counting the number of lines in a text file

Question

I m reading lines off of text file and I m wondering if this is a good way to go  I had to write the function numberoflines to decrease the number of lines variable by one because within the while loop  for every line it read it adds 2 to the number of lines variable    include  lt iostream gt   include  lt fstream gt  using namespace std   int number of lines   0   void numberoflines    int main        string line      ifstream myfile  textexample txt         if myfile is open             while  myfile eof                 getline myfile line               cout lt  lt  line  lt  lt  endl              number of lines                      myfile close              numberoflines        void numberoflines        number of lines--      cout lt  lt  number of lines in text file     lt  lt  number of lines  lt  lt  endl      Is there any other easier better way

User · Accepted Answer

Your hack of decrementing the count at the end is exactly that -- a hack.

Far better to write your loop correctly in the first place, so it doesn't count the last line twice.

int main() { 
    int number_of_lines = 0;
    std::string line;
    std::ifstream myfile("textexample.txt");

    while (std::getline(myfile, line))
        ++number_of_lines;
    std::cout << "Number of lines in text file: " << number_of_lines;
    return 0;
}

Personally, I think in this case, C-style code is perfectly acceptable:

int main() {
    unsigned int number_of_lines = 0;
    FILE *infile = fopen("textexample.txt", "r");
    int ch;

    while (EOF != (ch=getc(infile)))
        if ('\n' == ch)
            ++number_of_lines;
    printf("%u\n", number_of_lines);
    return 0;
}

Edit: Of course, C++ will also let you do something a bit similar:

int main() {
    std::ifstream myfile("textexample.txt");

    // new lines will be skipped unless we stop it from happening:    
    myfile.unsetf(std::ios_base::skipws);

    // count the newlines with an algorithm specialized for counting:
    unsigned line_count = std::count(
        std::istream_iterator<char>(myfile),
        std::istream_iterator<char>(), 
        '\n');

    std::cout << "Lines: " << line_count << "\n";
    return 0;
}

User · Answer

I think your question is   why am I getting one more line than there is in the file    Imagine a file   line 1 line 2 line 3   The file may be represented in ASCII like this   line 1 nline 2 nline 3 n    Where  n is byte 0x10    Now let s see what happens before and after each getline call   Before 1  line 1 nline 2 nline 3 n   Stream    After 1   line 1 nline 2 nline 3 n   Stream             Before 2  line 1 nline 2 nline 3 n   Stream            After 2   line 1 nline 2 nline 3 n   Stream                     Before 2  line 1 nline 2 nline 3 n   Stream                    After 2   line 1 nline 2 nline 3 n   Stream                              Now  you d think the stream would mark eof to indicate the end of the file  right   Nope   This is because getline sets eof if the end-of-file marker is reached  during it s operation    Because getline terminates when it reaches  n  the end-of-file marker isn t read  and eof isn t flagged   Thus  myfile eof   returns false  and the loop goes through another iteration   Before 3  line 1 nline 2 nline 3 n   Stream                            After 3   line 1 nline 2 nline 3 n   Stream                            EOF   How do you fix this   Instead of checking for eof    see if  peek   returns EOF   while myfile peek      EOF       getline       You can also check the return value of getline  implicitly casting to bool    while getline myfile line        cout lt  lt

User · Answer

In C if you implement count line it will never fail  Yes you can get one extra line if there is stray  ENTER KEY  generally at the end of the file   File might look some thing like this    hello 1  Hello 2      Code below   include  lt stdio h gt   include  lt stdlib h gt   define FILE NAME  file1 txt   int main          FILE  fd   NULL      int cnt  ch       fd   fopen FILE NAME  r        if  fd    NULL                perror FILE NAME               exit -1              while EOF     ch   fgetc fd                    int fgetc FILE    returns unsigned char cast to int        Because it has to return EOF or error also                      if  ch      n                         cnt             printf  cnt line in  s is  d n   FILE NAME  cnt        fclose fd       return 0

User · Answer

with for-loop   std  ifstream myFile  std  string line  int lines   myFile open path    for lines   0  std  getline myFile line   lines      std  cout  lt  lt  lines  lt  lt  std  endl

[c++] counting the number of lines in a text file

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