CRichEdit打印问题

long CharRange = 0;

long LastChar = 0;//will store document length

FORMATRANGE fr;  //format range structure

::ZeroMemory(&fr, sizeof(FORMATRANGE));

fr.hdc = hdcPrinter;

fr.hdcTarget = hdcPrinter;          //Set member in FormatRange struct

//This bit here will get all the dimentions of the printer setup

int nHorizRes = dcPrinter.GetDeviceCaps(HORZRES),                 //width P in MM

nVertRes = dcPrinter.GetDeviceCaps(VERTRES),        //hight in raster lines

nLogPixelsX = dcPrinter.GetDeviceCaps(LOGPIXELSX),  //pixels per inch along x

nLogPixelsY = dcPrinter.GetDeviceCaps(LOGPIXELSY);  //pixels per inch along y

//set the printable area of printer in the FormatRange struct

fr.rcPage.left = 0; //these 2 mean top left

fr.rcPage.top = 0;

fr.rcPage.right = (nHorizRes/nLogPixelsX) * 1440;//these 2 mean bottom right

fr.rcPage.bottom = (nVertRes/nLogPixelsY) * 1440;    //equation changes pixel to TWIPS

// Set up some margins all around. Make them one inch

//results vary on printers depending on setup

fr.rc.left   = fr.rcPage.left + 1440;  // 1440 TWIPS = 1 inch.

fr.rc.top    = fr.rcPage.top + 1440;

fr.rc.right  = fr.rcPage.right - 1440;

fr.rc.bottom = fr.rcPage.bottom - 1440;

//select all text for printing

CHARRANGE cr;

cr.cpMin =0;

cr.cpMax = -1;//-1 selects all

fr.chrg = cr;//set this in FormatRange struct

//get length of document, used for more than one page

CharRange = m_RichEdit.GetTextLength();

long lNum = (long)ceil((float)CharRange/(float)m_RichEdit.FormatRange( &fr, TRUE ));	//total pages

for(long l = 0; l < lNum; l++)

{

	dcPrinter.StartPage();	///start the page



	LastChar = m_RichEdit.FormatRange( &fr, TRUE );//send text to DC, and record index of last fitting char

	cr.cpMin = LastChar;//Change charrange struct for next page

	cr.cpMax = CharRange; //using last char printed

	fr.chrg = cr;       //set that in formatrange struct



	dcPrinter.EndPage();

}

dcPrinter.EndDoc();

以上是部分代码，打印CRichEdit控件中的内容，用(long)ceil((float)CharRange/(float)m_RichEdit.FormatRange( &fr, TRUE ))计算总页数，有时打印多出一个空白页，有时没有空白页。
请问高手：
如何精确地计算出总页数；
或者用do-while循环如何设定循环结束的条件。