Thread: Illegal seek error

Hey all,

Can anyone help me figure out why I'm getting the following error: "fseek in do_this:Illegal seek"?

Code:

void do_this(int file)
{
	char c;
	int disp = 0; //number of char read during this call
	int lines_read = 0; //number of lines read during this call
	if (lseek(file, pos, SEEK_SET) == -1);
	{
		int errNum = errno;
		display("lseek in do_this:");
		disp_err_msg(errNum);
	}
		while((pos <= file_size) && (pos > -1) && (lines_read <20))
		{
			if(read(file, &c, 1) == -1)
			{
				int errNum = errno;
				display("read in do_this:");
				disp_err_msg(errNum);
			}
			if (c == '\n')
			lines_read++;
			pos++;
			disp++;
			if(write(1, &c, 1) == -1)
			{
				int errNum = errno;
				display("write in do_this:");
				disp_err_msg(errNum);
			}
		}
}

Of course, pos is a global variable...

Thanks!

What is the value of pos, and how big is the file?

--
Mats

Well, 0 is not an invalid seek location, but if you get an error, then it's most likely because you are trying to seek to something that is non-zero, most likely the case is that you are trying to seek past the end of the file.

Print pos when you get the error, and which file it is for.

--
Mats

1. What number is "errno"? [ideally, I'd like to know the symbolic name, e.g. EINVAL, EBADFD or such].
2. Are you compiling the code with the correct header files, and does compiling with "-Wall" give you any warnings?

I think the error you are getting is this:

[EINVAL] Whence is not a proper value.

If the prototype for lseek() is not matched with the actual call, then "whence" is a random value on the stack [the second parameter offset is a 64-bit integer, and if you don't have the correct include file, the call would make it three 32-bit integers, causing the third "whence" parameter to be something other than the expected value, since two of the 32-bit values are "eaten" as the offset].

--
Mats

That is ESPIPE, which says that you are trying to do seek on a pipe. What does your code that calls "do_this" actually look like? Are you reading from a pipe or some such?

--
Mats

Well, the error code 29 means ESPIPE, which is said on lseek to be given when:

[ESPIPE] Fildes is associated with a pipe, socket, or FIFO.

http://www.hmug.org/man/2/lseek.php

Do you actually need to perform a seek at all - if you just opened the file, it should be at the beginning of the file [unless you opened it in append mode].

--
Mats

I have a feeling it "works" because your lseek isn't actually doing anything. Put a

Code:

if (pos != 0) printf("pos = %d\n", pos);

before your lseek, and see if that fires ever.

Edit: I perhaps should explain what I mean: If you have just opened a file, then the file would be at position zero, so if you try to lseek() unsuccessfully, to position zero, then you end up at position zero anyways. If you were to try to seek to another position, then it would be a different matter, and lseek() would make a difference.

--
Mats