https://blog.faceutil.com/2017/04/21/c%ec%96%b8%ec%96%b4-%eb%b0%94%ec%9d%b4%ed%8a%b8-%eb%8b%a8%ec%9c%84-%ed%8c%8c%ec%9d%bc-%ec%9d%bd%ea%b8%b0-fread-%e3%81%90/