本文主要是介绍按行读取ANSI、UNICODE 、UNICODE big endian、UTF-8四种文本文,希望对大家解决编程问题提供一定的参考价值,需要的开发者们随着小编来一起学习吧!
代码简介
1.问题提出MFC提供的文件类CStdioFile,其中一个函数ReadString实现了文件的按行读取,但是不能满足不同类型的文本文件的按行读取,为了解决这一问题,笔者初步研究了一些编码知识,参考了网上的一些资料,实现了CStdioFile类的扩展类CStdioFileEx,完成了常见文本文件的按行读取(注明:不包括DOC、PDF等其他形式的文档).
在此对网上分享编码经验的网友表示感谢,同时由于我编写的类还未经过严格测试,如有错误或方法过于复杂敬请各位指正。
2.问题解决
(1)四种常见文本文件编码方式研究
ANSI、UNICODE 、UNICODE big endian、UTF-8四种格式编码存在差别,简要介绍如下:
ANSI编码:
无文件头(文件编码开头标志性字节)
ANSI编码字母数字占一个字节,汉字占两个字节,
回车换行符 单字节 十六进制表示为0d 0a
UNICODE编码:
文件头,十六进制表示为FF FE
每一个字符都用两个字节编码
回车换行符 双字节 000d 000a
Unicode big endian编码:
文件头十六进制表示为FE FF ,
后面编码是把字符的高位放在前面,低位放在后面,正好和Unicode编码颠倒。
回车换行符,双字节,十六进制表示为0d00 0a00
UTF-8 编码:
文件头,十六进制表示为EF BB BF。
UTF-8是Unicode的一种变长字符编码,数字、字母、回车、换行都用一个字节表示,汉字占3个字节.
回车换行符,单字节,十六进制表示为0d 0a
以中文"你好"二字为例,各种类型的编码对应的十六进制格式(可由EditPlus查看)如下图所示:
![](http://www.chengxuyuans.com/uploads/allimg/130531/1635493326-0.png)
由此可见上述的探讨是正确的。
(2)按行读取上述四种格式文本文件的解决方案
针对不同文件编码的特点,通过先检测文件头判断文件编码类型,然后根据文件类型分别调用不同的读取函数实现文件的按行读取。按行读取过程如下图所示:
![](http://www.chengxuyuans.com/uploads/allimg/130531/1635495961-1.png)
实现过程中,编写CStdioFileEx类,该类继承自CStdioFile类,覆盖了CStdioFile类的BOOL ReadString(CString& rString)方法,从而实现了文件按行读取。
代码片段
// StdioFileEx.h: interface for the CStdioFileEx class. // //#if !defined(AFX_STDIOFILEEX_H__C1F1F96B_9417_4388_8D24_892EDFA2A616__INCLUDED_) #define AFX_STDIOFILEEX_H__C1F1F96B_9417_4388_8D24_892EDFA2A616__INCLUDED_#if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 // -------------------------------------------------------------------------------------------- //程序用途:按行读取常见(包括ANSI、UNICODE、UNICODE big endian、UTF-8)格式的文本文件 //程序作者:湖北师范学院计算机科学与技术学院 王定桥 //核心算法:CStdioFileEx继承自CStdioFile, 覆盖CStdioFile的 BOOL ReadString(CString& rString)方法, // 根据不同文件编码特征,寻找文件回车换行符判断读取行结束,文件结束符判断文件结束 // 检测不同文件编码头部,获取文件类型后调用不同的读取函数 //测试结果:在Windows7 VC6.0环境下测试上述四种格式的txt文件通过 //尚未完成:未重载CStdioFile的 virtual LPTSTR ReadString( LPTSTR lpsz, UINT nMax )方法 // 未完成WriteString方法,未在VC UNICODE 环境下的测试 //制作时间:2012-04-19 //代码版权:代码公开供学习交流使用 欢迎指正错误 改善算法 // -------------------------------------------------------------------------------------------- #include "stdafx.h" //文本文件类型枚举值 typedef enum TextCodeType {UTF8=0,UNICODE =1,UNICODEBIGENDIAN=2,ANSI=3,FILEERROR=4 }TextCode; class CStdioFileEx :public CStdioFile { public:CStdioFileEx();CStdioFileEx(FILE* pOpenStream);CStdioFileEx(LPCTSTR lpszFileName, UINT nOpenFlags);virtual ~CStdioFileEx();virtual BOOL Open( LPCTSTR lpszFileName, UINT nOpenFlags, CFileException* pError = NULL); public://文件类型值转换到字符串CString FileTypeToString();//获取文件类型TextCode GetFileType();//按行读取文件BOOL ReadString(CString& rString);//静态方法 获取文件类型static TextCode GetFileType( LPCTSTR lpszFileName); protected:TextCode m_FileType;//保存文件类型const static int PREDEFINEDSIZE;//预定义一行文件所需空间 protected://从UTF-8文件按行读取BOOL ReadStringFromUTF8File(CString& rString);//从ANSI文件按行读取BOOL ReadStringFromAnsiFile(CString& rString);//重UNCIDOE、UNICODE big endian文件读取BOOL ReadStringFromUnicodeFile(CString& rString);//UTF-8字符串转换到UNICODE字符串CString UTF8ToUnicode(byte *szUTF8);//处理文件打开标志UINT ProcessFlags(LPCTSTR lpszFileName, UINT& nOpenFlags,TextCode &tc); };#endif // !defined(AFX_STDIOFILEEX_H__C1F1F96B_9417_4388_8D24_892EDFA2A616__INCLUDED_)
