Downloading Images from a Website with C++ and cpp-selector

In this article, we will learn how to use C++ and the cpp-httplib and cpp-selector libraries to download all the images from a Wikipedia page.

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Overview

The goal is to extract the names, breed groups, local names, and image URLs for all dog breeds listed on this Wikipedia page. We will store the image URLs, download the images and save them to a local folder.

Here are the key steps we will cover:

Include required headers
Send HTTP request to fetch the Wikipedia page
Parse the page HTML using cpp-selector
Find the table with dog breed data using a CSS selector
Iterate through the table rows
Extract data from each column
Download images and save locally
Print/process extracted data

Let's go through each of these steps in detail.

Includes

We need these headers:

#include <httplib.h>
#include <selector/selector.h>
#include <fstream>

httplib - Sends HTTP requests

selector - Parses HTML/XML

fstream - File I/O

Send HTTP Request

To download the web page:

httplib::Client cli("commons.wikimedia.org");

auto res = cli.Get("/wiki/List_of_dog_breeds",
  {{"User-Agent", "cpp-httplib"}});

if(res) {
  // Parse HTML
}

We make a GET request and provide a custom user-agent.

Parse HTML

To parse the HTML:

pugi::xml_document doc;
doc.load(res->body.c_str());

auto html = doc.child("html");

The pugi::xml_document represents parsed HTML.

Find Breed Table

We use a CSS selector to find the table element:

auto table = html.select_node("table.wikitable.sortable").node();

This selects the

with the required CSS classes.

Iterate Through Rows

We loop through the rows:

for (auto& row : table.select_nodes("tr")) {

  // Extract data

}

We iterate through

elements within the table.

Extract Column Data

Inside the loop, we get the column data:

auto cells = row.select_nodes("td, th");

auto name = cells[0].child("a").text().get();
auto group = cells[1].text().get();

auto localNameNode = cells[2].select_node("span");
auto localName = localNameNode.text().get("");

auto img = cells[3].select_node("img");
auto photograph = img.attribute("src").value();

We use text() and attribute() methods to extract data.

Download Images

To download and save images:

if (!photograph.empty()) {

  auto img_data = cli.Get(photograph.c_str());

  std::ofstream file("dog_images/" + name + ".jpg", std::ios::binary);
  file << img_data->body;

}

We reuse the HTTP client and write image bytes to a file.

Store Extracted Data

We store the extracted data:

names.push_back(name);
groups.push_back(group);
localNames.push_back(localName);
photographs.push_back(photograph);

The vectors can then be processed as needed.

And that's it! Here is the full code:

// Includes
#include <httplib.h>
#include <selector/selector.h>
#include <fstream>
#include <vector>

// Vectors to store data
std::vector<std::string> names;
std::vector<std::string> groups;
std::vector<std::string> localNames;
std::vector<std::string> photographs;

// HTTP client
httplib::Client cli("commons.wikimedia.org");

// Send request
auto res = cli.Get("/wiki/List_of_dog_breeds",
  {{"User-Agent", "cpp-httplib"}});

if(res) {

  // Parse HTML
  pugi::xml_document doc;
  doc.load(res->body.c_str());

  auto html = doc.child("html");

  // Find table
  auto table = html.select_node("table.wikitable.sortable").node();

  // Iterate rows
  for (auto& row : table.select_nodes("tr")) {

    // Get cells
    auto cells = row.select_nodes("td, th");

    // Extract data
    auto name = cells[0].child("a").text().get();
    auto group = cells[1].text().get();

    auto localNameNode = cells[2].select_node("span");
    auto localName = localNameNode.text().get("");

    auto img = cells[3].select_node("img");
    auto photograph = img.attribute("src").value();

    // Download image
    if (!photograph.empty()) {

      auto img_data = cli.Get(photograph.c_str());

      std::ofstream file("dog_images/" + name + ".jpg", std::ios::binary);
      file << img_data->body;

    }

    // Store data
    names.push_back(name);
    groups.push_back(group);
    localNames.push_back(localName);
    photographs.push_back(photograph);

  }

}

This provides a complete C++ solution using cpp-httplib and cpp-selector to scrape data and images from HTML tables. The same approach can apply to many websites.

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