Binary File I/O Issues

[darkcammo]

Hello! I'm having some issues with binary file I/O. I've never used it before and I'm having some trouble. I've got a cpp file with my main function, then I've got a class I've made tsuPod.cpp and the header for it tsuPod.h

For some reason, my binary input/output file is not being created or written to, and I'm not sure why. I listed the fstream as a private member of the tsuPod class and I'm opening the file in the constructor when it is called from main. I think this is the problem, but I'm not sure why. Thank you in advance for help!

Call from main:

tsuPod tpod(memory, capacity);

from tsuPod.h

class tsuPod
{
	private:
		int max_memory;
		int song_capacity;
		int remaining_memory;
		int total_songs;
		fstream memory;
	public:
		tsuPod(int, int);
		void showSongList();
		int addSong ();
		int removeSong ();
		void clearMemory();
		void shuffle ();
		void sortSongList();
		void statusCheck (int);
		int getTotalMemory() const
			{ return max_memory; }
		int getRemainingMemory() const
			{ return remaining_memory; }
};

from tsuPod.cpp

tsuPod::tsuPod (int max_mem, int song_cap)
{
	max_memory = max_mem;
	remaining_memory = max_mem;
	song_capacity = song_cap;
	total_songs = 0;
	memory.open("tsupod_memory.dat", ios::in | ios::out | ios::binary);

	memory.write("Howdy", 0);

	return;
}

[nvrmnd]

memory.write("Howdy", 0 );

[darkcammo]

Of course I appreciate the help, but if I coded something, it was because I thought that it was right. Restating something I coded with no explanation doesn't exactly help, but I appreciate you pointing out where you think the error could have occurred.

I thought the int parameter of the write() method was the location of where to start writing in the file. I chose 0, for the beginning of the file. For grins I also tried 100 and still no luck.

Any more ideas?

[Chervil]

You could look at the documentation for the write() function. Understanding what each parameter is used for, and how the function is intended to work will be useful.
http://www.cplusplus.com/reference/ostream/ostream/write/

[darkcammo]

That was very helpful thank you! However, I've tracked the problem down even further. Now that I've got a proper function call the file is STILL not being created. Perhaps I'm going crazy?

fstream mem1;
mem1.open("tsupod_memory.dat", ios::in | ios::out | ios::binary);
if (mem1)
	cout << "open!";
char test = 'o';
mem1.write(&test, sizeof(test));

I'm not even getting the cout << "open!";

[Daleth]

It is because of your open mode. It includes ios::in, so the program will not create the file if it does not yet exist.

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

int main()
{
                  //Uncomment the section below to see the difference
    fstream file("data.dat", /*ios_base::in | */ios_base::out | ios_base::binary);
    if(!file.is_open())
        cout << "Unable to open.";
    else{
            //Reopen because the standard I/O library does not allow you to
            //    change the openmode without opening a file
        file.close();
        file.open("data.dat", ios_base::in | ios_base::out | ios_base::binary);
        string s("Hello world!");
        file.write(s.c_str(), s.size());
        char buf[100] = {'\0'};
        file.seekg(0);
        file.read(buf, 100);
        cout << buf;
    }

    return 0;
}

[darkcammo]

Suddenly, it all makes sense. Thank you!

So I should be able to open it for output only to create it, then close it, then open it for input AND output.

About to go test, thank you again!

[darkcammo]

Worked, as expected. Thank you again.