tail.cpp

#include <fstream>
#include <vector>
#include <string>

#define BUF_SIZE 512

/* Save the last 'n_lines' lines of 'filename' into vector 'dest'.
 * ignore_last_line is useful for \n-terminated files.
 * Function returns number of written lines or -1 on error.
 */
int tail(std::string filename, int n_lines, std::vector<std::string> *dest, bool ignore_last_line)
{
	int length = ignore_last_line ? (n_lines + 1) : n_lines;
	int count = 0;
	char buf[length][BUF_SIZE];

	std::ifstream fin;
	fin.open(filename.c_str(), std::ifstream::in);
	if(!fin.good())
		return -1;
	
	while(!fin.eof()) {
		fin.getline(buf[count % length], BUF_SIZE);
	/*	
		if(fin.fail() && !fin.eof()) {
			// fin.fail() is set if either the current bufs is longer than BUF_SIZE-1 characters
			// or if an EOF mark is found before another newline. The latter is responsible for the blank 
			// line at the end of the output. Try ignore_last_line = true.
		}
        */
		count++;
	}
	fin.close();

	int start = (count < length) ? 0 : count;
	int stop = (count < length) ? count : (count + length);
	if(ignore_last_line) stop--;
	
	for(int i = start; i < stop; i++) 
		dest->push_back(buf[i % (length)]);


	return ((count < n_lines) ? (ignore_last_line ? (count - 1) : count) : n_lines);
}