File Content replacement-depressing results

Today, I want to write a small program that replaces a row of files in batches,

The initial idea is to operate directly in the file (not generate new files), so write the following code (operate on a single file)

1. /*
2. String m_strrepsrc; // The identifier string in the replaced line vc98/include/
   String m_strrepdes; // string F:/program files/software/Microsoft Visual Studio 8/VC/include/
4. Required results:
5. "E:/program files/Microsoft Visual Studio/vc98/include/basetsd. H "/
6. Change to ==>
7. "F:/program files/software/Microsoft Visual Studio 8/VC/include/basetsd. H "/
9. The basetsd. H "/requirements remain unchanged.
10. */
12. Bool creplace: Deal ()
13. {
14. // Open the file
15. Cstdiofile hfile (m_strfilepath.c_str (), cfile: modereadwrite | cfile: sharedenywrite );
16. // Search
17. Cstring strtemp;
18. Cstring newstr;
19. Long iidx = 0;
20. While (hfile. readstring (strtemp ))
21. {
22. Iidx = strtemp. Find (m_strrepsrc.c_str (); // If the row contains an identifier string, replace
23. If (iidx! =-1)
24. {
25. // Obtain the replacement part;
26. NewStr = strTemp. Right (strTemp. GetLength ()-iIdx-1-m_strRepSrc.length (); // basetsd. h "/
27. // String to be replaced
28. NewStr = CString (_ T ("/" ") + CString (m_strRepDes.c_str () + newStr + CString (_ T ("/n "));
29. // Write back the file
31. HFile. Seek (-2-strTemp.GetLength (), CFile: current); // locate the start position of the string to be replaced
32. HFile. WriteString (newStr. GetBuffer ());
33. NewStr. ReleaseBuffer ();
35. }
36. }
37. HFile. Close ();
39. Return true;
40. }

Result 1 is not satisfactory because

"F:/Program Files/software/Microsoft Visual Studio 8/VC/include/basetsd. h"/length ratio

"E:/program files/microsoft visual studio/vc98/include/basetsd. h"/long

As a result, the content following "e:/program files/microsoft visual studio/vc98/include/basetsd. h"/in the file is overwritten.

Since

HFile. Seek (-2-strTemp.GetLength (), CFile: current );

HFile. WriteString (newStr. GetBuffer ());

Cause: hFile. ReadString is read back to the previous content, leading to an endless loop.

And the target file is increased several times (the previous content is written into)... Khan ====> I don't understand why the previous content is written into the file...

 

Conclusion: The content of a file cannot be directly replaced by a common method, unless it is the same as the length of the string to be replaced.

The same length can be achieved as follows

1. LPos = hFile. GetPosition ();
2. HFile. Seek (-2-strTemp.GetLength (), CFile: current );
3. HFile. WriteString (newStr. GetBuffer ());
4. Newstr. releasebuffer ();
5. Hfile. Seek (LPOS, cfile: Begin );

Finally, in another way, read the file content into the memory, replace the file content in the memory, and write it back to the file...

The implementation is as follows:

1. // Replace all strsrc in strbig with strdst
2. Void creplace: string_replace (string & strbig, const string & strsrc, const string & strdst)
3. {
4. String: size_type Pos = 0;
5. String: size_type srclen = strsrc. Size ();
6. String: size_type dstlen = strdst. Size ();
7. While (Pos = strbig. Find (strsrc, POS ))! = String: NPOs)
8. {
9. StrBig. replace (pos, srclen, strdst); // replace the srclen characters starting from the index pos with the strdst
10. Pos + = dstlen;
11. }
12. }
14. Bool CReplace: deal ()
15. {
16. Ifstream in (m_strFilePath.c_str ());
17. Stringstream ss;
18. Ss <in. rdbuf ();
19. String s = ss. str ();
21. // Size_type is of the unsigned type, which depends on the specific machine.
22. String: size_type iIdx = 0;
23. String: size_type iBegin, iEnd;
25. IIdx = s. find (m_strRepSrc );
26. If (iIdx! = String: npos)
27. {
28. IBegin = s. rfind ("/" ", iIdx );
29. IEnd = iIdx + m_strRepSrc.size ();
31. String sRep = s. substr (iBegin, iEnd-iBegin );
32. // S. replace (sRep, m_strRepDes );
33. String_replace (s, sRep, m_strRepDes );
35. // Write back
36. Ofstream out (m_strFilePath.c_str ());
37. Out <s;
38. // Out. close () is not required, and the out structure of the scope end will automatically close ()
39. }
41. In. close ();
43. Return true;
44. }