Function definition to count number of words

Question

Write a function definition that counts the number of words in a line from your text source.

I tried two different codes and got two different results

 countwords()
 {
    ifstream file("notes.txt");
    int count=0;
    char B[80];
    file>>B;
  While (!file.eof())
  {
   cout<<B<<endl;
   file>>B;  
   count++;
   }
}

This gives the desired answer.

The other way around :

 countwords()
 {
    ifstream file("notes.txt");
    char B[80];
    int count=0;
  While (!file.eof())
  {
   file>>B;
   cout<<B<<endl;
   count++;  
   }
}

But this gives an answer which is 1 more than the actual number of words.

Can someone please explain the working of the eof() function and the difference in these two loops?

Do NOT check on `eof()` Just search for why and you'll see. loop on `while(file >> B)` — AndyG, Jul 28 '15 at 13:55
I imagine the latter *may* also give a nice screen of gibberish, since `B` content is indeterminate and sending it to `cout` invokes UB. — WhozCraig, Jul 28 '15 at 13:59
Use a [`std::string`](http://en.cppreference.com/w/cpp/string/basic_string) instead of a `char[]` — NathanOliver, Jul 28 '15 at 13:59
[**Read this**](https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong). — WhozCraig, Jul 28 '15 at 14:00
There is no way any of that code gives any answers. Please post real code. — juanchopanza, Jul 28 '15 at 14:01

score 5 · Accepted Answer · edited May 23 '17 at 11:58

5

The second version of your answer will always loop one extra time.

Think about this: what happens if file >> B fails? You'll still increment count.

Also, do not loop on eof() because you'll typically loop one too many times. (Why is iostream::eof inside a loop condition considered wrong?)

Instead, do the following:

while(file >> B)
{
   std::cout << B << std::endl;
   ++count;
}

Because your filestream has an implicit conversion to bool that checks the state of it, and returns false if it's not good.

edited May 23 '17 at 11:58

Community

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answered Jul 28 '15 at 13:59

AndyG

39,700
8
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Well i have just started files in c++. so please dont mind if i say something wrong. But how can 'fil>>B' fail? As soon as it reaches the end, the 'eof()' would be true and the loop will terminate? – miyagi_do Jul 28 '15 at 14:16
@yasir: Waiting for `eof()` requires that you actually hit the end of file, but what if any of the other error conditions rear their head? File not existing, failed read, or any other `ios_base::failure`? `eof()` will continue returning `false` – AndyG Jul 28 '15 at 15:30

score 0 · Answer 2 · answered Jul 28 '15 at 14:01

0

The problem is not EOF however to see its working Read this.

Talking about your code, note the file>>B; in first code. Since file>>B; fails in last execution of second code, you get one less the correct answer.

answered Jul 28 '15 at 14:01

anshabhi

423
6
29

score 0 · Answer 3 · answered Jul 28 '15 at 14:04

The reason for outputting 1 more than the actual number of words: In the 2nd version you output B before reading it for the first time. This is a usage of an uninitialized variable and can result in outputting what will look like garbage, or an empty line. Unreliable code.

Also I would suggest using an std::string instead of char[80] as the type for your variable B.

Function definition to count number of words

3 Answers3