FileIO in C++ problem.

TomCo

Hi, Im trying to read in from a file containing names and info (each on a seperate line) so I can create a linked list with the data.
I need to read in the name followed by the info but when I put two getline statements one after the other it crashes.

Any help would be much appreciated.

cout << "Please enter filename: ";
		string filename; 
		getline(cin,filename);

		ifstream myfile;
		myfile.open (filename.c_str());

		if (myfile.is_open())
		{
			node *temp, *temp2, *temp3; 

			while (! myfile.eof() )
			{

				getline(myfile,temp->name);
                                getline(myfile,temp->info);
				// do stuff with this line.
			}

			myfile.close();
		}
		else
			cout << "Unable to open file";

satchmo

You're creating pointers to node objects, but you're not creating any actual objects. When you write temp->name, you're dereferencing a pointer that doesn't point at anything, which is a Bad Thing.

TomCo

Ah, can't believe I didn't notice that!

I was convinced it had something to do with the getline statements, I always overlook the obvious.

Thanks.

TomCo

Crap, another problem cropped up.

cout << "Please enter filename: ";
		string filename; 
		getline(cin,filename);

		ifstream myfile;
		myfile.open (filename.c_str());

		if (myfile.is_open())
		{
			node *temp;

			temp = new node;
			while (!myfile.eof())
			{
				getline(myfile,temp->name);
				getline(myfile,temp->info);

				if (start_ptr == NULL)
				{ 
					start_ptr = temp;
					start_ptr->nxt = NULL;
				}

				cout << start_ptr->name;
				cout << start_ptr->info;
			}
				myfile.close();
		}
		else
			cout << "Unable to open file";

My input file is

a
a

b
b

c
c


Im just trying to get it to correctly create the start_ptr to being with.
start_ptr has a value of NULL initially and as far as I can see this code should only print "aaaaaa" but it prints "aabbcc".

If I put in the rest of my code to create the ordered list the whole thing goes into an infinite loop. It works fine without the file input.

satchmo

By saying start_ptr = temp, you're not assigning the value of temp to start_ptr, you're assigning the address. So saying start_ptr->name is the same as saying temp->name, which is why it's printing aabbcc.