parses a small JSON text with a parser callback that reports every event together with its depth and keeps every value (by always returning `true`).
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```
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#include <iostream>
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#include <string>
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#include <nlohmann/json.hpp>
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using nlohmann::json;
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// translate a parse_event_t to a human-readable name
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std::string event_name(json::parse_event_t event)
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{
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switch (event)
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{
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case json::parse_event_t::object_start:
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return "object_start";
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case json::parse_event_t::object_end:
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return "object_end";
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case json::parse_event_t::array_start:
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return "array_start";
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case json::parse_event_t::array_end:
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return "array_end";
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case json::parse_event_t::key:
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return "key";
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case json::parse_event_t::value:
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return "value";
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default:
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return "unknown";
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}
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}
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int main()
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{
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// a small JSON text
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const auto* text = R"({"pi": 3.141, "numbers": [1, 2]})";
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// parse the text and report every event together with its depth;
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// returning true keeps every value unchanged
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json j = json::parse(text, [](int depth, json::parse_event_t event, json& /*parsed*/)
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{
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std::cout << depth << " " << event_name(event) << '\n';
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return true;
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});
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// the callback did not change anything, so the parsed value is unaffected
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std::cout << j << '\n';
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}
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```
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Output:
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```
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0 object_start
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1 key
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1 value
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1 key
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1 array_start
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2 value
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2 value
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1 array_end
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0 object_end
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{"numbers":[1,2],"pi":3.141}
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```
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## See also
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- [`parser_callback_t`](https://json.nlohmann.me/api/basic_json/parser_callback_t/index.md) - callback function type for the parser
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- [`parse`](https://json.nlohmann.me/api/basic_json/parse/index.md) - deserialize from a compatible input
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- [Parser Callbacks](https://json.nlohmann.me/features/parsing/parser_callbacks/index.md) - filter or inspect values while parsing
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## Version history
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- Added in version 1.0.0.
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