[json.exception.type_error.304] cannot use at() with array - works in windows, fails in linux (gcc)

[calvinwiii-flpds]

I cannot get past error 304 cannot use at()
code runs fine when compiled for windows, but fails when compiled on a raspi with gcc.

I've tried streamstrings, strings, removing the defines and coding directly

#define MQTT_LIVEVIEW_STATION_TAG "stationId"
#define MQTT_LIVEVIEW_TIME_TAG "timeStamp"
#define MQTT_LIVEVIEW_ACTION_TAG "action"
#define MQTT_LIVEVIEW_DURATION_TAG "duration"

struct LIVE_VIEW_REQUESTA
{
std::string stationId;
std::string timeStamp;
std::string action;
int duration;
};

void to_json(json& j, const LIVE_VIEW_REQUESTA& A)
{
j = json{ {MQTT_LIVEVIEW_STATION_TAG,A.stationId},
{ MQTT_LIVEVIEW_TIME_TAG,A.timeStamp},
{ MQTT_LIVEVIEW_ACTION_TAG,A.action},
{ MQTT_LIVEVIEW_DURATION_TAG,A.duration}
};
}

void from_json(const json& j, LIVE_VIEW_REQUESTA& A)
{
j.at(MQTT_LIVEVIEW_STATION_TAG).get_to(A.stationId);
j.at(MQTT_LIVEVIEW_TIME_TAG).get_to(A.timeStamp);
j.at(MQTT_LIVEVIEW_ACTION_TAG).get_to(A.action);
j.at(MQTT_LIVEVIEW_DURATION_TAG).get_to(A.duration);
}

int main(void)
{
LIVE_VIEW_REQUESTA live_view_requesta;

auto text = R"( { "timeStamp" : "2025-06-17T20:01:23.4156036+00:00", "stationId" : "FL_LAK_1", "action" : "start", "duration" : 10 } )";

json Doc{ json::parse(text) };

try {
Doc.get_to(live_view_requesta);
}
catch (const std::exception& e)
{
std::cout << e.what();
// [json.exception.type_error.304] cannot use at() with object
}

[nlohmann]

See https://json.nlohmann.me/home/faq/#brace-initialization-yields-arrays

[calvinwiii-flpds]

and the solution when I don't have control of the incoming json? the code snip-it is part of a parser where the json source is the cloud

[nlohmann]

Replace

json Doc{ json::parse(text) };

with

json Doc = json::parse(text) ;

[calvinwiii-flpds]

Much appreciated, particularly considering the late hour. that change seems to have corrected the problem Calvin Winey - Mechanical Engineer / Programmer - Finish Line PDS A Better Way for Small Companies to Develop Products e | ***@***.*** p | 603 769-7547 (cell) w | www.FinishLinePDS.com 94 River Rd | Hudson, NH | 03051 Click for Product Development White Papers<http://www.finishlinepds.com/documents.php>

…

________________________________ From: Niels Lohmann ***@***.***> Sent: Wednesday, June 18, 2025 2:28 AM To: nlohmann/json ***@***.***> Cc: Calvin Winey ***@***.***>; Author ***@***.***> Subject: Re: [nlohmann/json] [json.exception.type_error.304] cannot use at() with array - works in windows, fails in linux (gcc) (Discussion #4824) Replace json Doc{ json::parse(text) }; with json Doc = json::parse(text) ; — Reply to this email directly, view it on GitHub<#4824 (reply in thread)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AYS7MKZFQ6GO5OSISB5F6OT3EEBIBAVCNFSM6AAAAAB7RQ5M7OVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTGNJQGQZTQMQ>. You are receiving this because you authored the thread.Message ID: ***@***.***>