Javier Jimenez

Posted on Nov 27

C++ on Ubuntu: Installation, Setup, and First Steps

#cpp #ubuntu #programming #tutorial

I recommend seeing first – installation of Homebrew and asdf on Ubuntu (it’s short, only 5 commands)

📘 Official Documentation

C++ - Reference on CPPReference
C++ - On DevDocs.io

⭐ Popular Frameworks (ordered from lower to higher learning curve)

⚠️ In C++ there are no standard “web frameworks” like in Python, but there are widely used libraries.

No Framework (POSIX sockets) — Minimalist, simple, native.
Crow — Inspired by Flask, very easy to use.
Boost.Beast — Fast and modern for HTTP/WebSocket.
CppRestSDK — Complete, Django/Express style.

🛠️ C++ Installation on Ubuntu

C++ already comes installed, but you should make sure you have g++:

sudo apt update
sudo apt install g++ build-essential

🍺 Installation with Homebrew

brew install gcc

📦 Standard Package Manager

C++ does not have an official manager like pip or npm, but the most used ones are:

apt (on Ubuntu)
vcpkg
conan

Check compiler version:

g++ --version

Install a JSON library (example):

sudo apt install nlohmann-json3-dev

🔧 Installation with ASDF

ASDF can compile specific versions of GCC/LLVM.

System dependencies:

sudo apt update
sudo apt install -y build-essential libssl-dev zlib1g-dev \
libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm \
libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev

Install plugin + version

asdf plugin add gcc
asdf install gcc 14.1.0
asdf global gcc 14.1.0

Example: .tool-versions

gcc 14.1.0

📝▶️ Create and run a C++ file

Create file:

touch hello.cpp

Contents of hello.cpp

#include <iostream>
int main() {
    std::cout << "Hola Mundo desde C++!\n";
    return 0;
}

💻 Compile and run locally:

g++ hello.cpp -o app-hello
./app-hello

🟦 Basic example in C++

🗂️🌐 Static file Web Server.

Note: C++ does not come with an integrated web server.
But you can create a very small one using POSIX sockets (no dependencies).

📝 Create file: touch server.cpp

📦 Contents of server.cpp

#include <iostream>
#include <string>
#include <regex>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>

std::string html_escape(const std::string& text) {
    std::string escaped = text;
    escaped = std::regex_replace(escaped, std::regex("&"), "&amp;");
    escaped = std::regex_replace(escaped, std::regex("<"), "&lt;");
    escaped = std::regex_replace(escaped, std::regex(">"), "&gt;");
    escaped = std::regex_replace(escaped, std::regex("\""), "&quot;");
    return escaped;
}

int main() {
    int server = socket(AF_INET, SOCK_STREAM, 0);

    sockaddr_in addr{};
    addr.sin_family = AF_INET;
    addr.sin_port = htons(8000);
    addr.sin_addr.s_addr = INADDR_ANY;

    bind(server, (sockaddr*)&addr, sizeof(addr));
    listen(server, 10);

    std::cout << "Server running at http://localhost:8000\n";

    while (true) {
        int client = accept(server, nullptr, nullptr);

        char buffer[2048] = {0};
        read(client, buffer, sizeof(buffer));
        std::string request(buffer);

        // Extract path
        size_t start = request.find("GET ");
        size_t end = request.find(" HTTP/");
        std::string path = request.substr(start + 4, end - (start + 4));

        // Get username
        std::string username = "guest";
        size_t qpos = path.find("?username=");
        if (qpos != std::string::npos) {
            username = path.substr(qpos + 10);
        }
        username = html_escape(username);

        // Generate HTML
        std::string content =
            "<!DOCTYPE html><html lang='es'><head><meta charset='UTF-8'>"
            "<title>Hello</title></head><body style='text-align:center'>"
            "<h1>Hello, " + username + "</h1></body></html>";

        std::string response =
            "HTTP/1.1 200 OK\r\n"
            "Content-Type: text/html\r\n"
            "Content-Length: " + std::to_string(content.size()) + "\r\n"
            "Connection: close\r\n\r\n" +
            content;

        send(client, response.c_str(), response.size(), 0);
        close(client);
    }
}

▶️ Compile and run

g++ server.cpp -o http-server
./http-server

👉 Visit:
http://localhost:8000/?username=Homero

⚙️🧩 JSON REST API

What it does:

Reads data from a data.json file
Exposes two endpoints:

List of characters at /characters
Data by ID at /characters/:id

Example file: data.json

[
  {
    "id": 1,
    "age": 39,
    "name": "Homer Tompson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/1.webp"
  },
  {
    "id": 2,
    "age": 39,
    "name": "Marge Simpson",
    "portrait_path": "https://cdn.thesimpsonsapi.com/500/character/2.webp"
  }
]

📝 Create file: touch api.cpp

▶️ File contents: api.cpp

This example uses the nlohmann/json library (header-only).
Install it on Ubuntu:

sudo apt install nlohmann-json3-dev

#include <iostream>
#include <fstream>
#include <string>
#include <regex>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

