be based on MFC How to read and write a single document

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Writing documents

Expected effect ：

When you click OK, pop up “ Whether to replace ” Prompt box , It refers to whether to replace the content in the original text .

1. Add corresponding menus and ID

Add the corresponding menu and its... In the menu bar ID, And in view.cpp Add the corresponding event handling function

2. Improve the corresponding event response function

This is how we write file function code

void Cdraw3View::OnWriteFile(){    // What to write     CString str = _T("hello,world");    // Open the file dialog ,TRUE For reading ,FALSE For writing     CFileDialog fileDlg(FALSE);    // Determine whether the user clicks OK or cancel     if (IDOK == fileDlg.DoModal()) {        // Get the file name returned by the dialog         CString fileName = fileDlg.GetPathName();        // Open file , Open in write mode , Create... If it doesn't exist         CFile file(fileName, CFile::modeWrite | CFile::modeCreate);        // write file , The first parameter is the write content , The second parameter is the length of the written content         file.Write(str, str.GetLength());        // Close file         file.Close();    }}

3. Conduct commissioning test

This code is written into the open file hello,world, However, after execution, we opened the document and found that it was not completely written , But only a part of it

This is because our compiler uses unicode code , and unicode The encoded English characters occupy two bytes , The length of the characters we pass in the write function can only write half of the characters to the file

4. Make corresponding modifications according to the test results

Change the length by × One sizeof(TCHAR),TCHAR yes MFC A type definition specified , If it is unicode Character set ,TCHAR It's two bytes ; Other modes may be a byte

// write file , The first parameter is the write content , The second parameter is the length of the written content file.Write(str, str.GetLength()*sizeof(TCHAR));

Debug and test again

Reading documents

Expected effect

1. Add an event response function for reading files

2. Improve the code of event response function

void Cdraw3View::OnReadFile(){    CFileDialog fileDlg(TRUE);    if (IDOK == fileDlg.DoModal()) {        // Get file path         CString path = fileDlg.GetPathName();        // Open as read-only         CFile file(path, CFile::modeRead);        // Set a read buffer         TCHAR* pBuf;        // Get the length of the file content         int cnt = file.GetLength();        // According to sizeof(TCHAR), Calculate how many characters there are         int chars = cnt / sizeof(TCHAR);        // Allocate a size for the buffer ,+1 The operation is to add a terminator at the end         pBuf = new TCHAR[chars + 1];        // The first is where to put the read content , The second is the read length         file.Read(pBuf, cnt);        // ending + A terminator         pBuf[chars] = 0;        // Pop up the read content         MessageBox(pBuf);        // Close file         file.Close();        // Free the requested space after closing the document         delete[] pBuf;    } }

3. Debug test  

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