a lil' help using fread()

Can someone please help me with the usage of fread?

like errm, explain why my small test code don't quite work.

It's just reading a series of numbers(int) from a file.

Code:

int main(int argc, char **argv)
{
        FILE *fp;
        int *number = (int *)malloc(sizeof(int));
        int n;

        fp = fopen(argv[1], "r");

        while((n = fread(&number, sizeof(int *), 1, fp)) > 0);
                printf("n: %d -- %d\n", n, number);

        return 0;
}

many thanks!

Code:

while((n = fread(&number, sizeof(int *), 1, fp)) > 0);

Remove the red & sign - you already have a pointer, you don't want to write the number into your pointer, but into what your pointer points to (what you got back from malloc).

--
Mats

Code:

int main(int argc, char **argv)
{
        FILE *fp;
        int *number = malloc(sizeof(int));
        int n;

        fp = fopen(argv[1], "r");

        while((n = fread(number, sizeof(int *), 1, fp)) > 0);
                printf("n: %d -- %d\n", n, number);

        return 0;
}
~

this is the new version, but gcc kept complaining about the printf statement

Code:

read.c: In function ‘main’:
read.c:13: warning: format ‘%d’ expects type ‘int’, but argument 3 has type ‘int *’

and it didn't print out the write stuff in the file...

thx!

And what do you think that means? Perhaps you need a *number in your printf?

--
Mats

yea, i did that, but, somehow it still doesn't give the right output....

Code:

  printf("n: %d -- %d\n", n, *number);

is it due to me using 'vi' and typing numbers in a file rather than using fwrite() to write numbers to it....
that's why fread() doesn't seem to work right??

thx

Originally Posted by wuzzo87

yea, i did that, but, somehow it still doesn't give the right output....

Code:

  printf("n: %d -- %d\n", n, *number);

is it due to me using 'vi' and typing numbers in a file rather than using fwrite() to write numbers to it....
that's why fread() doesn't seem to work right??

thx

Well, it's probably showing exactly what you entered. Try this:
enter 1111, then see if the number you get is 825307441.

fread reads a binary format, not text-format, so your data content will not be (easily) typed in for example vi.

--
Mats

Hey thanks a lot for the help!!!!
certainly is useful

I got it to work already

> sizeof(int *)
If you're reading an int, use sizeof(int)

Originally Posted by Salem

> sizeof(int *)
If you're reading an int, use sizeof(int)

Good catch - it would work until you put it on a system that hasn't got the same size pointers as integers, such as a 64-bit OS. Subtle bug indeed.

--
Mats