Using sscanf to grab an unknown number of variables

R00ts · 06-06-2005, 04:08 PM

I have files containing floating point data that is tab-delimted. I need to read in these files to fill a 2 dimensional vector. The problem here is that I don't know how many floating point data there are per-line in the file (however the number of entries are consistent within the file). So I wanted to use getline to grab each new line of data and then use sscanf to parse the data, but I'm stuck on how to do this. Here's what I've got written so far.

Code:

// >>>>> (1) Try to open the input file for reading
	ifstream fin(input_filename.c_str());
	if(!fin) {
		cerr << "ERROR: Problem opening file " << input_filename << " for reading." << endl;
		fin.close();
		exit(1);
	}

	// >>>>> (2) Read in the first line and determine how many PMC data entries
	// >>>>>     are in the file
	char ch;
	int pmc_entries = 0;
	do {
		fin.get(ch);
		if (fin.bad()) {
			cerr << "ERROR: Problem reading file " << input_filename << endl;
			fin.close();
			exit(1);
		}

		if (ch == '\t' || ch == '\n') {
			pmc_entries++;
		}
	} while (ch != '\n');

	cout << "File has " << pmc_entries << " pmc entries" << endl;
	vector<vector<float> > pmc_data(pmc_entries);

	// >>>>> (3) Return to the beginning of the file and read in each line of
	// >>>>>     data into the pmc_data vector <<<<<
	int i = 0;
	int v = 0;    // A  << counter for the pmc_data vector element to fill
	char line[1000];

	fin.seekg(0); // Go back to the beginning of the file

	while (fin.good()) {
		fin.getline(line, 1000);
		for (i = 0; i < pmc_entries; i++) {
			sscanf(line,"%f\t",&pmc_data[v][i]);
		}
	}

The problem is with the sscanf line inside the inner for loop. It will continually read the same floating point number (the first one in the file) every loop. It would be simple enough for me to construct a string that consisted of multiple "%f\t" for the exact number of entries, but how can I specify where each of those values go (in the pmc_data[][] vector)? Could I use the elipse (...) operator to somehow fill the first dimension of that vector?

Thanks for any ideas you may have

jim mcnamara · 06-06-2005, 04:34 PM

Read the first line, count the tabs. That gives you the number of fields for every line.

R00ts · 06-06-2005, 04:49 PM

Quote:

Originally posted by jim mcnamara
Read the first line, count the tabs. That gives you the number of fields for every line.

I already do that in the code I posted above. That's not the problem. The problem is how to use sscanf to read in an arbitrary number of floating point values that aren't known until run-time.

jim mcnamara · 06-06-2005, 04:55 PM

You can't. You'll have to use varargs.h to call a routine that accepts the number of items then branches to a sscanf call with the right number of arguments.

It would be easier to read and maintain if you just copied each substring (ending in a tab) to a temp string, then called sscanf for a single value

R00ts · 06-06-2005, 05:03 PM

That's what I thought, ok thanks. I'll go with your substring split idea.