C++ Primer 4/e在File Input and Output這個地方有一個警告：『For historical reasons, the IO library uses C-style character strings (Section 4.3, p. 130) rather than C++ strings to refer to file names. When we call open or use a file name as the initializer when creating an fstream object, the argument we pass is a C-style string, not a library string. Often our programs obtain file names by reading the standard input. As usual, it is a good idea to read into a string, not a C-style character array. Assuming that the name of the file we wish to use is in a string, we can use the c_str member (Section 4.3.2, p. 139) to obtain a C-style string.』
中文版的這樣寫：『由於歷史因素，IO程式庫使用C-style字元字串（4.3節.p.130）表示檔案名稱，而非使用C++ strings。當我們呼叫open()或在建立fstream物件時以檔名為初值，傳遞時的引數都必須是C-style字串而不是程式庫定義的strings。應用程式經常需要從標準輸入裝置取得檔名，把它讀入string是個好主意，不要讀入C-style字元array：假設我們想使用的檔名內含於某個string，可運用string提供的c_str()（4.3.2節，p.139）獲得C-style字串。』
對喔！之前一直讀到C-style的字串的問題，現在在file IO看到有差異的地方了，看來規定還是相沿已久來的傳統，不得不簽救救習慣啊！