Implementing a Line Filter with C++ Ranges

Implementing a Line Filter by Using C++ Ranges

C++ ranges provide a simple and powerful way to filter a collection of data. A line filter is a common example that can be used to search for a specific string in a collection of lines. This tutorial will demonstrate how to use the C++ range library to implement a line filter.

The Problem

We have a collection of strings (e.g. lines of text from a file), and we need to find all the strings that contain a specified substring (e.g. a specific word).

The Solution

Using the C++ range library, we can create a range that contains only the strings that satisfy a certain condition, and then iterate over them. For this problem, we want to keep only the strings that contain the specified substring. To do this, we can use the std::string::find() method to check if a string contains a substring.

The Code

#include <algorithm>
#include <range/v3/all.hpp>

// Function to filter the lines
auto line_filter(const std::vector<std::string>& lines, const std::string& substring) {
  return lines | ranges::view::filter([&substring](const auto& line){
    return line.find(substring) != std::string::npos;
  });
}

// Main function
int main() {
  // Initialize the vector of lines
  std::vector<std::string> lines = {
    "This is a test",
    "This is also a test",
    "This is not a test"
  };

  // Call the line_filter function
  auto filtered_lines = line_filter(lines, "test");

  // Print out the filtered lines
  for (auto& line : filtered_lines) {
    std::cout << line << std::endl;
  }

  return 0;
}

In this code, we first define a line_filter() function, which takes a vector of lines and a string representing the substring we are looking for. We then use the C++ range library’s view::filter() method to filter out the lines that don’t contain the substring. Finally, we iterate over the filtered lines and print them out.

Conclusion

In this tutorial, we have seen how to use the C++ range library to implement a line filter. We first wrote a function that uses the view::filter() method to filter the given collection of strings, and then used it in a main() function to print out the filtered lines.