Hi EveryBody, I am again here with a petty issue................ Please Help me, I am a newly born programmer to MFC To Write/Read structure on File, I wrote the following code. Code: /* [B]test[/B] is a structure defined in stdafx.h*/ /* struct [B]test[/B] { CString name; CString age; };*/ Code: void CFileOperationsDlg::OnBnClickedButton1() { this->UpdateData (TRUE); CFile f; CFileException Fexcep; test buffWrite; test buffRead; buffWrite .age ="27"; buffWrite .name = "My Name"; f.Open ("E:\\MyFile.bcr", CFile ::modeCreate | CFile ::modeWrite ,&Fexcep); f.Write (&buffWrite,sizeof(buffWrite )); f.Close (); if(f.Open("E:\\MyFile.bcr", CFile ::modeRead ,&Fexcep) == FALSE) return; try { f.Read (&buffRead ,sizeof(buffRead )); } catch(CException *e) { e->AssertValid (); } f.Close (); } The Following Exception occurs when the last statement in code executes......... Unhandled exception at 0x7c176d3f (mfc71d.dll) in FileOperations.exe: 0xC0000005: Access violation reading location 0xfeeefeee.
CString is a class, not a plain old data (POD) type so it behaves differently. The MFC way to deal with this is serialization. All MFC classes derived from CObject support serialization. This is a means of taking all the typically hierarchical data stored in a class structure and converting it to a linear format more appropriate for storing in a stream. You can lookup MSDN help on serialization for more information. Another approach is to convert the CString to POD types then store those in your file. Since CString is just a bunch of functions for string manipulation and a string buffer, a CString's complete state can be defined by the contents of it's buffer. The buffer is nothing more than a NULL terminated array of characters (either char or wchar_t depending on UNICODE settings--both POD types). You can go about this one of two ways: store an integral value representing the lenght of the string, then the characters themselves (this is sort-of how CString's internal Serialize() function works), or store all the characters and include the NULL terminator. There are advantages and disadvantages to both, so chose whichever is appropriate. A simple implementation based on your code might look like this (added code in green): Code: void CFileOperationsDlg::OnBnClickedButton1() { this->UpdateData (TRUE); CFile f; CFileException Fexcep; test buffWrite; test buffRead; [COLOR="SeaGreen"]size_t sz; TCHAR *buf;[/COLOR] buffWrite .age ="27"; buffWrite .name = "My Name"; f.Open ("E:\\MyFile.bcr", CFile ::modeCreate | CFile ::modeWrite ,&Fexcep); [COLOR="SeaGreen"]sz=buffWrite.GetLength(); f.Write(&sz,sizeof(size_t)); f.Write(buffWrite.GetBuffer(),sz*sizeof(TCHAR)); //[/COLOR]f.Write (&buffWrite,sizeof(buffWrite )); [COLOR="SeaGreen"]buffWrite.ReleaseBuffer();[/COLOR] f.Close (); if(f.Open("E:\\MyFile.bcr", CFile ::modeRead ,&Fexcep) == FALSE) return; try { [COLOR="SeaGreen"]f.Read(&sz,sizeof(size_t); buf=new TCHAR[sz+1]; f.Read(buf,sz*sizeof(TCHAR)); buf[sz]=0; buffRead.SetString(buf); delete[] buf; //[/COLOR]f.Read (&buffRead ,sizeof(buffRead )); } catch(CException *e) { e->AssertValid (); } f.Close (); }
many thanks for your response.i have done this work,But with the error I faced.please help me. 1>------ Build started: Project: teststring, Configuration: Debug Win32 ------ 1>Compiling... 1>teststringDlg.cpp 1>c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(214) : error C2228: left of '.GetLength' must have class/struct/union 1> type is 'TCHAR *' 1>c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(216) : error C2039: 'GetBuffer' : is not a member of 'test' 1> c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(13) : see declaration of 'test' 1>c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(218) : error C2039: 'ReleaseBuffer' : is not a member of 'test' 1> c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(13) : see declaration of 'test' 1>c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(227) : warning C4267: 'argument' : conversion from 'size_t' to 'UINT', possible loss of data 1>c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(229) : error C2039: 'SetString' : is not a member of 'test' 1> c:\documents and settings\zahra d\desktop\project\teststring\teststring\teststringdlg.cpp(13) : see declaration of 'test' 1>Build log was saved at "file://c:\Documents and Settings\zahra d\Desktop\Project\teststring\teststring\Debug\BuildLog.htm" 1>teststring - 4 error(s), 1 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
