A simple C++ class that reads files in a directory, and also works as an example of RAII.

DirectoryException.cpp

#include "DirectoryException.h"

DirectoryException::DirectoryException(const std::string& what_arg)
    : std::logic_error(what_arg) {
}

DirectoryException.h

#ifndef DIRECTORYEXCEPTION_H
#define DIRECTORYEXCEPTION_H


#include <stdexcept>

class DirectoryException : public std::logic_error {
 public:
  explicit DirectoryException(const std::string& what_arg);
};


#endif  // DIRECTORYEXCEPTION_H

DirectoryReader.cpp

#include "DirectoryException.h"
#include "DirectoryReader.h"

DirectoryReader::DirectoryReader(std::string path)
    : dir_(opendir(path.c_str())) {
  if (dir_ == NULL) {
    throw DirectoryException("Can't open directory");
  }
}

DirectoryReader::~DirectoryReader() {
  closedir(dir_);
}

std::vector<std::string> DirectoryReader::files() const {
  std::vector<std::string> files;
  struct dirent *ent;
  while ((ent = readdir(dir_)) != NULL) {
    if (ent->d_type == DT_REG) {  // regular file
      files.push_back(ent->d_name);
    }
  }

  return files;
}

DirectoryReader.h

#ifndef DIRECTORYREADER_H
#define DIRECTORYREADER_H

#include <dirent.h>
#include <vector>


class DirectoryReader {
 public:
  explicit DirectoryReader(std::string path);
  ~DirectoryReader();
  std::vector<std::string> files() const;

 private:
  DIR *dir_;
};


#endif  // DIRECTORYREADER_H