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How to parse and read JSON file correctly?

Hi guys,

I am using the nRF52832 board and I want to parse and read my JSON file. I don't have too much experience working with cJSON and here you will find my simple code where I try to understand how to define things properly. I will appreciate a lot if you can help me with some advice or better if you can suggest me where I made errors.

Best regards,

Adnan.

/*
 * Copyright (c) 2012-2014 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr.h>
#include <sys/printk.h>
#include <string.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <float.h>
#include <limits.h>
#include <ctype.h>
#include "cJSON.h"


char *create_hello(void) {
	
	char *string;
	
	cJSON *hello = cJSON_CreateObject();
	
	cJSON *functionName = cJSON_CreateString("hello_world");
	cJSON_AddItemToObject(hello, "functionName", functionName);
	
	string = cJSON_Print(hello);
	
	cJSON_Delete(hello);
	return string;
	
	}

void hello_world (void) {
	
	printk("Hello World! %s\n", CONFIG_BOARD);
	}


void main(void)
{
	const char *hello = "{\"functionName\": \"hello_world\"}";
	cJSON *hello_json = cJSON_Parse(hello);
	cJSON *functionName = cJSON_GetObjectItemCaseSensitive(hello_json, "functionName");
	
	while(true){
		
		if (functionName == "hello_world") {
			hello_world();
			k_sleep(K_SECONDS(1));
			}		
			
		}
}

  • Hello, Aduka!

    Thank you for reaching out. First of all, have you defined the correct prj.conf for your application? Mine looks like this for the hello_world sample:

    # nothing here
    CONFIG_CJSON_LIB=y
    
    # newlibc
    CONFIG_NEWLIB_LIBC=y

    Secondly, your code is mostly correct, but you have done an illegal comparison in your while loop. Look at my main below, where the error is corrected:

    void main(void)
    {
    	const char *hello = "{\"functionName\": \"hello_world\"}";
    	cJSON *hello_json = cJSON_Parse(hello);
    	char* functionName = cJSON_Print(cJSON_GetObjectItemCaseSensitive(hello_json, "functionName"));
    	
    	while(true){
    		
    		if (strcmp(functionName, "hello_world")) {
    			hello_world();
    			k_sleep(K_SECONDS(1));
    			}		
    			
    		}
    }

    In the code above I have changed line 45 so that cJSON_Print is used to write the content to a string. Then I have changed 49 to use strcmp, for comparing the strings. The line numbers I reference are from your original code. 

    Hope this helps you on your way, and please reach out if you wonder about anything else. 

    Best regards,
    Carl Richard

  • Hi Carl,

    Thanks a lot for this help and suggestions! I tried this code with these corrections, but again I am not able to compile it on my board. Now the problem occurs in my proj.conf file I think.

    This is the error:

    error: Aborting due to Kconfig warnings

    CMake Error at /home/adnan/zephyrproject/zephyr/cmake/kconfig.cmake:217 (message):
    command failed with return code: 1
    Call Stack (most recent call first):
    /home/adnan/zephyrproject/zephyr/cmake/app/boilerplate.cmake:510 (include)
    /home/adnan/zephyrproject/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:24 (include)
    /home/adnan/zephyrproject/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:40 (include_boilerplate)
    CMakeLists.txt:5 (find_package)


    -- Configuring incomplete, errors occurred!
    See also "/home/adnan/zephyrproject/zephyr/build/CMakeFiles/CMakeOutput.log".
    See also "/home/adnan/zephyrproject/zephyr/build/CMakeFiles/CMakeError.log".
    FAILED: build.ninja
    /usr/bin/cmake --regenerate-during-build -S/home/adnan/zephyrproject/zephyr/samples/hello_world_cjson -B/home/adnan/zephyrproject/zephyr/build
    ninja: error: rebuilding 'build.ninja': subcommand failed
    FATAL ERROR: command exited with status 1: /usr/bin/cmake --build /home/adnan/zephyrproject/zephyr/build

    Can you maybe figure out what could be a potential problem now? And also, I forgot to tell that I use Zephyr if that is important for this problem. Also, my last question is related to Makefile and prj.conf files...where I can find the proper configuration for different samples. For sure, I will need to use cJSON together with my BLE example.

