Parse error

[xabik]

When I execute this function, I get an exception like
nlohmann :: detail :: parse_error

	void load_info(std::vector<json> info) {
		std::ifstream f;
		f.open("info.json", std::ifstream::in);
		json building;
		while (f >> building) {
			info.push_back(building);
		}
		f.close();
	}

file info.json with info like this

{"coordinates":{"lt":{"x":52,"y":121},"rb":{"x":140,"y":43}},"order":1,"type":19}
{"coordinates":{"lt":{"x":55,"y":118},"rb":{"x":137,"y":46}},"order":3,"type":19}
{"coordinates":{"lt":{"x":54,"y":120},"rb":{"x":135,"y":43}},"order":2,"type":21}
{"coordinates":{"lt":{"x":54,"y":123},"rb":{"x":135,"y":40}},"order":4,"type":21}

but if i change my function to:

	void load_info(std::vector<json> info) {
		std::ifstream f;
		f.open("info.json", std::ifstream::in);
		json building;
		for (int i = 0; i < 4; i++) {
			f >> building;
			info.push_back(building);
		}
		f.close();
	}

function work good. How i can fix this?

MS Visual Studio 2017. Windows 7.

Version library 3.7.0 Release

[nlohmann]

What is the exact exception description?

[xabik]

Message with exception have only address in memory. Debugger stop program in case 4: in

    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
                     const detail::exception& ex)
    {
        errored = true;
        if (allow_exceptions)
        {
            // determine the proper exception type from the id
            switch ((ex.id / 100) % 100)
            {
                case 1:
                    JSON_THROW(*static_cast<const detail::parse_error*>(&ex));
                case 4:
                    JSON_THROW(*static_cast<const detail::out_of_range*>(&ex));
                // LCOV_EXCL_START
                case 2:
                    JSON_THROW(*static_cast<const detail::invalid_iterator*>(&ex));
                case 3:
                    JSON_THROW(*static_cast<const detail::type_error*>(&ex));
                case 5:
                    JSON_THROW(*static_cast<const detail::other_error*>(&ex));
                default:
                    assert(false);
                    // LCOV_EXCL_STOP
            }
        }
        return false;
    }

[nlohmann]

You should still be able to access the what() member of the exception. As it seems to be an json::exception::out_of_range which only occurs in https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/input/parser.hpp#L265, your input seems to contain number that overflow. This is strange.

• Can you narrow down the error to a smaller input that you can share?
• Can you try to access the exception's what() message as it should give you the token where the error happend?

[xabik]

For more detail, I wrote a simple program. It first writes the information to a file, and then reads it. An error occurs at the reading stage.

#include "pch.h"
#include <iostream>
#include <nlohmann/json.hpp>
#include <fstream>

using json = nlohmann::json;

void write_to_file(json info) {
	std::ofstream f;
	f.open("info.json", std::ofstream::app);
	f << info << std::endl;
	f.close();
}

void read_from_file(std::vector<json> info) {
	std::ifstream f;
	f.open("info.json", std::ifstream::in);
	json building;
	while (f >> building) {
		info.push_back(building);
	}
	f.close();
}

int main()
{
	json test1 = {
	  {"type", 19},
	  {"coordinates", {
		{"lt", {
		  {"x", 52},
		  {"y", 121}
		}},
		{"rb", {
		  {"x", 140},
		  {"y", 43}
		}}
	  }},
	  {"order", 1}
	};

	json test2 = {
	  {"type", 21},
	  {"coordinates", {
		{"lt", {
		  {"x", 55},
		  {"y", 118}
		}},
		{"rb", {
		  {"x", 137},
		  {"y", 46}
		}}
	  }},
	  {"order", 3}
	};
	write_to_file(test1);
	write_to_file(test2);
	std::vector<json> info;
	read_from_file(info);
}

The what() member of the exception = {_What=0x009e0240 "[json.exception.parse_error.101] parse error at line 2, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal" ...} | __std_exception_data

In https://nlohmann.github.io/json/classnlohmann_1_1basic__json_af1efc2468e6022be6e35fc2944cabe4d.html Error 101 describes is an invalid format. But the file is written using the library functions. Perhaps I am writing incorrectly?

[xabik]

[nlohmann]

I can reproduce the exception. I'll try to dig deeper later this week.

[DJLink]

I'm running into a similar exception as @xabik mentioned. Weirdly if I have my json in "beautified" mode when loading it parses correctly, using any online tool to minify (or writing it by hand) and the same exact json hits that exception.

So I decided to break that minified json into a 2 line and now it loads.
1 line minified json gives exceptions, >1 loads ok.
Hope this helps.

[xabik]

@DJLink, can you attach file with json which loads correctly? I try to repeat loading.

[DJLink]

Here are 3 files, the single line file fails, the other load ok.

I'm using nlohmann::json::parse()

test_ok_2_lines.txt
test_ok_beautify.txt
test_fail.txt

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[nlohmann]

I had another look at #1761 (comment). The issue is that operator>> does not return false in case of a parse error. Hence, for an input like

{"coordinates":{"lt":{"x":52,"y":121},"rb":{"x":140,"y":43}},"order":1,"type":19}
{"coordinates":{"lt":{"x":55,"y":118},"rb":{"x":137,"y":46}},"order":3,"type":21}

operator>> only returns successfully twice - calling it a third time yields a parse error exception.

Hence, you would need code like

    try {
        while (f >> building) {
            info.push_back(building);
        }
    } catch (json::exception&)
    {}

to parse an arbitrary number of JSON values in a file.

[nlohmann]

Do you need further assistance with this issue?