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 <iostream> #include <fstream> 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<< line << endl;             number_of_lines++;         }         myfile.close();     }     numberoflines();  }  void numberoflines(){     number_of_lines--;     cout<<"number of lines in text file: " << number_of_lines << endl; } 

Is there any other easier better way?

Answer 1

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; } 

Answer 2

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<< ...