How to get file extension using C++?

There are two ways to get the file extension in C++: Use the string manipulation function std::find to find the extension delimiter. Use the extension function from the boost::filesystem::path class in the Boost library.

How to get file extension in C++

Getting file extension in C++ can help you:

• Identify and process different file types
• Verify that the input file name has a valid extension
• Implement file archiving and management

Method 1: Use string operations

You can use the standard library function std::find to find the last dot (i.e. extension separator) in the file path.

#include <iostream>
#include <string>

std::string get_file_extension(const std::string& filename) {
  auto last_dot = filename.find_last_of('.');
  if (last_dot == std::string::npos) {
    return "";  // 没有扩展名
  }
  return filename.substr(last_dot + 1);
}

int main() {
  std::string filename = "example.txt";
  std::cout << "File extension: " << get_file_extension(filename) << std::endl;
  return 0;
}

Method 2: Use boost::filesystem

If you are using the Boost library, you can use boost::filesystem extension function in ::path class.

#include <boost/filesystem.hpp>

std::string get_file_extension(const std::string& filename) {
  boost::filesystem::path path(filename);
  return path.extension().string();
}

int main() {
  std::string filename = "example.txt";
  std::cout << "File extension: " << get_file_extension(filename) << std::endl;
  return 0;
}

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