How to Build a Text Editor from Scratch Using Build Your Own X

Question

Build a text editor from scratch with the Build Your Own X repository. Follow step-by-step guides for text buffering cursor management and terminal rendering in C and Rust.

Accepted Answer

You can build a text editor from scratch by following the curated tutorials in the codecrafters-io/build-your-own-x repository, which provide step-by-step guides for implementing core components including the text buffer, cursor management, and terminal rendering in languages like C and Rust.

The codecrafters-io/build-your-own-x repository contains a comprehensive collection of do-it-yourself programming tutorials. If you want to build a text editor from scratch, the repository links to language-specific guides that walk you through creating a functional terminal-based editor from the ground up, covering everything from raw terminal input to file persistence.

Core Architecture of a Text Editor

All text editor tutorials in the repository share a common architectural pattern. Understanding these five core components provides a reusable mental model that applies to any implementation language.

The Buffer

The buffer holds the file's contents in memory and supports insert and delete operations. According to the source analysis, typical implementations use a dynamic array of strings in C, a Vec<String> in Rust, or a mutable list in Python to store individual lines.

The Cursor

The cursor tracks the current row and column position, updating on user input. This is typically implemented as a simple (row, col) struct that responds to arrow-key events.

The Renderer

The renderer draws the buffer to the terminal and refreshes the display on changes. Implementations vary by language: C tutorials use direct ANSI escape code writes, while Rust tutorials leverage the crossterm library for terminal handling.

Input Handling

The input handler reads keystrokes and maps them to editor commands such as insert, delete, and navigation. This requires putting the terminal into raw mode using termios in C, crossterm in Rust, or tty in Python.

File I/O

File I/O handles loading files into the buffer on startup and writing changes back on save. Standard open/read/write system calls manage line endings and error handling.

Step-by-Step Implementation Guide

To build a text editor from scratch using the Build Your Own X guides, follow this progression:

Select a language - The README.md lists tutorials for C (Kilo) and Rust (Hecto), among others. Choose based on your comfort level.
Initialize your project - Create a new repository with git init, cargo init, or a Makefile.
Implement the buffer - Start with a resizable in-memory representation using dynamic arrays or vectors.
Add cursor logic - Store row and column state and update it based on arrow-key events.
Build the renderer - Write the buffer to the terminal, handling scrolling and status bar display.
Hook up input - Configure raw mode terminal input and map keys to editor actions.
Add persistence - Implement write (:w) and quit (:q) commands using standard file I/O.
Iterate and extend - Add syntax highlighting, multiple buffers, or GUI front-ends.

Code Example: Minimal Buffer Implementation in C

The "Kilo" tutorial linked in the repository provides a complete C implementation. Below is a condensed example demonstrating the buffer initialization and file loading logic as implemented in the guide.

/* buffer.c – core text buffer */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    char **lines;      // array of string lines
    size_t line_count;
    size_t capacity;
} Buffer;

/* Allocate an empty buffer */
Buffer *buffer_new(void) {
    Buffer *b = malloc(sizeof(Buffer));
    b->lines = NULL;
    b->line_count = 0;
    b->capacity = 0;
    return b;
}

/* Append a line, growing the array as needed */
void buffer_append_line(Buffer *b, const char *line) {
    if (b->line_count == b->capacity) {
        b->capacity = b->capacity ? b->capacity * 2 : 8;
        b->lines = realloc(b->lines, b->capacity * sizeof(char *));
    }
    b->lines[b->line_count++] = strdup(line);
}

/* Load a file into the buffer, splitting on '\n' */
void buffer_load_file(Buffer *b, const char *filename) {
    FILE *fp = fopen(filename, "r");
    if (!fp) return;               // error handling omitted for brevity
    char *line = NULL;
    size_t len = 0;
    while (getline(&line, &len, fp) != -1) {
        buffer_append_line(b, line);
    }
    free(line);
    fclose(fp);
}

/* Insert a character at a given row/col */
void buffer_insert(Buffer *b, size_t row, size_t col, char c) {
    if (row >= b->line_count) return;
    char *old = b->lines[row];
    size_t old_len = strlen(old);
    char *new = malloc(old_len + 2);   // +1 for new char, +1 for '\0'
    memcpy(new, old, col);
    new[col] = c;
    memcpy(new + col + 1, old + col, old_len - col + 1);
    free(old);
    b->lines[row] = new;
}

This scaffold provides the foundation for the cursor handling, screen drawing, and raw-mode input covered in the full tutorial.

Available Tutorials in Build Your Own X

The README.md file in the codecrafters-io/build-your-own-x repository contains direct links to complete editor implementations:

C – "Kilo": A minimal editor using only the standard library and raw terminal control via termios. This tutorial covers all five architectural components using ANSI escape codes for rendering.
Rust – "Hecto": A modern, type-safe implementation featuring clean modular design. This guide leverages the crossterm crate for cross-platform terminal handling.

Summary

Build Your Own X provides curated, language-specific tutorials for building text editors from scratch.
All implementations share five core components: a buffer for text storage, a cursor for position tracking, a renderer for display output, an input handler for keystrokes, and file I/O for persistence.
The Kilo (C) and Hecto (Rust) tutorials offer complete step-by-step guides ranging from dynamic memory allocation to raw terminal mode configuration.
Starting with the buffer implementation provides the foundation for adding cursor logic, rendering, and input handling.

Frequently Asked Questions

What programming languages are supported for building a text editor in Build Your Own X?

The repository primarily features tutorials for C and Rust. The C tutorial ("Kilo") uses standard library functions and termios for terminal control, while the Rust tutorial ("Hecto") utilizes modern crates like crossterm for cross-platform compatibility.

Do I need prior operating systems knowledge to build a text editor from scratch?

Basic familiarity with terminal concepts helps but is not required. The tutorials explain how to use termios in C or terminal libraries in Rust to handle raw mode input. You should understand pointers (for C) or ownership (for Rust) to manage the dynamic text buffer effectively.

How does the text buffer handle large files efficiently?

The buffer implementation uses dynamically expanding arrays. In the C example, buffer_append_line doubles the capacity (b->capacity * 2) when the array fills, ensuring amortized O(1) insertion time. Lines are stored as separate strings, allowing efficient insertion and deletion at specific row and column positions.

Can I extend these terminal editors into GUI applications?

Yes. The architectural principles—buffer management, cursor positioning, and file I/O—remain identical. You would replace the terminal renderer with a GUI framework (like GTK, Qt, or a web-based renderer) while keeping the core data structures intact. The Build Your Own X tutorials provide the foundational logic that ports to any UI framework.