Thread: Filestream Not Seeking to the Beginning

Can someone please explain to me what I'm doing wrong. The output is clearly wrong. The first value in the array is 73, therefore I don't think it's seeking to the beginning of the file properly, which would explain why the rest of the values are -1.

The file just contains 10 words on separate lines of various lengths.

Code:

int Process_File(arguments file_args) {
 
	ifstream fd(file_args.file, ios::in); // file_args.file = file path
 
	if (!fd) {
		printf("File open error.\n");
		return 0;
	}
 
	char tmp[50];
	int lines;
 
	while (fd) {	
		fd.getline(tmp, 50);
 
		if (fd)
			lines++;
	}
 
	printf("There are: %d lines.\n", lines);
 
	int * offsets = new int[lines];
 
	fd.seekg(0, ios_base::beg);
 
// Supposed to store the character positions of each new line in an array
// Array index represents the line number, value represents character position
 
	for (int i = 0; i <= lines; i++) {
		offsets[i] = fd.tellg();
		fd.getline(tmp, 50);
	}
 
	for (int i = 0; i <= lines; i++)
		printf("line: %d, character: %d\n", i, offsets[i]);
 
	return 0;
}

Code:

Output:
 
There are: 10 lines.
line: 0, character: 73
line: 1, character: -1
line: 2, character: -1
line: 3, character: -1
line: 4, character: -1
line: 5, character: -1
line: 6, character: -1
line: 7, character: -1
line: 8, character: -1
line: 9, character: -1
line: 10, character: -1

Update: Ok so I thought I'd give it a shot with a vector instead... But now the problem is with printing the 5th line (as a test to see if it's working properly). The math seems fine, I can count in the file and see that the numbers are correct, but it isn't printing the 5th line, it's just printing nothing...

This leads me to believe it's a problem with seekg(), and instead of it seeking to word[4] it's not working, so it's reading nothing (from past the end of the vector).

So I must be doing something wrong with tellg and seekg... I can't get either of them to do what they're supposed to do (unless it turns out that those aren't the real problem and I'm missing the real problem).

Code:

int Process_File(arguments file_args) {
 
		ifstream fd(file_args.file, ios::in);
 
	if (!fd) {
		printf("File open error.\n");
		return 0;
	}
 
	char tmp[50];
	int lines = 0;
 
	vector<int> words;
 
	while (fd) {		
		words.push_back(fd.tellg());
		fd.getline(tmp, 50);
 
		if (fd)
			lines++;
	}
 
	printf("There are: %d lines.\n", lines);
 
	for (unsigned int i = 0; i < words.size(); i++)
		printf("line: %d, character: %d\n", i, words[i]);
 
	fd.seekg(words[4]);
	fd.read(tmp, words[5] - words[4]);
 
	printf("(pos: %d len: %d) Line 5 contains: %s\n", words[4], words[5] - words[4], tmp);
 
        return 0;
}

Here's the output. I chopped off a lot of the results because it's quite large:

Code:

There are: 73 lines.
line: 0, character: 0
line: 1, character: 7
line: 2, character: 14
line: 3, character: 20
line: 4, character: 30
line: 5, character: 36
line: 6, character: 51
line: 7, character: 57
line: 8, character: 62
line: 9, character: 73
(pos: 30 len: 6) Line 5 contains:

You first use the stream to read the file to the end, which sets the eof bit. You'll need to clear() that error condition before you can use the stream again.