代码片段
// StdioFileEx.cpp: implementation of the CStdioFileEx class. // //#include "stdafx.h" #include "StdioFileEx.h"#ifdef _DEBUG #undef THIS_FILE static char THIS_FILE[]=__FILE__; #define new DEBUG_NEW #endif// // Construction/Destruction // /*static*/ const int CStdioFileEx::PREDEFINEDSIZE=1024; CStdioFileEx::CStdioFileEx():CStdioFile() {m_FileType=ANSI;//指定默认类型 } CStdioFileEx::CStdioFileEx(FILE* pOpenStream):CStdioFile(pOpenStream) {CString filepath=pOpenStream->_tmpfname;//? 尚不清楚File*结构m_FileType=GetFileType(filepath); } CStdioFileEx::CStdioFileEx(LPCTSTR lpszFileName, UINT nOpenFlags):CStdioFile(lpszFileName,ProcessFlags(lpszFileName, nOpenFlags,m_FileType) ) { } CStdioFileEx::~CStdioFileEx() {} // -------------------------------------------------------------------------------------------- //CStdioFileEx::GetFileType 静态方法 检测文本文件类型 // -------------------------------------------------------------------------------------------- /*static */ TextCode CStdioFileEx::GetFileType(LPCTSTR lpszFileName) {CFile file;byte buf[3];//unsigned charTextCode tc;try{if(file.Open(lpszFileName,CFile::modeRead|CFile::shareDenyNone|CFile::typeBinary)){ file.Read(buf,3);if(buf[0]==0xEF && buf[1]==0xBB && buf[2]==0xBF)tc=UTF8;elseif(buf[0]==0xFF && buf[1]==0xFE )tc=UNICODE ;elseif(buf[0]==0xFE && buf[1]==0xFF )tc=UNICODEBIGENDIAN;elsetc=ANSI;}elsetc=FILEERROR;}catch (CFileException ex){ CString errormsg;errormsg.Format(_T("操作文件%s时发生异常!"),ex.m_strFileName);AfxMessageBox(errormsg);}return tc; } // -------------------------------------------------------------------------------------------- //CStdioFileEx::Readstring 按行读取文本文件 //根据不同文件类型 调用不同的读取函数 // -------------------------------------------------------------------------------------------- BOOL CStdioFileEx::ReadString(CString& rString) { BOOL flag=FALSE;switch(m_FileType){case ANSI:flag=ReadStringFromAnsiFile(rString);break;case UNICODE:case UNICODEBIGENDIAN:flag=ReadStringFromUnicodeFile(rString);break;case UTF8:flag=ReadStringFromUTF8File(rString);break;case FILEERROR:flag=FALSE;break;default:break;}return flag; } // -------------------------------------------------------------------------------------------- //CStdioFileEx::ReadstringFromAnsiFile 从ANSI文件读取字符串 // -------------------------------------------------------------------------------------------- BOOL CStdioFileEx::ReadStringFromAnsiFile(CString& rString) { BOOL flag;try{ flag=CStdioFile::ReadString(rString);rString+="\r\n";}catch(CFileException ex){CString errormsg;errormsg.Format(_T("操作文件%s时发生异常!"),ex.m_strFileName);AfxMessageBox(errormsg);}return flag; } // -------------------------------------------------------------------------------------------- //CStdioFileEx::ReadstringFromUTF8File 从UTF8文件中按行读取 //由于UTF-8编码多字节编码且各种字符长度不同,判断回车换行需要判断连续两个字节 // -------------------------------------------------------------------------------------------- BOOL