CODEWITHSUNDEEP
c++
OpalG
OpalG

Reputation: 23

How to move from the end of the file to the beginning in c++

Im having a small problem with my code. I have been trying to read some information from the end of a random access file then repositioning the cursor at the beginning of the file. So far seekg has not been working. Here is my code:

void main ()
{
    AssignData FileOut;
    AssignData FileIn;

    ofstream OutData("Data.dat", ios::out | ios::app | ios::binary);
    ifstream InData("Data.dat", ios::in);

    cout <<"Writing to file" << endl;

    if (!OutData)
    {
         cout<<"File does not exist"<<endl;
     exit(1);
    }

    //read through file

    while (InData.read( reinterpret_cast< char * >( &FileIn ),sizeof( AssignData ) ))
    {                        
    }

    FileIn.DisplayFileContent();//displays the last line in the file

    FileOut.setInfo();//allows user to add another record

    //Writes record to file
    OutData.write( reinterpret_cast< const char * >( &FileOut ), sizeof(AssignData) );                                        

    OutData.close();
    cout << endl<<endl;
    //Reads the first record from the file

    InData.seekg(0);

    while (InData.read( reinterpret_cast< char * >( &FileIn), sizeof(AssignData) ))
    {
    // display record
        if ( (FileIn.getID() != 0) || (FileIn.getID()!=NULL) )
    {
        FileIn.DisplayFileContent();
    }                         
    }

    InData.close();

    _getch();
    exit(0);
}

Upvotes: 2

Views: 9755

Answers (2)

Konrad
Konrad

Reputation: 41017

To go to the end of the file:

ifstream is;
is.open( "file.txt", ios::binary );
is.seekg (0, ios::end);

To get the length of the file (when at the end), use tellg which returns the absolute position of the get pointer.

length = is.tellg();

To go back to the beginning use seekg again, this sets the position of the put pointer.

is.seekg (0, ios::beg);

If you have tried this could you be more specific about what isn't working?

Upvotes: 6

paulsm4
paulsm4

Reputation: 121849

You probably want "seekg(ios_base::beg)":

http://bytes.com/topic/c/answers/602553-ifstream-seeking

http://www.cplusplus.com/reference/iostream/istream/seekg/

If it's "not working", two things to try:

1) check position "tellg()"

2) check error status (eofbit, failbit, badbit)

Upvotes: 0

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