Method Write

source/TextIO.cpp:418–556

DWORD TextStream::Write(LPCTSTR aBuf, DWORD aBufLen)
// Returns the number of bytes aBuf took after performing applicable EOL and
// code page translations.  Since data is buffered, this is generally not the
// amount actually written to file.  Returns 0 on apparent critical failure,
// even if *some* data was written into the buffer and/or to file.
{
	if (!PrepareToWrite())
		return 0;

	if (aBufLen == 0)
	{
		aBufLen = (DWORD)_tcslen(aBuf);
		if (aBufLen == 0) // Below may rely on this having been checked.
			return 0;
	}
	
	DWORD bytes_flushed = 0; // Number of buffered bytes flushed to file; used to calculate our return value.

	LPCTSTR src;
	LPCTSTR src_end;
	int src_size;
	
	union {
		LPBYTE	dst;
		LPSTR	dstA;
		LPWSTR	dstW;
	};
	dst = mBuffer + mLength;
	
	// Allow enough space in the buffer for any one of the following:
	//	a 4-byte UTF-8 sequence
	//	a UTF-16 surrogate pair
	//	a carriage-return/newline pair
	LPBYTE dst_end = mBuffer + TEXT_IO_BLOCK - 4;

	for (src = aBuf, src_end = aBuf + aBufLen; ; )
	{
		// The following section speeds up writing of ASCII characters by copying as many as
		// possible in each iteration of the outer loop, avoiding certain checks that would
		// otherwise be made once for each char.  This relies on the fact that ASCII chars
		// have the same binary value (but not necessarily width) in every supported encoding.
		// EOL logic is also handled here, for performance.  An alternative approach which is
		// tidier and performs almost as well is to add (*src != '\n') to each loop's condition
		// and handle it after the loop terminates.
		if (mCodePage != CP_UTF16)
		{
			for ( ; src < src_end && !(*src & ~0x7F) && dst < dst_end; ++src)
			{
				if (*src == '\n' && (mFlags & EOL_CRLF) && ((src == aBuf) ? mLastWriteChar : src[-1]) != '\r')
					*dstA++ = '\r';
				*dstA++ = (CHAR)*src;
			}
		}
		else
		{
#ifdef UNICODE
			for ( ; src < src_end && dst < dst_end; ++src)
#else