CStdioFileEx::ReadStringFromUTF8File(CString& rString) {long index;byte cr=0x0d;//回车换行符byte lf=0x0a;byte temp[2];byte tempbyte;byte *pbuf=new byte[PREDEFINEDSIZE+1];memset(pbuf,0,(PREDEFINEDSIZE+1)*sizeof(byte));UINT readlen;try{ //跳过文件头 移动文件指针if (m_pStream && ( GetPosition() == 0)){CStdioFile::Seek(3*sizeof(byte),CFile::begin);}index=0;do {memset(temp,0,2*sizeof(byte));readlen=CFile::Read(temp,2);//CStdioFile::Read效果不同 将省去回车符0x0dif(!readlen)return FALSE;//元素存贮到字节数组中pbuf[index++]=temp[0];pbuf[index++]=temp[1];tempbyte=temp[1];//判断回车换行if( ( tempbyte==cr && temp[0]==lf) ||(temp[0]==cr && temp[1]==lf))break;} while (readlen==2 && index<PREDEFINEDSIZE );pbuf[index]=0;rString=UTF8ToUnicode(pbuf);//UTF8编码转换到UNICODE}catch (CFileException ex){CString errormsg;errormsg.Format(_T("操作文件%s时发生异常!"),ex.m_strFileName);AfxMessageBox(errormsg);}delete[] pbuf;return TRUE; } // -------------------------------------------------------------------------------------------- //从UNICODE、UNICODE big endian文件按行读取 //当读取字节小于请求值(文件结束)或者超过预定义空间时无条件退出循环 //wChLine存放每行字符,wchtemp存放临时读取字符 //当编码为UNICODE big endian 时交换高低字节 ,将其转换成UNICODE字符串 // -------------------------------------------------------------------------------------------- BOOL CStdioFileEx::ReadStringFromUnicodeFile(CString& rString) {long index;UINT readlen;wchar_t wchcr=MAKEWORD(0x0d,0x00);;//回车符 MakeWord(低、高字节顺序) wchar_t wchlf=MAKEWORD(0x0a,0x00);wchar_t *wChLine=new wchar_t[PREDEFINEDSIZE+1];memset(wChLine,0,(PREDEFINEDSIZE+1)*sizeof(wchar_t));wchar_t wchtemp[2];BOOL flag=TRUE;try{ //跳过文件头 移动文件指针if (m_pStream && ( GetPosition() ==0)){Seek(2*sizeof(byte),CFile::begin);}index=0;do{ memset(wchtemp,0,2*sizeof(wchar_t));readlen=CFile::Read(wchtemp,sizeof(wchar_t)*2);//CStdioFile::Read效果不同if(!readlen)break;//UNICODE big endian交换高低字节if(UNICODEBIGENDIAN==m_FileType){ unsigned char high, low;high = (wchtemp[0] & 0xFF00) >>8;low = wchtemp[0] & 0x00FF;wchtemp[0] = ( low <<8) | high;high = (wchtemp[1] & 0xFF00) >>8;low = wchtemp[1] & 0x00FF;wchtemp[1] = ( low <<8) | high;}wChLine[index++]=wchtemp[0];wChLine[index++]=wchtemp[1];//判断回车换行if(wchtemp[0]==wchcr && wchtemp[1]==wchlf)break;}while( (readlen==sizeof(wchar_t)*2) && index<PREDEFINEDSIZE );wChLine[index]=0;CString strtext(wChLine,index);rString=strtext;if(rString.IsEmpty())flag=FALSE;}catch (CFileException ex){CString errormsg;errormsg.Format(_T("操作文件%s时发生异常!"),ex.m_strFileName);AfxMessageBox(errormsg);}delete[] wChLine;return flag; } // -------------------------------------------------------------------------------------------- //CStdioFileEx::UTF8ToUnicode UTF-8字符串转换成UNICODE字符串 // -------------------------------------------------------------------------------------------- CString CStdioFileEx::UTF8ToUnicode(byte *szUTF8) { CString strret;strret=_T("");if(!szUTF8)return strret;//获取转换后所需串空间的长度 int wcsLen = MultiByteToWideChar(CP_UTF8,0,(LPSTR)szUTF8,strlen((char*)szUTF8),NULL,0);LPWSTR lpw=new WCHAR[wcsLen+1]; if(!lpw)return