Subclass unable to access member function

[Acr]

Good day,

I've been setting up my datastructure as such: I have one class 'Storage' and a subclass 'StorageMap'.

The header files of both (constructors and non-relevant stuff removed):

Storage.h

class Storage {

public:
	virtual void loadFile();

protected:
	char* filename;
	std::ifstream file;
};

StorageMap.h

#include "Storage.h"

class StorageMap : public Storage {

	public:
		void loadFile();

	private:
};

What I try to do is that StorageMap is a subclass of Storage. This seems to be the case. Now, I have a protected variable 'std::ifstream file;' in Storage, which StorageMap should also be able to access (right?).

I try to open the file using it's filename (which works I think) and then read it line-by-line using 'while end of file not reached' but I can't use 'while (!file.eof)': error C2276: '!' : illegal operation on bound member function expression

The CPP code:

Storage.cpp

#include "Storage.h"
//Removed constructor etc..

void Storage::loadFile() {
		printf("Error: No calling loadfile on generic storage object");
		exit(1);
}

StorageMap.cpp

#include "StorageMap.h"

//Removed constructor etc..

void StorageMap::loadFile() {
	file.open(filename, std::ios::in );
	if (!file.is_open()) {
		printf("Error opening or finding file with filename '%s'.", filename);
		exit(1);
	}

	std::string line;
	while(!file.eof) {   //<<<<<<---BREAKS HERE
	        getline(file,line); // Save the line.
	        printf("%s\n", line);
    }
	
	file.close();
}

Am I doing something horribly wrong here? Since StorageMap is a subclass of Storage, it also has a 'file' variable it can use (right?). Why exactly doesn't this work?

Kind regards

[LBEaston]

eof is a function. try (!file.eof()) instead of (!file.eof)

[Acr]

Thanks, that fixed it. I was so caught up searching for the strange error message and figuring out if I had accidentally messed up a pointer that this obvious flaw went unnoticed. Thanks.

[sohguanh]

If I remember correctly, eof() has a subtle bug I believe. Try to use while (getline(file,line)) { ... } instead.

That developer spent endless nights debugging this stuff :P

[Acr]

Will take your advice and go with your suggestion. Thanks :)

[simondeeley]

Maybe poking my nose in unnecessarily here, but you can avoid having that implementation of Storage::loadFile() by declaring the function to be pure virtual:

class Storage {

public:
	virtual void loadFile() = 0;

The compiler will then
- require that all derived classes implement the function and
- not allow a 'Storage' object to even be instantiated

If this is what you intended, it's a great way to get the compiler to check that your classes are being used correctly.

[Acr]

Maybe poking my nose in unnecessarily here
By all means, poke around!

Thanks for the suggestion, I can certainly use this! I currently had a small loadFile function that said "Please use a derived class instead" and have it quit the application. This is much nicer.