fstream questions!

This is a discussion on fstream questions! within the C++ Programming forums, part of the General Programming Boards category; So in the constructor for my class, i want it to check to see if the list file is there ...

  1. #1
    Registered User Terran's Avatar
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    fstream questions!

    So in the constructor for my class, i want it to check to see if the list file is there list.bin if so i want it to open it, else wise, i'd like it to create it. I also want it to ignore it if it's empty, but it doesn't seems to work.

    Code:
        std::ifstream fin("list.bin", ios::binary); //open it to read? Can this also create it?
        if (!fin){ // if it doesn't exist? this works.
            wxMessageBox("File Function Failed!"); 
        }
        else {  // if it exists...
            if(!fin.eof()){ // .. but what if it's empty?
                wxMessageBox("NOT EMPTY!"); // this happens with a seemingly empty file!
                
            }
            else {
                wxMessageBox(" EMPTY!"); 
                fin.close(); // this is in the wrong place, ignore it!
            }
        }
    Last edited by Terran; 07-04-2008 at 05:47 PM.
    Sorry, but i'm a Code::Blocks man now.

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    There's no point in opening a file for reading and creating it if it doesn't exist, so the ifstream doesn't do that. I'd check to see if the file opened. If it didn't then create with an ofstream. If it did, read it.

    As far as your problem with eof(), it will never return true with a new file stream until after you've attempted to read. You have to do some read operation first, and that read operation has to attempt to read when there are no more characters, then eof() will be true.

  3. #3
    Registered User Terran's Avatar
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    Quote Originally Posted by Daved View Post
    There's no point in opening a file for reading and creating it if it doesn't exist, so the ifstream doesn't do that. I'd check to see if the file opened. If it didn't then create with an ofstream. If it did, read it.

    As far as your problem with eof(), it will never return true with a new file stream until after you've attempted to read. You have to do some read operation first, and that read operation has to attempt to read when there are no more characters, then eof() will be true.
    Ahh then that's ok, cause i was thinking i'd get an error if tried to read from a non-existent file. So really i can just try to read the data and it's no big deal if it doesn't read it.
    Sorry, but i'm a Code::Blocks man now.

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