strret;memset(lpw,0,(wcsLen+1)*sizeof(wchar_t)); //实施转换MultiByteToWideChar(CP_UTF8,0, (LPSTR)szUTF8, strlen((char *)szUTF8), (LPWSTR)lpw, wcsLen); CString str(lpw);delete[] lpw;return str; } // -------------------------------------------------------------------------------------------- //CStdioFileEx::GetFileType获取文件类型 // -------------------------------------------------------------------------------------------- TextCode CStdioFileEx::GetFileType() { return m_FileType; } // -------------------------------------------------------------------------------------------- //CStdioFileEx::FileTypeToString 文件类型枚举值转换为字符串值 // -------------------------------------------------------------------------------------------- CString CStdioFileEx::FileTypeToString() { CString strtype;switch(m_FileType){case ANSI:strtype.Format("%s",_T("ANSI"));break;case UTF8:strtype.Format("%s",_T("UTF8"));break;case UNICODE:strtype.Format("%s",_T("UNICODE"));break;case UNICODEBIGENDIAN:strtype.Format("%s",_T("UNICODE big endian"));break;case FILEERROR:strtype.Format("%s",_T("FILEERROR"));break;default:break;}return strtype; } // -------------------------------------------------------------------------------------------- //CStdioFileEx::Open 重载父类的文件打开操作 改变不同类型文件的打开方式 // -------------------------------------------------------------------------------------------- BOOL CStdioFileEx::Open( LPCTSTR lpszFileName, UINT nOpenFlags, CFileException* pError) { ProcessFlags(lpszFileName,nOpenFlags,m_FileType);//处理文件打开方式return CStdioFile::Open(lpszFileName, nOpenFlags,pError); } // -------------------------------------------------------------------------------------------- //CStdioFileEx::ProcessFlags 处理不同文件的打开方式 //ANSI文件采用文本读取,UNICODE、UNICDOE big endian、UTF-8采用二进制方式读取 // -------------------------------------------------------------------------------------------- UINT CStdioFileEx::ProcessFlags(LPCTSTR lpszFileName, UINT& nOpenFlags,TextCode &tc) {tc=CStdioFileEx::GetFileType(lpszFileName);if ((nOpenFlags & CFile::modeReadWrite)|| (nOpenFlags & CFile::modeRead) ){switch(tc){case ANSI:nOpenFlags|= CFile::typeText;nOpenFlags&=~CFile::typeBinary;break;case UTF8:nOpenFlags |= CFile::typeBinary;nOpenFlags&= ~CFile::typeText;break;case UNICODE:nOpenFlags |= CFile::typeBinary;nOpenFlags&= ~CFile::typeText;break;case UNICODEBIGENDIAN:nOpenFlags |= CFile::typeBinary;nOpenFlags&= ~CFile::typeText;break;case FILEERROR:break;default:break;}}nOpenFlags|=CFile::shareDenyNone;return nOpenFlags; }
代码片段
void CReadStringDlg::OnBtnOpen() {// TODO: Add your control notification handler code herechar szFilter[] = "Text Files (*.txt)|*.txt|All Files (*.*)|*.