Error: out_of_range

[david9472]

I'm trying to read in a .txt file which is packed with JSON Objects. Afterwards I want to get a specific object out of the document, but everytime I try to run my problem I get an Error-Message like:

untreated exception at 0x778B17D2 in "programm_name.exe": Microsoft C++-exception:nlohmann:detail:parse_error at memorylocation 0x008FE65C

(Sorry for bad english);
However this is just for testing purpose. Later I want to parse the return string of an function.
But for this problem my code looks like this:

`string text;
json temp;

ifstream read;
read.open("response_enumerate.txt");
getline(read, text);
read.close();
json in = json::parse(text);

temp = in["/device/command/0"_json_pointer];
cout << temp;`

and my .txt file with the JSON Objects looks like this (just a part of it because otherwise nobody would look at this post because it would be to long)

{"device":[{ "command":"enumerate", "statusCode":0, "wait":0, "deviceMake":"Digilent", "deviceModel":"OpenScope MZ", "firmwareVersion":{ "major":1, "minor":301, "patch":0}, "macAddress":"00:7E:G0:8B:6C:CC", "calibrationSource":"flash", "nics":{ "wlan0":{ "macAddress":"00:1E:B0:8B:5B:AC"}}, "requiredCalibrationVer":17, "requiredWiFiParameterVer":8, "awg":{ "numChans":1,

[nlohmann]

The problem seems to be that your input is invalid JSON. At least this is the output you mention. I am confused, because the title of this issue mentions out_of_range. Are these two individual problems?

The parse error should also contain a position in the code (since 3.4.0 with a line and column), and a detailed error message (like "unexepected end of file" or "invalid Unicode byte"). Can you please double check whether you can get the complete error message? You could also catch json::parse_error and output the result of .what().

Furthermore, you could use tools like https://jsonlint.com to see where the parse error is.

[david9472]

No I think that these problems are linked together. It's not like an "classic" error which appears in the Error-Section. While debugging it just stops the process, opens the "json_sax.hpp" file, and indicates an error in line 253 which says:

case 4: JSON_THROW(reinterpret_cast<const detail::out_of_range>(&ex)) // LCOV_EXCL_START

Thats why I mentioned "out_of_range" in the title of this issue.

And it says, as I mentioned above:

untreated exception at 0x778B17D2 in "programm_name.exe": Microsoft C++ exception:nlohmann:detail:parse_error at memorylocation 0x008FE65C

I'm sorry if this is an stupid error or mistake but I'm pretty new to programming.

[nlohmann]

The parser only throws an out_of_range error in case of number overflow. Can you share your JSON file, or check whether it contains numbers that cannot be expressed (e.g., really really large exponents)?

[david9472]

I tried different JSON files with different content but there is still the same error.
The JSON file I used looks like this:

{
  "device": [
    {
      "command": "resetInstruments",
      "statusCode": 0,
      "wait": 1000
    }
  ]
}

So there isn't any large number but it still throws an out_of_range error.

Just to make sure, this is the c++ code I use for printing out the JSON Object:

#include "pch.h"
#include "OwnUtil.h"
#include <iostream>
#include <sstream>
#include <fstream>
#include <Windows.h>
#include <stdio.h>
#include <SFML/Network.hpp>
#include <nlohmann/json.hpp>
#include <nlohmann/adl_serializer.hpp>

using json = nlohmann::json;
using namespace std;
int main()
{
	string text;
	json temp;
	ifstream read;
	read.open("response_resetinstruments.txt");
	getline(read, text);
	read.close();
	json in = json::parse(text);
	temp = in["/device/command/0"_json_pointer];
	cout << temp;
	```
I expected to get "resetInstruments" as an output in my console.

[nlohmann]

Firstly, you can immediately parse from an std::ifstream - just pass it to the parser like this:

std::ifstream read("response_resetinstruments.txt");
json in = json::parse(read);

Secondly, JSON Pointer /device/command/0 cannot be applied to the JSON value:

• /device accesses the array [ { "command": "resetInstruments", "statusCode": 0, "wait": 1000 } ]
• /command is then invalid, because in an array, you can only use integers.

To access "resetInstruments", the correct JSON Pointer would be /device/0/command.

[david9472]

Ok. I'm new to this so I want it as clear as possible. But still thank you for the improvement.

However, I applied what you mentioned above, and there is still the same error. It points to the out_of_range part in the json_sax headerfile.

[nlohmann]

This code works for me:

#include "json.hpp"
#include <iostream>
#include <fstream>

using json = nlohmann::json;

int main()
{
    std::ifstream read("response_resetinstruments.txt");
    json in = json::parse(read);
    auto temp = in["/device/0/command"_json_pointer];
    std::cout << temp << std::endl;
}

and outputs

"resetInstruments"

Can you try this code?

[david9472]

Copied your code, inserted it in my programm and I still get the same error. I just had to include "pch.h" and the headerfiles are one folder above, so I have to include #include "nlohmann/json.hpp". But the rest is exactly the same.

[nlohmann]

To rule out issues with the input file, can you try

#include "json.hpp"
#include <iostream>

using json = nlohmann::json;

int main()
{
    json in = R"({ "device": [ { "command": "resetInstruments", "statusCode": 0, "wait": 1000 } ] })"_json;
    auto temp = in["/device/0/command"_json_pointer];
    std::cout << temp << std::endl;
}

[david9472]

Sorry for not responting.
I had to add "pch.h" again but then it finally worked. Why isn't there any error message if I store the string directly into the JSON Obejct? And, even more important, what do I have to change in order to use some sort of .txt file or an response from another function as an imput?
Did I make some sort of mistake or did I overlook something?
Thanks in advance you really helpt me.

[nlohmann]

I do not understand your questions. Can you please be more specific?

[david9472]

I very appreciate that the code works if I directly store the String in the JSON variable.
However I need to parse a string which is just the return of a function. But if I use a variable I can‘t write R“(...);.
So do you have any additional Information or tips on how I can parse from a string variable instead of a string directly?

[nlohmann]

You can call json j = json::parse(your_string);

[david9472]

Thank you so much. You solved my problem now I can go to the next step in my project.