Scraping Multiple Pages in C++ with cpp-netlib and cppxpath

Oct 15, 2023 · 4 min read

Web scraping is useful to programmatically extract data from websites. Often you need to scrape multiple pages from a site to gather complete information. In this article, we'll see how to scrape multiple pages in C++ using the cpp-netlib and cppxpath libraries.

Prerequisites

To follow along, you'll need:

  • Basic C++ knowledge
  • A C++ compiler
  • cpp-netlib and cppxpath libraries
  • Include Libraries

    We'll need the following header files:

    #include <netlib.http>
    #include <pugixml.hpp>
    

    Define Base URL

    We'll scrape a blog - https://copyblogger.com/blog/. The page URLs follow a pattern:

    <https://copyblogger.com/blog/>
    <https://copyblogger.com/blog/page/2/>
    <https://copyblogger.com/blog/page/3/>
    

    Let's define the base URL pattern:

    std::string baseUrl = "<https://copyblogger.com/blog/page/{}/>";
    

    The {} allows us to insert the page number.

    Specify Number of Pages

    Next, we'll specify how many pages to scrape. Let's scrape the first 5 pages:

    int numPages = 5;
    

    Loop Through Pages

    We can now loop from 1 to numPages and construct the URL for each page:

    for (int page = 1; page <= numPages; page++) {
    
      // Construct page URL
      std::string url = boost::str(boost::format(baseUrl) % page);
    
      // Code to scrape each page
    
    }
    

    Send Request and Parse HTML

    Inside the loop, we'll send a GET request and parse the HTML:

    netlib::http::client client;
    netlib::http::client::request request(url);
    auto response = client.get(request);
    
    pugi::xml_document doc;
    doc.load(response.body());
    

    This gives us an XML document to extract data from.

    Extract Data

    Now within the loop we can use doc and XPath to find and extract data from each page.

    For example, to get all article elements:

    auto articles = doc.select_nodes("//article");
    

    We can loop through articles and extract information like title, URL, author etc.

    Full Code

    Our full code to scrape 5 pages is:

    #include <netlib.http>
    #include <pugixml.hpp>
    
    int main() {
    
      std::string baseUrl = "<https://copyblogger.com/blog/page/{}/>";
      int numPages = 5;
    
      for (int page = 1; page <= numPages; page++) {
    
        std::string url = boost::str(boost::format(baseUrl) % page);
    
        netlib::http::client client;
        netlib::http::client::request request(url);
        auto response = client.get(request);
    
        pugi::xml_document doc;
        doc.load(response.body());
    
        auto articles = doc.select_nodes("//article");
    
        for (auto& article : articles) {
    
          // Extract data from article
    
          auto title = article.select_node("./h2[@class='entry-title']").node().text();
          auto url = article.select_node("./a[@class='entry-title-link']/@href").node().value();
          auto author = article.select_node("./div[@class='post-author']/a").node().text();
    
          std::vector<std::string> categories;
          for (auto& cat : article.select_nodes("./div[@class='entry-categories']/a")) {
            categories.push_back(cat.node().text());
          }
    
          // Print extracted data
          std::cout << "Title: " << title << "\\n";
          std::cout << "URL: " << url << "\\n";
          std::cout << "Author: " << author << "\\n";
          for (auto& cat : categories) {
            std::cout << "Category: " << cat << "\\n";
          }
          std::cout << "\\n";
    
        }
    
      }
    
    }
    

    This allows us to scrape and extract data from multiple pages sequentially. The code can be extended to scrape any number of pages.

    Summary

  • Use a base URL pattern with {} placeholder
  • Loop through pages with for loop
  • Construct each page URL
  • Send request and parse HTML
  • Extract data using XPath
  • Print or store scraped data
  • Web scraping enables collecting large datasets programmatically. With the techniques here, you can scrape and extract information from multiple pages of a website in C++.

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