*||";CFileDialog filedlg(TRUE , "txt", NULL, OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT, szFilter,this);if(IDOK==filedlg.DoModal()){m_strPath=filedlg.GetPathName();UpdateData(FALSE);m_ctrlEdit.SetSel(0,-1);m_ctrlEdit.Clear();if(m_stdiofileex.Open(m_strPath,CFile::modeRead)){m_strFileType=m_stdiofileex.FileTypeToString();UpdateData(FALSE);}else{MessageBox(_T("读取文件失败!"));}} } //读取文件 void CReadStringDlg::OnBtnRead() {// TODO: Add your control notification handler code hereif(!ValidateInput())return;CString strread,strtemp;m_ctrlEdit.GetWindowText(strread);m_ctrlEdit.SetSel(0,-1);m_ctrlEdit.Clear();if(m_stdiofileex.m_pStream){ int cnt=0;strread+="\r\n";while(cnt<m_lLineCnt){if(m_stdiofileex.ReadString(strtemp)){ strread+=strtemp;cnt++;}else{ AfxMessageBox(_T("读取已经到达文件末尾!"));break;}}m_ctrlEdit.SetSel(0,-1);m_ctrlEdit.ReplaceSel(strread);}else{MessageBox(_T("读取文件失败!"));} } //验证输入 BOOL CReadStringDlg::ValidateInput() {UpdateData();if(m_strPath.IsEmpty()){MessageBox("文件路径为空,请填写!");return FALSE;}if(m_lLineCnt<=0)return FALSE;return TRUE; }
代码片段
PTSTR Normalise(PBYTE pBuffer) {PTSTR ptText; // pointer to the text char* or wchar_t* depending on UNICODE settingPWSTR pwStr; // pointer to a wchar_t bufferint nLength; // a useful integer variable// obtain a wide character pointer to check BOMspwStr = reinterpret_cast<PWSTR>(pBuffer);// check if the first word is a Unicode Byte Order Markif (*pwStr == 0xFFFE || *pwStr == 0xFEFF){// Yes, this is Unicode dataif (*pwStr++ == 0xFFFE){// BOM says this is Big Endian so we need// to swap bytes in each word of the textwhile (*pwStr){// swap bytes in each word of the bufferWCHAR wcTemp = *pwStr >> 8;wcTemp |= *pwStr << 8;*pwStr = wcTemp;++pwStr;}// point back to the start of the textpwStr = reinterpret_cast<PWSTR>(pBuffer + 2);} #if !defined(UNICODE)// This is a non-Unicode project so we need// to convert wide characters to multi-byte// get calculated buffer sizenLength = WideCharToMultiByte(CP_UTF8, 0, pwStr, -1, NULL, 0, NULL, NULL);// obtain a new buffer for the converted charactersptText = new TCHAR[nLength];// convert to multi-byte charactersnLength = WideCharToMultiByte(CP_UTF8, 0, pwStr, -1, ptText, nLength, NULL, NULL); #elsenLength = wcslen(pwStr) + 1; // if Unicode, then copy the input textptText = new WCHAR[nLength]; // to a new output buffernLength *= sizeof(WCHAR); // adjust to size in bytesmemcpy_s(ptText, nLength, pwStr, nLength); #endif}else{// The text data is UTF-8 or Ansi #if defined(UNICODE)// This is a Unicode project so we need to convert// multi-byte or Ansi characters to Unicode.// get calculated buffer sizenLength = MultiByteToWideChar(CP_UTF8, 0, reinterpret_cast<PCSTR>(pBuffer), -1, NULL, 0);// obtain a new buffer for the converted charactersptText = new TCHAR[nLength];// convert to Unicode charactersnLength = MultiByteToWideChar(CP_UTF8, 0, reinterpret_cast<PCSTR>(pBuffer), -1, ptText, nLength); #else// This is a non-Unicode project so we just need// to skip the UTF-8 BOM, if presentif (memcmp(pBuffer, "\xEF\xBB\xBF", 3) == 0){// UTF-8pBuffer += 3;}nLength = strlen(reinterpret_cast<PSTR>(pBuffer)) + 1; // if UTF-8/ANSI, then copy the input textptText = new char[nLength]; // to a new output buffermemcpy_s(ptText, nLength, pBuffer, nLength); #endif}// return pointer to the (possibly converted) text buffer.return ptText; }
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