Network Programming - Passing Character Pointers

[gerard4143]

I have a simple question about passing character pointers through sockets.

example code/data

struct mystr
{
	unsigned int one;
	unsigned two two;
	char *ch;
};

unsigned int strsize;//character array size

struct mystr thestr;

thestr.one = 1234;
thestr.two = 5678;
thestr.ch = (char*)malloc(strsize * sizeof(char));

...copy data to new char pointer - thestr.ch

Lets say I have a data structure like the above definition, the way I would pass this data set would be to:

write(serverfd, (char*)&thestr, 2 * sizeof(unsigned int));//write both unsigned int one and two
write(serverfd, (char*)&strsize, sizeof(unsigned int));//send the size of the character array  
write(serverfd, thestr.ch, strlen(thestr.ch));//write the character array

Now I'm able to recreate the data on the server side with no problems but is this the proper way of passing a structure that contains a character array?

The textbook I have has very info on this(none that I can find) and I can't find anything Googling.

[Rubberman]

This will work if (and only if) both systems (client and server) are running the same hardware and operating system. Typically, for network programming, non-character data, such as the integer parameters, are converted to/from network byte order. That way, a client can be a little endian system, such as Intel x86, and the server can be a big endian system, such as a Sun Sparc.

The following is the Linux man page for the functions that let you do this properly:

BYTEORDER(3)               Linux Programmer’s Manual              BYTEORDER(3)

NAME
       htonl,  htons,  ntohl,  ntohs  - convert values between host and network byte
       order

SYNOPSIS
       #include <arpa/inet.h>

       uint32_t htonl(uint32_t hostlong);

       uint16_t htons(uint16_t hostshort);

       uint32_t ntohl(uint32_t netlong);

       uint16_t ntohs(uint16_t netshort);

DESCRIPTION
       The htonl() function converts the unsigned integer hostlong  from  host  byte
       order to network byte order.

       The  htons() function converts the unsigned short integer hostshort from host
       byte order to network byte order.

       The ntohl() function converts the unsigned integer netlong from network  byte
       order to host byte order.

       The  ntohs()  function converts the unsigned short integer netshort from net-
       work byte order to host byte order.

       On the i80x86 the host byte order is Least Significant  Byte  first,  whereas
       the  network  byte  order,  as used on the Internet, is Most Significant Byte
       first.

CONFORMING TO
       POSIX.1-2001.

       Some  systems  require   the   inclusion   of   <netinet/in.h>   instead   of
       <arpa/inet.h>.

SEE ALSO
       gethostbyname(3), getservent(3)

BSD                               1993-04-15                      BYTEORDER(3)

[gerard4143]

Thanks for the reply Rubberman. I almost(well I did) forgot about byte order.

So as far as I can tell passing pointers through a socket is a matter of a common data set between sender and receiver.i.e receiver expects a data set of a certain format and the sender is expected to send a data set in that 'certain' format.

Thanks again for the heads up on bytes order.