Easy to read and write the JSON file

Posted on: October 1, 2024 in C programme ,

In C, you can handle JSON data by using libraries such as cJSON or json-c. Below is a basic example of how to create, write, and read a JSON file using the cJSON library.

Step-by-step:

Install cJSON Library

If you’re using a Linux-based system, you can install cJSON with:

command

sudo apt-get install libcjson-dev

Manual Installation

Download cJSON:

Go to the cJSON GitHub repository.
Download the ZIP file of the repository or clone it:

c

git clone https://github.com/DaveGamble/cJSON.git

Build cJSON:

Open the cJSON folder and navigate to the cJSON directory.
You may need to create a Visual Studio project or a Makefile project depending on your development setup.
If you are using CMake, you can create a CMake build

c

mkdir build
cd build
cmake ..
cmake --build .

Include cJSON in Your Project:

After building, ensure that the cJSON.h and cJSON.c files are included in your project.
In your C code, include cJSON as shown

c

#include "cJSON.h"

2. Code to Create and Write JSON

This code demonstrates how to create a JSON object and write it to a file:

c

#include <stdio.h>
#include <stdlib.h>
#include "cJSON.h"

int main() {
    // Create a JSON object
    cJSON *root = cJSON_CreateObject();

    // Add values to the JSON object
    cJSON_AddStringToObject(root, "name", "John Doe");
    cJSON_AddNumberToObject(root, "age", 30);
    cJSON_AddStringToObject(root, "occupation", "Software Developer");

    // Create an array and add it to the object
    cJSON *skills = cJSON_CreateArray();
    cJSON_AddItemToArray(skills, cJSON_CreateString("C"));
    cJSON_AddItemToArray(skills, cJSON_CreateString("JavaScript"));
    cJSON_AddItemToArray(skills, cJSON_CreateString("Python"));
    cJSON_AddItemToObject(root, "skills", skills);

    // Print the JSON object as a string
    char *json_string = cJSON_Print(root);
    printf("Generated JSON:\n%s\n", json_string);

    // Write JSON string to a file
    FILE *file = fopen("data.json", "w");
    if (file) {
        fprintf(file, "%s", json_string);
        fclose(file);
        printf("\nJSON saved to data.json\n");
    } else {
        printf("Failed to open file for writing\n");
    }

    // Free memory
    cJSON_Delete(root);
    free(json_string);

    return 0;
}

3. Code to Read JSON from a File

The following code reads the JSON file we created:

c

#include <stdio.h>
#include <stdlib.h>
#include "cJSON.h"

void read_json_file(const char *filename) {
    FILE *file = fopen(filename, "r");
    if (!file) {
        printf("Could not open file %s for reading\n", filename);
        return;
    }

    // Get the file size
    fseek(file, 0, SEEK_END);
    long length = ftell(file);
    fseek(file, 0, SEEK_SET);

    // Allocate memory to store the content
    char *content = (char *)malloc(length + 1);
    fread(content, 1, length, file);
    fclose(file);
    content[length] = '\0'; // Null-terminate the string

    // Parse the JSON content
    cJSON *root = cJSON_Parse(content);
    if (!root) {
        printf("Error parsing JSON file\n");
        free(content);
        return;
    }

    // Extract values from the JSON object
    const cJSON *name = cJSON_GetObjectItem(root, "name");
    const cJSON *age = cJSON_GetObjectItem(root, "age");
    const cJSON *occupation = cJSON_GetObjectItem(root, "occupation");

    printf("Name: %s\n", name->valuestring);
    printf("Age: %d\n", age->valueint);
    printf("Occupation: %s\n", occupation->valuestring);

    // Free the JSON object and memory
    cJSON_Delete(root);
    free(content);
}

int main() {
    read_json_file("data.json");
    return 0;
}

Explanation:

Creating JSON: We use cJSON_CreateObject() to create a JSON object, and add data to it using cJSON_AddStringToObject() and cJSON_AddNumberToObject().
Writing to File: The generated JSON string is written to a file using fopen() and fprintf().
Reading JSON: We read the file’s contents into memory and parse it using cJSON_Parse(). Then we extract values using cJSON_GetObjectItem().

Compilation:

You need to link the cJSON library when compiling:

c

gcc -o json_example json_example.c -lcjson

Note: If you prefer manual installation, ensure you have the necessary C compiler and development tools installed, such as Visual Studio or MinGW

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