Find the oldest or newest DateTime filename in a directory

	DIR *directory1;
	struct dirent *entry1;
	string filename;
	string filename_name;
	string filename_extension;
	uint64_t this_file_value;
	uint64_t selected_file_value;
	string selected_file_name;
	stringstream ss1;
	
	//This function looks for the oldest or newest filename, our filenames that are created using YYYYMMDDHHMMSS.extension format so it simply
	//converts their names to numeric and does a compare

	printf("Starting work through directory for next livedata file...\n");
	//selected_file_value = 0xffffffffffff;				//<Use for oldest file
	selected_file_value = 0;					//<Use for newest file
	directory1 = opendir("/home/pi/myfolder");			//Open a directory stream
	if (directory1 != NULL)
	{
		while (entry1 = readdir(directory1))
		{
			if (entry1->d_type == DT_REG)			//DT_REG=regular file, DT_DIR=directory
			{
				printf("File: %s\n", entry1->d_name);
				filename = entry1->d_name;
				size_t dot = filename.find_last_of(".");
				if (dot != std::string::npos)
				{
					filename_name = filename.substr(0, dot);
					filename_extension  = filename.substr(dot, filename.size() - dot);

					if (filename_extension.compare(".txt") == 0)		//0=strings are the same
					{
						//We have: "2015092110" & ".extension"
						//We want: 2015092110

						printf("File: %s\n", filename_name.c_str());

						ss1.clear();
						ss1.str(std::string());
						ss1 << filename_name;
						ss1 >> this_file_value;
						if ((this_file_value > 0) && (this_file_value > selected_file_value))			//<<<Oldest or newest check here
						{
							//This file is older/newer than any previously found
							selected_file_value = this_file_value;
							selected_file_name = filename_name;
							printf("New selected file: %s\n", selected_file_name.c_str());
						}
					}
				}
			}

		}
	}
	closedir(directory1);

	if ((selected_file_value == 0xffffffffffff) || (selected_file_value == 0))
	{
		//-------------------------
		//----- NO FILE FOUND -----
		//-------------------------
		printf("No valid filename found - exiting\n");
		return(0);
	}
	
	//We have:
	//	selected_file_name			//Filename without the extension