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nlohmann::json_sax::parse_error

virtual bool parse_error(std::size_t position,
                         const std::string& last_token,
                         const detail::exception& ex) = 0;

A parse error occurred.

Parameters

position (in)
the position in the input where the error occurs
last_token (in)
the last read token
ex (in)
an exception object describing the error

Return value

Whether parsing should proceed (must return false).

Examples

Example

The example below shows how the SAX interface is used.

#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; note 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("null()");
        return true;
    }

    bool boolean(bool val) override
    {
        events.push_back("boolean(val=" + std::string(val ? "true" : "false") + ")");
        return true;
    }

    bool number_integer(number_integer_t val) override
    {
        events.push_back("number_integer(val=" + std::to_string(val) + ")");
        return true;
    }

    bool number_unsigned(number_unsigned_t val) override
    {
        events.push_back("number_unsigned(val=" + std::to_string(val) + ")");
        return true;
    }

    bool number_float(number_float_t val, const string_t& s) override
    {
        events.push_back("number_float(val=" + std::to_string(val) + ", s=" + s + ")");
        return true;
    }

    bool string(string_t& val) override
    {
        events.push_back("string(val=" + val + ")");
        return true;
    }

    bool start_object(std::size_t elements) override
    {
        events.push_back("start_object(elements=" + std::to_string(elements) + ")");
        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(elements=" + std::to_string(elements) + ")");
        return true;
    }

    bool end_array() override
    {
        events.push_back("end_array()");
        return true;
    }

    bool key(string_t& val) override
    {
        events.push_back("key(val=" + val + ")");
        return true;
    }

    bool binary(json::binary_t& val) override
    {
        events.push_back("binary(val=[...])");
        return true;
    }

    bool parse_error(std::size_t position, const std::string& last_token, const json::exception& ex) override
    {
        events.push_back("parse_error(position=" + std::to_string(position) + ", last_token=" + last_token + ",\n            ex=" + 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],
            "DeletionDate": null,
            "Distance": 12.723374634
        }
    }]
    )";

    // create a SAX event consumer object
    sax_event_consumer sec;

    // parse JSON
    bool result = json::sax_parse(text, &sec);

    // output the recorded events
    for (auto& event : sec.events)
    {
        std::cout << event << "\n";
    }

    // output the result of sax_parse
    std::cout << "\nresult: " << std::boolalpha << result << std::endl;
}

Output:

start_object(elements=18446744073709551615)
key(val=Image)
start_object(elements=18446744073709551615)
key(val=Width)
number_unsigned(val=800)
key(val=Height)
number_unsigned(val=600)
key(val=Title)
string(val=View from 15th Floor)
key(val=Thumbnail)
start_object(elements=18446744073709551615)
key(val=Url)
string(val=http://www.example.com/image/481989943)
key(val=Height)
number_unsigned(val=125)
key(val=Width)
number_unsigned(val=100)
end_object()
key(val=Animated)
boolean(val=false)
key(val=IDs)
start_array(elements=18446744073709551615)
number_unsigned(val=116)
number_unsigned(val=943)
number_unsigned(val=234)
number_integer(val=-38793)
end_array()
key(val=DeletionDate)
null()
key(val=Distance)
number_float(val=12.723375, s=12.723374634)
end_object()
end_object()
parse_error(position=460, last_token=12.723374634<U+000A>        }<U+000A>    }],
            ex=[json.exception.parse_error.101] parse error at line 17, column 6: syntax error while parsing value - unexpected ']'; expected end of input)

result: false

Version history

  • Added in version 3.2.0.

Last update: September 18, 2022