C++ cant read file and append gives strange results

Question

I have a menu that that starts some methods based on user's choice. Two of the methods however don't work properly, and I have no idea why. This is the part of the menu for them:

case 2:
{
    string fileName;
    cout << "Which file to read?:";
    cin>>fileName;
    this->ReadFromFile(fileName);
    break;
}
case 3:
{
    string fileName;
    cout << "Enter name for the file:";
    cin>>fileName;
    this->WriteToFile(fileName);
    break;
}

Here are the methods:

void ReadFromFile(string file)
    {
        string line;
        ifstream rfile ("FileSystem/" + file);//open file for reading
        if (rfile.is_open())
        {
            while(getline(rfile, line))
            {
                cout << line << endl;
            }
        }
        else
        {
            cout << "An error occurred when tried to read from this file." << endl;
        }
        rfile.close();
        _getch();
    }

    void WriteToFile(string fileName)
    {
        ofstream myFile;
        ifstream exists (fileName);//open read stream to check if file exists
        if(exists)//returns true if file can be opened and false if it cant
        {
            exists.close();//close the stream
            myFile.open(fileName, ios_base::app);// open file for reading(ostream)
        }
        else
        {
            exists.close();
            CreateFile(fileName);//file doenst exists, so we create one and list it in the file tree
            myFile.open("FileSystem/" + fileName, ios_base::app);// open file for reading(ostream)
        }
        if(myFile.is_open())
        {
            string input;
            cout << "start writing and press enter to finish. It will be done better later." << endl;
            cin>>input;
            myFile << input;

        }
        else
        {
            cout<<"An error occurred when tried to open this file."<<endl;
        }
        myFile.close();
        _getch();
    }

Now here is the funny part. When I try to write something to a file, it doesn't matter that I open it with: 'ios_base::app' or 'ios:app' it just rewrites it. But it cant even do that properly. If i have a line with whitespaces like'Hi this is me.' for example, it only writes the first word, which here is 'Hi'. So if I then decide to read the file the first thing that happens is that it says that the file cant be oppened, even before it asks me for a name. That happens the first 3 tries and then the reading magically works. I have bashed my head into this for the last two hours and I still cant understand what is happening. Can anyone please explain this to me, and show me my mistakes?

Narrow, narrow, narrow! Use a debugger first! – πάντα ῥεῖ Jun 07 '14 at 19:46 — πάντα ῥεῖ, Jun 07 '14 at 19:46

score 0 · Accepted Answer · edited May 23 '17 at 12:27

0

string input;
cout << "start writing and press enter to finish. It will be done better later." << endl;
cin>>input;
myFile << input;

In the lines above, cin>>input will stop reading at a space. You should use std::getline instead. See also this answer.

edited May 23 '17 at 12:27

Community

1
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answered Jun 07 '14 at 19:48

wimh

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When i use std::getline(std::cin,input) it stops after the first key ive pressed. It doesnt write anything, and also it deletes everthing in the file. – Radostin Angelov Jun 07 '14 at 19:59
Your previous read action (`cin>>fileName;`) does not 'eat' the newline. So getline reads just the newline you entered after the filename. See [How do I flush the cin buffer?](http://stackoverflow.com/q/257091/33499) – wimh Jun 07 '14 at 20:23
Thanks, that fixed it. Other than that i found that the way I tried to find if the file can be oppened for some reason allways returned false. Anyway i fixed that too. – Radostin Angelov Jun 07 '14 at 20:48

C++ cant read file and append gives strange results

1 Answers1