accessing fstream open arguments

[mzimmers]

Hi -

I'd like to write a utility routine to open files. One of the arguments to the routine would be the io mode (read, write, etc.) How does one access these arguments and store them in a variable?

This is what I'd like to do:

some_variable_type mode;
mode = ios::out | ios:: ate;
rc = openFile (fileName, mode, fp);

Thanks...

[ciphermagi]

My immediate instinct would be to simply create your own determinant, and then make an if-else statement to decide which mode you're going to use.

[mzimmers]

Yeah, I can do that easily enough; I was just wondering whether there was a more direct route. But, that's fine. Thanks.

[ciphermagi]

I know there are languages out there that can use and modify their own commands and variable names, but I don't think that C++ is one of them.

[mzimmers]

I'm not really trying to modify anything; just access them somehow. For example, I know that ios::out is a 0x10, but I don't know how to "grab" that value and pass it as a parameter (or even use it in a variable as I described above). It doesn't make sense that C++ would keep that hidden from the user, does it?

[ciphermagi]

Well, what you're really asking to do is to pass a non-variable command type argument to a function, which I don't think I've ever seen done. In order for you to be able to do that, C++ as a language would have to be aware of itself, which it isn't.

[ne555]

¿ std::ios_base::openmode ?
¿Or do you want to implement something like http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.20 ?

[mzimmers]

ne555: that's exactly what I wanted. My routine now looks like this:

template <class T> void	openFile(string& name,
			 T& file,
			 const	int	ioMode)		// 0 = read; 1 = write
{
	std::ios_base::openmode ioFlags;

	if (ioMode == FILE_READ)
		ioFlags = ios_base::in;
	else
		ioFlags = ios_base::out;

	file.setf(ios::hex, ios::basefield);
	file.open(name.c_str(), ioFlags);
	if (!file.good())
	{
		cout << "Demod: error opening " << name << "." << endl;
	}
}

This seems to work fine; thanks for the help.

[Stewbond]

How about:
#define mode (ios::out | ios:: ate)

[mzimmers]

Hi, Stewbond - the program I'm running should scrap all old output and regenerate the files, so the ate bit isn't appropriate here. I'll keep it in mind for future applications, though.