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emJSON - JSON for embedded systems

emJSON is a fast and memory efficient JSON library for embedded systems, written in C99

There are two libraries in this project. You may use either one, depending on your favor:

  • json.h: Low-level JSON library that does not use dynamic memory allocation (e.g. malloc().)
  • emJSON.h : Easy-to-use JSON library that is built open json.h functions and makes use of dynamic memory allocation.

Features

  • JSON Encoding.
  • JSON Decoding.
  • Easy to use.
  • Fast and efficient hash map algorithm.
  • Minimized use of memory and memory fragmentation by using only a single buffer.
  • No use of malloc() (json.h only)
  • No extra library dependencies. (Only C standard libraries used.)
  • Only need to include a single file (emJSON.h or json.h)

Simple Examples

json.h:

char str_input[] = "{\"sensor1\":0.045600,\"message\":\"JSON Is Cool\",\"sensor2\":142}";

char buffer[256];
json_t test = json_init(buffer, 256, 4);  // 4 is table size, this MUST be power of 2.
json_parse(&test, str_input);

float sensor1 = json_get_float(&test, "sensor1"); // 0.0456
int   sensor2 = json_get_int(&test, "sensor2");   // 142
char *message = json_get_str(&test, "message");   // "JSON Is Cool"

json_insert_int(&test, "intInput", 999); // insert

char str[80];
json_strcpy(str, &test);
printf("%s\n", str);
// {"sensor1":0.045600,"intInput":999,"message":"JSON Is Cool","sensor2":142}

emJSON.h:

char str_input[] = "{\"sensor1\":0.045600,\"message\":\"JSON Is Cool\",\"sensor2\":142}";

// The difference to json.h is emJSON does not require declaring buffer. 
json_t test = emJSON_init();  // 8 is table size
emJSON_parse(&test, str_input);

float sensor1 = emJSON_get_float(&test, "sensor1"); // 0.0456
int   sensor2 = emJSON_get_int(&test, "sensor2");   // 142
char *message = emJSON_get_str(&test, "message");   // "JSON Is Cool"

emJSON_insert_int(&test, "intInput", 999); // insert

char *str = emJSON_string(&test);
printf("%s\n", str);
// {"sensor1":0.045600,"intInput":999,"message":"JSON Is Cool","sensor2":142}

free(str);
// emJSON.h objects needs to be freed after used instead.
emJSON_free(&test);

Supported Devices

  • Arduino and AVR Microcontrollers (tested using Arduino Uno)
  • 32-bit ARM Cortex-M devices
    • NUCLEO-F4xx series (tested in mbed platform)
    • Other Cortex-M MCUs should work too.
  • x86 and x86-64 based general purpose computers (such as Windows/Linux/Unix computers.)

How To Use

All you need is the header and source files in emJSON folder. You may also want to see documentations in doc folder before you get started. For testing and using existing sample codes, please look at examples folder.