cJSON Complete Documentation

cJSON is a lightweight C library used to parse and generate JSON data. It is widely used in embedded systems like ESP32 due to its small size and simplicity.

git clone https://github.com/davegamble/cjson

#include "cJSON.h"

cJSON *root = cJSON_CreateObject();

cJSON_AddStringToObject(root, "name", "John");
cJSON_AddNumberToObject(root, "age", 25);

char *json = cJSON_Print(root);
printf("%s\n", json);

cJSON_Delete(root);
free(json);

char *data = "{\"name\":\"John\",\"age\":25}";

cJSON *root = cJSON_Parse(data);

cJSON *name = cJSON_GetObjectItem(root, "name");

printf("%s\n", name->valuestring);

cJSON_Delete(root);

cJSON *arr = cJSON_CreateArray();

cJSON_AddItemToArray(arr, cJSON_CreateNumber(10));
cJSON_AddItemToArray(arr, cJSON_CreateNumber(20));

cJSON *root = cJSON_CreateObject();
cJSON *addr = cJSON_CreateObject();

cJSON_AddStringToObject(addr, "city", "Kolkata");

cJSON_AddItemToObject(root, "address", addr);

cJSON_ReplaceItemInObject(root, "age", cJSON_CreateNumber(30));

if (cJSON_IsString(name)) {
    printf("Valid\n");
}

• Always use cJSON_Delete()
• Free strings using free()
• Avoid memory leaks

cJSON *root = cJSON_CreateObject();
cJSON_AddNumberToObject(root, "temp", 28.5);

char *json = cJSON_PrintUnformatted(root);

// send via HTTP

cJSON_Delete(root);
free(json);

cJSON *cJSON_CreateObject(void);

cJSON *cJSON_CreateArray(void);

cJSON *cJSON_CreateString(const char *string);

cJSON *cJSON_CreateNumber(double num);

cJSON *cJSON_CreateBool(cJSON_bool b);

cJSON *cJSON_GetObjectItem(const cJSON *, const char *);

cJSON *cJSON_GetArrayItem(const cJSON *, int);

int cJSON_GetArraySize(const cJSON *);

cJSON_AddItemToObject()

cJSON_AddItemToArray()

cJSON_ReplaceItemInObject()

cJSON_DeleteItemFromObject()

char *cJSON_Print(const cJSON *);

char *cJSON_PrintUnformatted(const cJSON *);

void cJSON_Delete(cJSON *);