#include <fstream> 
#include <iostream>
#include <string>

int write_string_to_file_append(const std::string & file_string, const std::string str )
{
	std::ofstream	OsWrite(file_string,std::ofstream::app);
	OsWrite<<str;
	OsWrite<<std::endl;
	OsWrite.close();
   return 0;
}

int main()
{
	write_string_to_file_append(std::string("file.txt",std::string("1234567890")));
	return 0;
}