// Load JSON file
json load_characters() {
    std::ifstream f("data.json");
    json data;
    f >> data;
    return data;
}

std::string make_json_response(const json& data, int status=200) {
    std::string body = data.dump();
    return
        "HTTP/1.1 " + std::to_string(status) + " OK\r\n"
        "Content-Type: application/json\r\n"
        "Content-Length: " + std::to_string(body.size()) + "\r\n"
        "Connection: close\r\n\r\n" +
        body;
}

int main() {
    int server = socket(AF_INET, SOCK_STREAM, 0);

    sockaddr_in addr{};
    addr.sin_family = AF_INET;
    addr.sin_port = htons(7001);
    addr.sin_addr.s_addr = INADDR_ANY;

    bind(server, (sockaddr*)&addr, sizeof(addr));
    listen(server, 10);

    std::cout << "Server running at http://localhost:7001/characters\n";

    while (true) {
        int client = accept(server, nullptr, nullptr);

        char buffer[4096] = {0};
        read(client, buffer, sizeof(buffer));
        std::string request(buffer);

        size_t s = request.find("GET ");
        size_t e = request.find(" HTTP/");
        std::string path = request.substr(s + 4, e - (s + 4));

        json data = load_characters();

        // /characters
        if (path == "/characters") {
            auto res = make_json_response(data, 200);
            send(client, res.c_str(), res.size(), 0);
            close(client);
            continue;
        }

        // /characters/:id
        std::regex reg("^/characters/([0-9]+)$");
        std::smatch match;
        if (std::regex_match(path, match, reg)) {
            int id = std::stoi(match[1]);
            json found = nullptr;
            for (auto& c : data)
                if (c["id"] == id) found = c;

            if (!found.is_null()) {
                auto res = make_json_response(found, 200);
                send(client, res.c_str(), res.size(), 0);
            } else {
                auto res = make_json_response({{"error","Character not found"}}, 404);
                send(client, res.c_str(), res.size(), 0);
            }
            close(client);
            continue;
        }

        // Route not found
        json notfound = {
            {"error", "Route not found"},
            {"url_list", "http://localhost:7001/characters"},
            {"url_character", "http://localhost:7001/characters/1"}
        };
        auto res = make_json_response(notfound, 404);
        send(client, res.c_str(), res.size(), 0);

        close(client);
    }
}

▶️ Compile and run

g++ api.cpp -o api -std=c++17
./api

👉 Visit:
http://localhost:7001/characters

To test sanitization:
http://localhost:7001/characters/1

🟦 Extra example in C++

💻 GUI Calculator with QT

What it does:

Creates a small graphical calculator using Qt5.
Takes two numbers as input.
Provides four buttons: add, subtract, multiply, divide.
Displays the result inside the window.
Compiles using Qt5Widgets on Ubuntu.

To compile this file on Ubuntu:

# Install: 
sudo apt install qtbase5-dev

📝 Crear archivo: touch qt-calc.cpp

▶️ Contenido del archivo: qt-calc.cpp

#include <QApplication>
#include <QWidget>
#include <QLineEdit>
#include <QPushButton>
#include <QVBoxLayout>
#include <QHBoxLayout>
#include <QLabel>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    window.setWindowTitle("Calculadora Qt");

    // Inputs
    QLineEdit *input1 = new QLineEdit();
    QLineEdit *input2 = new QLineEdit();
    QLabel *result = new QLabel("Resultado: ");

    input1->setPlaceholderText("Número 1");
    input2->setPlaceholderText("Número 2");

    // Buttons
    QPushButton *btnAdd = new QPushButton("+");
    QPushButton *btnSub = new QPushButton("-");
    QPushButton *btnMul = new QPushButton("*");
    QPushButton *btnDiv = new QPushButton("/");

    // Horizontal layout for buttons
    QHBoxLayout *buttonsLayout = new QHBoxLayout();
    buttonsLayout->addWidget(btnAdd);
    buttonsLayout->addWidget(btnSub);
    buttonsLayout->addWidget(btnMul);
    buttonsLayout->addWidget(btnDiv);

    // Main layout
    QVBoxLayout *layout = new QVBoxLayout();
    layout->addWidget(input1);
    layout->addWidget(input2);
    layout->addLayout(buttonsLayout);
    layout->addWidget(result);
    window.setLayout(layout);

    // Helper function to calculate
    auto calc = [&](char op) {
        double a = input1->text().toDouble();
        double b = input2->text().toDouble();
        double r = 0;

        switch (op) {
            case '+': r = a + b; break;
            case '-': r = a - b; break;
            case '*': r = a * b; break;
            case '/': r = (b != 0) ? a / b : 0; break;
        }

        result->setText("Resultado: " + QString::number(r));
    };

    // Connect buttons
    QObject::connect(btnAdd, &QPushButton::clicked, [&]() { calc('+'); });
    QObject::connect(btnSub, &QPushButton::clicked, [&]() { calc('-'); });
    QObject::connect(btnMul, &QPushButton::clicked, [&]() { calc('*'); });
    QObject::connect(btnDiv, &QPushButton::clicked, [&]() { calc('/'); });

    window.show();
    return app.exec();
}

▶️ Compilar y correr

g++ qt-calc.cpp -o app-qt-calc -fPIC $(pkg-config --cflags --libs Qt5Widgets)

./app-qt-calc

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