Note

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cJSON Example

Introduction

This example demonstrates the use of cJSON on the K230 RT-Smart platform. cJSON is an ultra-lightweight, portable ANSI C JSON parser consisting of only two files, cJSON.c and cJSON.h, making it well suited for embedded environments.

Feature Description

cJSON provides complete JSON parsing and generation capabilities:

• JSON Parsing: Supports parsing JSON data from strings or files

• JSON Generation: Supports building JSON objects and outputting them as formatted strings

• Object Operations: Supports adding, deleting, modifying, and querying various JSON types, including arrays, objects, strings, numbers, and booleans

• Preallocated Printing: Supports printing with preallocated buffers to reduce memory fragmentation

• Memory Management: Provides a hook mechanism that allows users to customize memory allocators

Example Features

The example runs the complete official cJSON test suite, covering the following scenarios:

• Creation and parsing of JSON objects and arrays

• Handling of strings, numbers, booleans, and null

• Construction and traversal of nested structures

• Formatted and unformatted printing

• Printing with preallocated buffers

• Error handling and boundary condition tests

• Performance testing (optional)

Code Location

• Library source: src/rtsmart/libs/3rd-party/cjson/cJSON/

• Sample source: src/rtsmart/examples/3rd-party/cjson/cjson_basic/

Usage Instructions

Compilation Method

Firmware Compilation

At the root directory of the K230 RTOS SDK, use make menuconfig to configure the compilation options:

1. Enter RT-Smart 3rd-party Configuration → enable Enable Build cJSON

2. Enter the sample configuration → enable Enable Build cJSON Sample Programs

Then compile the firmware.

Standalone Compilation

Enter the cJSON sample directory and use the Makefile for compilation:

cd src/rtsmart/examples/3rd-party/cjson/cjson_basic
make

After successful compilation, the executable file will be generated.

Running Example

Copy the compiled executable to the development board, enter the directory where it is stored, and run:

./test_cjson

Viewing Results

After the program runs, it will execute the complete cJSON test suite and output something similar to the following:

cJSON Test Suite
================

Testing cJSON_Version()
[PASS] version check

Testing print_preallocated
[PASS] preallocated print matches normal print

Testing object creation and manipulation
[PASS] object add
[PASS] object replace
[PASS] array size
[PASS] parse number

...

===== Test Summary =====
Passed: XX
Failed:  0
=======================
All tests passed!

Common API Examples

#include "cJSON.h"

// Parse a JSON string
const char *json_str = "{\"name\":\"K230\",\"version\":1}";
cJSON *root = cJSON_Parse(json_str);
if (root == NULL) {
    const char *err = cJSON_GetErrorPtr();
    printf("Parse error at: %s\n", err);
}

// Read a field
cJSON *name = cJSON_GetObjectItem(root, "name");
if (cJSON_IsString(name)) {
    printf("name: %s\n", name->valuestring);
}
cJSON *ver = cJSON_GetObjectItem(root, "version");
if (cJSON_IsNumber(ver)) {
    printf("version: %d\n", ver->valueint);
}

// Build a JSON object
cJSON *new_obj = cJSON_CreateObject();
cJSON_AddStringToObject(new_obj, "device", "K230");
cJSON_AddNumberToObject(new_obj, "uptime", 3600);
char *output = cJSON_Print(new_obj);
printf("%s\n", output);

// Free
cJSON_Delete(root);
cJSON_Delete(new_obj);
free(output);

Configuration Description

Kconfig Option	Description
RTSMART_3RD_PARTY_ENABLE_CJSON	Compile the cJSON library (libcjson.a)

Dependencies

• cJSON has no external dependencies and can be used independently

• libpeer depends on cJSON: RTSMART_3RD_PARTY_ENABLE_LIBPEER automatically selects cJSON

Tip

cJSON provides only a single .c and .h file, and the source code can be directly copied into any C project. For detailed information about the cJSON API and best practices, please refer to cJSON GitHub.