Reading from file using fgets

Question

I am reading from file of format

1 32 43 23
32 43
123 43 54 243 
123 2222
2

Here is my code snippet.

string[100];
while(!feof(fp))
    fgets(string,100,fp)

Now, when I put every string, in the last string I am getting repetition and some more ambiguities (like something else also gets printed say 123 or so).

How to solve this problem?

Ransom

Is there an end-of-line \n character at the end of the last line in your file? – Hardenberg

Post your full actual code, this shouldn't even compile. – Sarge

Answer 1

You need to check the return value of fgets. If a read has been successful, fgets returns the pointer to the buffer that you passed to it (i.e. string in your example). If the End-of-File is encountered and no characters have been read, fgets returns NULL.

Try this:

char string[100];
while(fgets(string, 100, fp)) {
    printf("%s\n", string);
}

Hardenberg

Why would you test with feof if fgets does so? – Capstan

@ManuelReis You are right, feof test s unnecessary (edited). – Hardenberg

Thanks for the answer, I was having an existential crisis for a second. – Capstan

The \n inside issued by the printf is not necessary, as it already comes via fgets() from inside the file (if around). – Dyspnea

Having fgets() return value assumed to be 0, this code works. Generally NULL is not necessarily 0, it is generally (void*)0. Code is more readable, if you check with NULL – Brag

Answer 2

The eof is only reached after you have attempted to read from a file that is at the end. You have to use the return value of fgets instead (which returns NULL on eof or error and the pointer it is given otherwise):

char string[100];
while(fgets(string, 100, fp))
    // do stuff with string

Checking the return value like this will cause you never to hit the eof inside the body of the loop, like the other one, instead of in the condition.

Mcguigan