- Converting a
"Dotted Decimal Notation" string
(such as "170.140.151.110") to
a binary IP address :
- int
inet_addr("xxx.xxx.xxx.xxx")
- Input:
- A string
with
a dotted decimal IP address
E.g.: inet_addr("170.140.151.110")
- A string
with
a dotted decimal IP address
- Output:
- The corresponding binary
IP address in
network byte order
- Returns −1 if the input string does not contain a dotted decimal IP address
- The corresponding binary
IP address in
network byte order
Example:
struct sockaddr_in dest_addr; dest_addr.sin_addr.s_addr = inet_addr("170.140.151.110"); - Input:
- int
inet_addr("xxx.xxx.xxx.xxx")
- Important note:
- Do not
use
htonl( )
on the output of
inet_addr( )
Because:
- the output of inet_addr( ) is already in network byte ordering !!!
- Do not
use
htonl( )
on the output of
inet_addr( )
- Converting a binary IP address
back to a
"Dotted Decimal Notation" string
(such as
"170.140.151.110"):
- char * inet_ntoa(int)
- Input:
- A binary IP address in network byte ordering
- Output:
- A string containing dotted decimal representation of the input IP address
- Input:
Example:
Suppose: struct sockaddr_in dest_addr; contains an IP address in network byte order
char IPaddr[100]; strcpy(IPaddr, inet_ntoa(dest_addr.sin_addr.s_addr) ); - char * inet_ntoa(int)
- The following figure
summarizes
the operation
of the
inet_addr()
and inet_ntoa()
functions:
- The UDP sender using
dotted decimal IP address to
specify the receiver:
int main(int argc, char **argv) { struct sockaddr_in dest_addr; /* Destination socket address */ ... /* ============================================================= argv[1] is the string containg the dotted decimal IP address ============================================================= */ if ( ( dest_addr.sin_addr.s_addr = inet_addr( argv[1] ) ) == -1 ) { printf("Dotted IP-address must be of the form a.b.c.d\n"); exit(1); } ... }
- Example Program:
(Demo above code)
- Sender: /home/cs455001/demo/netw-prog-ipv4/udp4-s2.c
- Receiver: /home/cs455001/demo/netw-prog-ipv4/udp4-r2.c
- The new UDP sender using dotted decimal IP address Prog file: click here
- The (unmodified) UDP receiver Prog file: click here
How to run the program:
- To compile the sender: gcc -o udp4-s2 udp4-s2.c -lnsl
- To compile the receiver:
gcc -o udp4-r2 udp4-r2.c
- To run the receiver: udp4-r2 port#
- To run the sender: udp4-s2 xx.xx.xx.xx port#