Using fscanf to read a file one line at a time

[vcstarter]

This is straight C, not C++ or MFC. I want to know and how I can use fscanf and fputs to read a data file without determining the length. Here is what I am talking about.

My data file is in the form of

8.5
3.14
9.5
0.2
1.1

Now, it will be easier to do if I allow user to enter the length of the data, but I don't want that. I simply want user to enter the file name.

I would like to put fscanf inside a while loop and increment a counter for each line. After the end of the last line, I want to use malloc to allocate space for an array and put the value to that array. I want to know if it is possible and how I can do it.

[j0nas]

Sure you can do it.

But you should probably not use any scanf() function in any serious application!!!

If you know how to read in a float or double value from the keyboard, you should easily findout how to do it from a file.

Hint: %f or %lf

NOTE: scanf format codes work a bit different than printf's on floating-point numbers

[vcstarter]

I was think creating a dummy buffer to initialize like

float *x;

then allocate memory of 2 for it, then every time I read a new line, I realocate by the counter.

The problem is I have to read each and save it to a buffer or array.

[Andreas Masur]

[Moved thread]

[j0nas]

Yepp, you can reallocate space each iteration (but it may not be the best method)...

Use realloc()... something like this:

float *x = NULL;
int i = 0;

do {
    x = realloc(x, i + 1);
} while (fscanf(stdin, "%f", &x[i++]) == 1);
printf("Got %d rows of floats.\n", i);

[vcstarter]

Do you think of a better method rather than reallocate for each iterator?

[j0nas]

You have many options, like:
1. Precount rows in file, rewind the file and then allocate exact number of rows
2. Using a linked list
3. Allocate a fix number of array entries (with malloc) and let it grow if needed

I would probably go for number 3 in this case...

[vcstarter]

I understand number 3 and I probably go with it, but I like the idea of precount the number of row in the file. Do you know how can I do that inside a while loop? Is there any way you can show me how to do it with a snap code?

Thank you

[j0nas]

Method 1 requires a file (impossible on stdin)... so you basically do: (untested code)

for (rows = 0; fscanf(in, "%f", &f) == 1; rows++)
  ;
rewind(in);
x = malloc(rows * sizeof(float));
for (i = 0; i < rows; i++)
    fscanf(in, "%f", x + i);

Going through the file twice may or may not be a performance hit. If the file is still in the cache, it may not....

[vcstarter]

Thank you, this is the first time I see and heard the rewind function, I have never use it. By looking at its description from MSDN, it makes a lot of sense.

Base on what you said, I don't need while loop. The for loop should do it.