c++ fastest way to read only last line of text file?

Question

I would like to read only the last line of a text file (I\'m on UNIX, can use Boost). All the methods I know require scanning through the entire file to get the last line wh

Answer 1

I was also struggling on the problem because I ran uberwulu's code and also got blank line. Here is what I found. I am using the following .csv file as an example:

date       test1  test2
20140908       1      2
20140908      11     22
20140908     111    235

To understand the commands in the code, please notice the following locations and their corresponding chars. (Loc, char) : ... (63,'3') , (64,'5') , (65,-) , (66,'\n'), (EOF,-).

#include
#include
#include

using namespace std;

int main()
{
    std::string line;
    std::ifstream infile; 
    std::string filename = "C:/projects/MyC++Practice/Test/testInput.csv";
    infile.open(filename);

    if(infile.is_open())
    {
        char ch;
        infile.seekg(-1, std::ios::end);        // move to location 65 
        infile.get(ch);                         // get next char at loc 66
        if (ch == '\n')
        {
            infile.seekg(-2, std::ios::cur);    // move to loc 64 for get() to read loc 65 
            infile.seekg(-1, std::ios::cur);    // move to loc 63 to avoid reading loc 65
            infile.get(ch);                     // get the char at loc 64 ('5')
            while(ch != '\n')                   // read each char backward till the next '\n'
            {
                infile.seekg(-2, std::ios::cur);    
                infile.get(ch);
            }
            string lastLine;
            std::getline(infile,lastLine);
            cout << "The last line : " << lastLine << '\n';     
        }
        else
            throw std::exception("check .csv file format");
    }
    std::cin.get();
    return 0;
}