fread problems

Hello, I'm having problems with the fread function. I'm basically trying to read from a binary file. Here's my code :

Code:

---

//  diskp is a pointer to the file to be read
int read_blocks(int start_address, int nblocks, void *buffer)
{
        int f;
        int err_num;

        if ((fseek(diskp,start_address*BLOCK_SIZE,SEEK_SET)) != 0) // Seek to the point where read should start
        {
                fprintf(stderr,"Error in disk read : Unable to seek to given start location.\n");
                return 0;
        }

        if ((f = (fread(buffer,BLOCK_SIZE,nblocks,diskp))) != nblocks)  // Read from disk to buffer
        {
                if(feof(diskp) != 0)
                {
                        fprintf(stdout,"End of file reached. %d Blocks read.\n",f);
                        return 1;
                }

                if((err_num = ferror(diskp)) != 0)
                {
                        fprintf(stderr,"%s\n",strerror(err_num));
                }

                fprintf(stderr,"Error in disk read : Buffer write failed. %d\n",f);
                return 0;
        }
       
        return 1;
}

---

Ok. So everytime I run this. I get an error saying "Operation not permitted", and 0 blocks are read. At first my intuition said that maybe I didn't have read permission on the file I was working on, but an ls, latter showed that :

Code:

---

total 44
-rwxrwxrwx  1 ythiel  16268  200 Mar 14 12:24 disk  <--- file I am working on
-rwxr-xr-x  1 ythiel  16268  8136 Mar 14 12:24 disk_emu
-rw-------  1 ythiel  16268  3966 Mar 14 12:24 disk_emu.c
-rw-------  1 ythiel  16268  3968 Mar 14 12:23 disk_emu.c~
-rw-------  1 ythiel  16268  251 Mar 10 12:47 disk_emu.h
-rw-------  1 ythiel  16268  7323 Mar 10 12:47 disk_test.c
-rwx------  1 ythiel  16268  8256 Mar 13 17:45 diskemu
-rw-r--r--  1 ythiel  16268    0 Mar 14 12:36 dud

---

So I don't think that's the problem. Any ideas ?

> fread(buffer,BLOCK_SIZE,nblocks,diskp
Is your buffer really pointing at BLOCK_SIZE * nblocks bytes?

Normally, if you just want to read 'n' bytes, you just do
bytesRead = fread(buffer,1,nbytes,diskp);

I believe it is, here's how it's initialised :

Code:

---

data = (int*)calloc(1,(5*BLOCK_SIZE));

---

I then call my function using this :

Code:

---

read_blocks(10,5,data);

---

now the file I am working on is 80 bytes long, seperated into 20 blocks of 4 bytes (actually, sizeof(int) bytes), so even if those blocks are empty (which I don't think they are, anyways), I don't see how I would be getting an error.

Also, I actually do in fact have to seperate it into blocks of a certain given size. And although I can see how I could could just as well do this :

Code:

---

fread(buffer,1,BLOCK_SIZE*nblocks,diskp)

---

When I tried that, I got the same error.

Any other ideas ?

You'd have to post more code - like how some of those variables and constants are declared in main()

I take it diskp is a FILE* opened for reading binary data?

I feel so stupid. As it turns out, after discussing this with my TA this morning, I was opening my file with only write permission. Adding a little '+' to the whole thing solved the problem. Thank you for your time Salem.