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nlohmannjson/doc/examples/sax_parse.cpp

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#include <iostream>
#include <iomanip>
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
// a simple event consumer that collects string representations of the passed
// values; not inheriting from json::json_sax_t is not required, but can
// help not to forget a required function
class sax_event_consumer : public json::json_sax_t
{
public:
std::vector<std::string> events;
bool null() override
{
events.push_back("value: null");
return true;
}
bool boolean(bool val) override
{
events.push_back("value: " + std::string(val ? "true" : "false"));
return true;
}
bool number_integer(number_integer_t val) override
{
events.push_back("value: " + std::to_string(val));
return true;
}
bool number_unsigned(number_unsigned_t val) override
{
events.push_back("value: " + std::to_string(val));
return true;
}
bool number_float(number_float_t val, const string_t& s) override
{
events.push_back("value: " + s);
return true;
}
bool string(string_t& val) override
{
events.push_back("value: " + val);
return true;
}
bool start_object(std::size_t elements) override
{
events.push_back("start: object");
return true;
}
bool end_object() override
{
events.push_back("end: object");
return true;
}
bool start_array(std::size_t elements) override
{
events.push_back("start: array");
return true;
}
bool end_array() override
{
events.push_back("end: array");
return true;
}
bool key(string_t& val) override
{
events.push_back("key: " + val);
return true;
}
bool binary(json::binary_t& val) override
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{
events.push_back("binary");
return true;
}
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bool parse_error(std::size_t position, const std::string& last_token, const json::exception& ex) override
{
events.push_back("error: " + std::string(ex.what()));
return false;
}
};
int main()
{
// a JSON text
auto text = R"(
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": 100
},
"Animated" : false,
"IDs": [116, 943, 234, 38793],
"Distance": 12.723374634
}
}
)";
// create a SAX event consumer object
sax_event_consumer sec;
// parse and serialize JSON
bool result = json::sax_parse(text, &sec);
// output the recorded events
for (auto& event : sec.events)
{
std::cout << "(" << event << ") ";
}
// output the result of sax_parse
std::cout << "\nresult: " << std::boolalpha << result << std::endl;
}