How to Search for a Piece of Text in Binary File by Using fstream - C/C++?
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Thread: How to Search for a Piece of Text in Binary File by Using fstream - C/C++?

  1. #1
    Join Date
    Sep 2008
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    119

    How to Search for a Piece of Text in Binary File by Using fstream - C/C++?

    I got a binary file, i opened the file. I need to look for this "255.255.255.255", and then replace it with the user newly inserted IP...

    I know there is something called seekp(), but it needs me to determine where to point in the file. I do not know yet. Once i find the spot 255.255... I will have to write from the iso::beg, right?

    1. I can go through the file line by line by using getline()...Is there another solution?

    2. Assume i went through the file & i found 255.255.255.255, to overwrite it do i t have to start from 2, or before 2? I guess ios::beg has to be involved in someway.

    3.
    Code:
    ofstream file1;
    file1.open("OutputTrial1.txt", ios::binary );
    file1.write(temp,sizeof(temp));
    file1.close();
    In this line file1.open("OutputTrial1.txt", ios::binary ); OutputTrial1.txt is not binary, so how come we specified it as a binary in parameter two?

    Regards

  2. #2
    Lindley is offline Elite Member Power Poster
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    Re: How to Search for a Piece of Text in Binary File by Using fstream - C/C++?

    Unless it's a really huge file, it's probably easiest to just read the entire file contents into a single string using getline() with EOF as the delimiter, then do the replace, then write the whole thing back out.

    If it *is* a really huge file, reading byte by byte until you find a '2' and then special-casing from there might be the easiest way. (At the furthest extent of this approach, you'd essentially have the DFA-based substring matching algorithm.)

  3. #3
    Join Date
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    Re: How to Search for a Piece of Text in Binary File by Using fstream - C/C++?

    Quote Originally Posted by Lindley View Post
    Unless it's a really huge file, it's probably easiest to just read the entire file contents into a single string using getline() with EOF as the delimiter, then do the replace, then write the whole thing back out.

    If it *is* a really huge file, reading byte by byte until you find a '2' and then special-casing from there might be the easiest way. (At the furthest extent of this approach, you'd essentially have the DFA-based substring matching algorithm.)
    The best may be a mixture of both of them. Read a fixed size chunk of data, replace the relevant occurences and read the next chunk. Thereīs a special case that must be handled when the text exceeds one chunk and is continued in the next one.

  4. #4
    Join Date
    Sep 2008
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    119

    Re: How to Search for a Piece of Text in Binary File by Using fstream - C/C++?

    1. Here is what i did! I do not know how good this piece of code is, it works %90 i need to fix it little bit, but the main disadvantage is i have to use Hex Workshop to get the offset of ip & offset of port then pass it manually to the parameter. I find it inefficient thats why i though to do it through fstream since its more flexible. I want to locate IP then overwrite it, same thing with port. Please look at the code & give suggestions if you don't mind

    Code:
    //get offsets through parameters and data to be inserted in place offset
    editBinary(long offsetOfIP, long offsetOfPortNumber, const char *IPAddress, const char *portNumber)
    {
        const DWORD MAX_NUMBER_OF_BYTES_IN_IP = 15;
        const DWORD MAX_NUMBER_OF_BYTES_IN_PORT = 5;
    
           DWORD numOfBytesWritten = 0;    
      
           HANDLE hFile = CreateFile(L"application.exe", GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
        
           if(hFile == INVALID_HANDLE_VALUE){
            cout<<"CreateFile() error: "<<GetLastError()<<endl;
            cout<<"*Make sure the file app.exe exists in the folder."<<endl;
            cout<<"Please press any key to go back"<<endl;
            cin.get();
            //get back
            }
    
           //point to IP offset
           DWORD successResult = SetFilePointer(hFile, offsetOfIP, NULL, FILE_CURRENT);
           if(successResult == INVALID_SET_FILE_POINTER)
           {
            cout<<"SetFilePointer() error: "<<GetLastError()<<endl;
            cout<<"Please press any key to go back"<<endl;
            cin.get();
            //get back
        }
      
           //overwrite the old IP - IPAddress contains the new IP
           BOOL numberOfIPBytesWrittenToFile = WriteFile(hFile, IPAddress, MAX_NUMBER_OF_BYTES_IN_IP, &numOfBytesWritten, NULL);
    
           if(numberOfIPBytesWrittenToFile == 0)
           {
            cout<<"WriteFile() error: "<<GetLastError()<<endl;
            cout<<"Please press any key to go back"<<endl;
            cin.get();
            //get back
            }
    
            //point to where port is located
        successResult = SetFilePointer(hFile, offsetOfPortNumber, NULL, FILE_BEGIN);
        if(successResult == INVALID_SET_FILE_POINTER)
        {
            cout<<"SetFilePointer() error: "<<GetLastError()<<endl;
            cout<<"Please press any key to go back"<<endl;
            cin.get();
            //get back
        }
    
            //overwrite the old port number - portNumber contains the new port number
        numOfBytesWritten = 0;  
            BOOL numberOfPortBytesWrittenToFile = WriteFile(hFile, portNumber, MAX_NUMBER_OF_BYTES_IN_PORT, &numOfBytesWritten, NULL);
    
         if(numberOfPortBytesWrittenToFile == 0)
         {
            cout<<"WriteFile() error: "<<GetLastError()<<endl;
            cout<<"Please press any key to go back"<<endl;
            cin.get();
            //get back
         }
    
            //close file
            BOOL isFileClosed = CloseHandle(hFile);
    
        if(isFileClosed == 0)
        {
            cout<<"CloseHandle() error: "<<GetLastError()<<endl;
            cout<<"Please press any key to go back"<<endl;
            cin.get();
            //get back
        }
    
            cout<<"Editing Succeeded."<<endl;
    }
    2.
    then do the replace, then write the whole thing back out.
    All data resides in the other file i just need to go through it. Once i find the spot i want to change, i start writing from there until data get fully replaced, then close the file. Can you clarify about why do i have to write the whole thing back out - this is right if i moved everything in a temp file afaik.Correct me if i'm wrong

    Ignore boundary checking for now...
    Last edited by f.ben.isaac; February 23rd, 2009 at 09:45 AM.

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