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Embedded C & C++ Tooling

cJSON Code Generator & C Struct Parser

Automatically generate ANSI C/C++ structs, deserialization parsers, serializers, null-checks, and memory-safe cJSON_Delete() routines directly from sample JSON. Designed for ESP32, STM32, Arduino, and low-level network microservices.

Sample JSON Input
Generated cJSON C Code

Developing with DaveGamble's cJSON in C and C++

When programming embedded hardware, firmware devices (like ESP32, ESP8266, STM32, Nordic nRF), or high-throughput C applications, parsing dynamic JSON payloads manually is error-prone and fraught with buffer overflows and memory leak risks. The cJSON library provides an elegant, battle-tested DOM representation of JSON entities in pure ANSI C.

1. Type-Safe Field Extraction

cJSON models values using a tagged union inside cJSON structs. To safely extract fields without segmentation faults, always test item presence and type tags: 

cJSON *item = cJSON_GetObjectItemCaseSensitive(root, "temperature");
if (cJSON_IsNumber(item)) {
    double temp = item->valuedouble;
}

2. Safe Dynamic Memory Management

Each call to cJSON_Parse() traverses the incoming string and allocates linked lists of cJSON structs using malloc(). To prevent memory leaks, you must invoke cJSON_Delete(root) exactly once when the entire parse tree is no longer needed.

3. String Buffering and Printing

When serializing C data structures back into JSON strings:

  • cJSON_Print(root): Outputs human-readable, formatted JSON with indentation and newlines.
  • cJSON_PrintUnformatted(root): Generates minified JSON with all extraneous whitespace stripped, ideal for HTTP POST payloads or MQTT telemetry transmissions.
  • Crucial: Remember to call cJSON_free(rendered_string) to free the buffer returned by cJSON_Print().

Frequently Asked Questions

cJSON is an ultra-lightweight, ANSI-C compliant JSON parser created by Dave Gamble. Because it is written in pure portable C89 with zero external dependencies, it is the de facto standard JSON library for embedded systems, microcontrollers (ESP32, STM32), IoT firmware, game engines, and performance-critical network daemons.
When calling cJSON_Parse() or cJSON_CreateObject(), heap memory is dynamically allocated. Developers must always call cJSON_Delete(root) on the root pointer once processing finishes to prevent memory leaks. Deleting a child node directly attached to a tree will cause double-free panics.
cJSON_GetObjectItem matches JSON keys in a case-insensitive manner, which can violate RFC 8259 JSON specifications. Modern best practice is to always use cJSON_GetObjectItemCaseSensitive() to guarantee strict case matching and avoid accidental key collisions.
Yes. The generated parsing and serialization routines adhere strictly to ANSI C89/C99 standards and only require standard libc headers (stdio.h, stdlib.h, string.h, stdbool.h) alongside cJSON.h.