Test schrieb:
> How can I do this?

With software.

Sorry forget the information...it's in esp8266 code

I need this in an Arduino code..

Use string functions: 
https://www.arduino.cc/reference/en/language/variables/data-types/stringobject/

Hannes J. schrieb:
> https://stedolan.github.io/jq/manual/

I guess that won't run on an esp8266. But anyway, here is an example for 
sh:

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echo [[2,3],[5,6]] | jq -c [.[],[7,8]]

Test schrieb:
> I want to read it in an array and add one pair [7,8].

You can write a simple JSON parser that does just that. Or you use a 
general JSON parsing library and construct your data structure with it. 
I guess adding the additional pair does not require any JSON business.

KR, Sebastian

Hello i tried it

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#include <iostream>

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#include "ArduinoJson.h"

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int main() {

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  StaticJsonDocument<300> doc;

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  char json[] =

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      "[[48.756080,2.302038],[48.756080,2.302038]]";

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  DeserializationError error = deserializeJson(doc, json);

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  if (error) {

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    std::cerr << "deserializeJson() failed: " << error.c_str() << std::endl;

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    return 1;

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  }

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  double longitude = doc[0];

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  // Print values.

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    std::cout << longitude << std::endl;

But the output is 0. WHat is wrong??