    Thanks in advance and best regards,

    Adnan.

  • Hello again, Adnan!

    I see. Could you provide the whole log? You may have to run the build command with "pristine" to ensure that the new config is applied. Like this:

    west build -b nrf52dk_nrf52832 -p

    ----

    For your second question. You should not need to use Makefiles at all. The two configs above, as well as #include "cJSON.h" should suffice. For BLE samples I suggest looking at what we have in <ncs_root>/nrf/samples/bluetooth/.

    Best regards,
    Carl Richard

  • Hi Carl,

    I tried this and again unsuccessfully. This is the whole message after I tried to compile this sample: 

    west build -b nrf52dk_nrf52832 -p
    -- west build: generating a build system
    Including boilerplate (Zephyr base): /home/adnan/zephyrproject/zephyr/cmake/app/boilerplate.cmake
    -- Application: /home/adnan/zephyrproject/zephyr/samples/hello_world_cjson
    -- Zephyr version: 2.3.0-rc1 (/home/adnan/zephyrproject/zephyr)
    -- Found Python3: /usr/bin/python3.6 (found suitable exact version "3.6.9") found components: Interpreter
    -- Board: nrf52dk_nrf52832
    ZEPHYR_TOOLCHAIN_VARIANT not set, trying to locate Zephyr SDK
    -- Found toolchain: zephyr (/home/adnan/zephyr-sdk-0.11.3)
    -- Found west: /home/adnan/.local/bin/west (found suitable version "0.7.2", minimum required is "0.7.1")
    -- Found dtc: /home/adnan/zephyr-sdk-0.11.3/sysroots/x86_64-pokysdk-linux/usr/bin/dtc (found suitable version "1.5.0", minimum required is "1.4.6")
    -- Found BOARD.dts: /home/adnan/zephyrproject/zephyr/boards/arm/nrf52dk_nrf52832/nrf52dk_nrf52832.dts
    -- Generated zephyr.dts: /home/adnan/zephyrproject/zephyr/samples/hello_world_cjson/build/zephyr/zephyr.dts
    -- Generated devicetree_unfixed.h: /home/adnan/zephyrproject/zephyr/samples/hello_world_cjson/build/zephyr/include/generated/devicetree_unfixed.h
    Parsing /home/adnan/zephyrproject/zephyr/Kconfig
    Loaded configuration '/home/adnan/zephyrproject/zephyr/boards/arm/nrf52dk_nrf52832/nrf52dk_nrf52832_defconfig'
    Merged configuration '/home/adnan/zephyrproject/zephyr/samples/hello_world_cjson/prj.conf'

    /home/adnan/zephyrproject/zephyr/samples/hello_world_cjson/prj.conf:2: warning: attempt to assign the value 'y' to the undefined symbol CJSON_LIB

    error: Aborting due to Kconfig warnings

    CMake Error at /home/adnan/zephyrproject/zephyr/cmake/kconfig.cmake:217 (message):
    command failed with return code: 1
    Call Stack (most recent call first):
    /home/adnan/zephyrproject/zephyr/cmake/app/boilerplate.cmake:510 (include)
    /home/adnan/zephyrproject/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:24 (include)
    /home/adnan/zephyrproject/zephyr/share/zephyr-package/cmake/ZephyrConfig.cmake:35 (include_boilerplate)
    CMakeLists.txt:5 (find_package)


    -- Configuring incomplete, errors occurred!
    FATAL ERROR: command exited with status 1: /usr/bin/cmake -B/home/adnan/zephyrproject/zephyr/samples/hello_world_cjson/build -S/home/adnan/zephyrproject/zephyr/samples/hello_world_cjson -GNinja -DBOARD=nrf52dk_nrf52832

    And also thanks a lot for this advice for BLE example.

    I hope that you will be able to help me again!

    Best regards,

    Adnan.

  • Thank you for the log. 

    First of all it seems like you haven't defined the ZEPHYR_TOOLCHAIN_VARIANT correctly. For our devices it is gnuarmemb, so depending on your system please set the toolchain variant. 

    Secondly, are you using Zephyr standalone, or our the nRF Connect SDK? 

    Best regards,
    Carl Richard

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