fgetws 讀取Unicode文件 (zz.IS2120@BG57IV3)

//z 2012-11-22 18:48:32 IS2120@BG57IV3.T2690489747.K[T4,L45,R0,V24]

fgetws 讀取Unicode文件

fgetws _fgetts 读取 中文 乱码 unicode 双字节 多字节

最近要讀取一個unicode文件做額外處理，但是透過 fgetws 去讀取檔案，利用WriteConsole顯示在console畫面卻無法正常顯示中文，查了好一陣子終於發現問題了；也就是在開啟檔案時你不可以使用 text mode去開啟檔案，必須透過binary mode開啟，這樣fgetws才會把檔案當作是unicode檔，也就是讀取時，會一次讀兩個bytes且不做任何轉換。

當你用text mode開啟時，fgetws會假設input stream是multibyte characters，所以會做 MBCS-to-Unicode 轉換。當你用text 開啟檔案用 fgetws讀取資料時，你會發現明明是一個中文字，但是讀取後會分開放到你設定的buffer中,例如下面，但是實際上我們期望的是0x540d。
buf[0] = 0x000d
buf[1] = 0x0054

//z 2012-11-22 18:50:40 IS2120@BG57IV3.T1612787755.K[T5,L47,R1,V24]
這也是為啥讀出後直接丟給WriteConsole卻無法顯示中文的問題。

所以如果要處理unicode的檔案請使用 binary mode開啟，詳細解說你以參考 MSND 的
Unicode™ Stream I/O in Text and Binary Modes 文件。

ex:

FILE *inputfp;
const _TCHAR *pfilename = _T("MY UNICODE FILE");

//Don't use text mode to read a UNICODE file if you want use fgetws to read data from file.
errno_t err = _tfopen_s(&inputfp, pfilename, _T("rb"));

_fgetts(Msgbuf, MAX_BUF_SIZE, inputfp);

DWORD dwCharWritten(0UL);

WriteConsole (GetStdHandle(STD_OUTPUT_HANDLE),
                             Msgbuf,
                             static_cast (_tcsclen(Msgbuf)),
                             &dwCharWritten,
                             NULL);

[Keyword]
_fgetts unicode file
//z 2012-11-22 18:50:40 IS2120@BG57IV3.T1612787755.K[T5,L47,R1,V24]

When a Unicode stream I/O routine (such as fwprintf, fwscanf, fgetwc, fputwc, fgetws, or fputws) operates on a file that is open in text mode (the default), two kinds of character conversions take place:

• Unicode-to-MBCS or MBCS-to-Unicode conversion. When a Unicode stream-I/O function operates in text mode, the source or destination stream is assumed to be a sequence of multibyte characters. Therefore, the Unicode stream-input functions convert multibyte characters to wide characters (as if by a call to the mbtowc function). For the same reason, the Unicode stream-output functions convert wide characters to multibyte characters (as if by a call to the wctomb function).
• Carriage return – linefeed (CR-LF) translation. This translation occurs before the MBCS – Unicode conversion (for Unicode stream input functions) and after the Unicode – MBCS conversion (for Unicode stream output functions). During input, each carriage return – linefeed combination is translated into a single linefeed character. During output, each linefeed character is translated into a carriage return – linefeed combination.

However, when a Unicode stream-I/O function operates in binary mode, the file is assumed to be Unicode, and no CR-LF translation or character conversion occurs during input or output. Use the _setmode( _fileno( stdin ), _O_BINARY ); instruction in order to correctly use wcin on a UNICODE text file.