Right, the kernel didn't change anything. It was a pointer mistake. This line from the tutorial didn't work:
and it worked with :
This is pointer arithmetic, which always adds in multiples of the base type. So "ptr + 3" amounts to "position_in_bytes + sizeof(type_of_pointer)*3"
So it's the difference between adding "sizeof(struct ip)*sizeof(whatever_type_datagram_iis)" bytes and adding "sizeof(struct ip)*sizeof(struct tcphdr)" bytes.
Hi everybody!!
I'm studding at the university raw sockets, but i can't find a good place to read about them...
Does anybody now where i can find some information???
I've been goggling a lot but couldn't find nothing useful, just man pages...
by the way, I'm programming under Linux...
Bye! (4 Replies)
Ok, so I'm trying to finalize my understanding of read/write and kernel interaction.
read():
You have a library function that has as it's first parameter (what the open file to read from is), second parameter( a pointer to a buffer (is this the location of a buffer in the user area or the... (1 Reply)
Ok, so I'm trying to finalize my understanding of read/write and kernel interaction.
read():
You have a library function that has as it's first parameter (what the open file to read from is), second parameter( a pointer to a buffer (is this the location of a buffer in the user area or the... (7 Replies)
We have a server-client communication in our application. Sockets are used for the communication. We are using AF_INET sockets with SOCK_STREAM(TCP/IP). Also these sockets are in Non Blocking mode (O_NONBLOCK). Application is written in C++ on UNIX.
In our system the Server will write to a... (4 Replies)
I am trying to make a server and client, the client will choose between some options and the server will react accordingly.
After a some reads and writes that work the server needs to read from client an INT i use this:
read(newSd,&k,sizeof(int));But even if all the other times there was no... (1 Reply)
I'm a beginner to the Linux programming and trying my hands on some device driver examples while practising. The below code (a trimmed down version of tiny_tty.c from ldd3 book) loads perfectly using insmod and I'm able to see it in /proc/tty/drivers , /proc/modules and device nodes are getting... (1 Reply)
I'm trying to lookup the definition of the ext4 superblock schedule in the kernel header files, but I can't seem to locate the files. I'm running the most recent Raspian Debian Wheezy OS with kernel version 3.18. Any help is greatly appreciated. Thank you!! (1 Reply)
Hi,
Its been a long time since i programmed a multithreaded application that can do Tx and Rx of datagrams over unix sockets.
I well remember that though the threads were efficiently designed to be independent of each other, and was writing to different sockets, there was a limitation ,... (0 Replies)
Discussion started by: binnyjeshan
0 Replies
LEARN ABOUT V7
offsetof
OFFSETOF(3) Linux Programmer's Manual OFFSETOF(3)NAME
offsetof - offset of a structure member
SYNOPSIS
#include <stddef.h>
size_t offsetof(type, member);
DESCRIPTION
The macro offsetof() returns the offset of the field member from the start of the structure type.
This macro is useful because the sizes of the fields that compose a structure can vary across implementations, and compilers may insert
different numbers of padding bytes between fields. Consequently, an element's offset is not necessarily given by the sum of the sizes of
the previous elements.
A compiler error will result if member is not aligned to a byte boundary (i.e., it is a bit field).
RETURN VALUE
offsetof() returns the offset of the given member within the given type, in units of bytes.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99.
EXAMPLE
On a Linux/i386 system, when compiled using the default gcc(1) options, the program below produces the following output:
$ ./a.out
offsets: i=0; c=4; d=8 a=16
sizeof(struct s)=16
Program source
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
struct s {
int i;
char c;
double d;
char a[];
};
/* Output is compiler dependent */
printf("offsets: i=%zd; c=%zd; d=%zd a=%zd
",
offsetof(struct s, i), offsetof(struct s, c),
offsetof(struct s, d), offsetof(struct s, a));
printf("sizeof(struct s)=%zd
", sizeof(struct s));
exit(EXIT_SUCCESS);
}
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
GNU 2017-09-15 OFFSETOF(3)