IP conversion of Linux networks

An IP address is represented by a decimal number separated by a decimal point, which we call dotted decimal notation. Each of these decimal numbers represents a single byte of unsigned value (according to the network byte order) because each byte is an unsigned 8-bit value, which limits the range that each byte can represent is 0~255.

A special IP

• Each byte is a 0 address ("0.0.0.0") corresponding to the current host;
• Each byte in the IP address is a 1 IP address ("255.255.255.255") that is the broadcast address of the current subnet;
• IP address in any of the "11110" beginning of the class E IP address are reserved for future and experimental use;
• The IP address can not start with the decimal "127", the address of the number 127.0.0.1 to 127.255.255.255 for loop testing, such as 127.0.0.1 can represent the native IP address;
• The first 8-bit group of the network ID also cannot have all "0", and the full "0" represents the local network.

related functions for manipulating IP addresses in_addr_t inet_addr (const char *string);
This function uses string as the input parameter and converts the dot-decimal IP address into an integer value based on the network byte order. The function returns the IP address of the binary network byte order (struct In_add), otherwise returns Inaddr_none (-1).
Example:

#include <arpa/inet.h> #include <stdio.h> #include <stdlib.h>int main (int argc, char *argv[]) {struct IN_ADDR addr;if (argc! = 2) {fprintf (stderr, "%s <dotted-address>\n", argv[0]); exit (exit_failure);} if ((addr.s_addr = inet_addr (argv[1])) = =-1) {fprintf (stderr, "%s is Invalid address\n", argv[1]);} else{fprintf (stdout, "%u\n", addr.s_addr);} return 0;} Note: If the IP address is 255.255.255.255. Then 1 is returned after calling the Inet_addr () function (since the complement of-1 is 0xFFFFFFFF). It is therefore not recommended to use the INET_ADDR () function. Instead, use the Inet_aton () function.

int Inet_aton (const char *string, strcut in_addr *addr);
Converts the IP address of a dotted decimal string type stored in string to a binary IP address, and the converted value is stored in the struct in_addr that the pointer addr points to. The function execution successfully returns a value other than 0, and the failure returns 0.
Example:

#include <stdio.h> #include <arpa/inet.h> #include <stdlib.h>int main (int argc, char *argv[]) {if (argc ! = 2) {fprintf (stderr, "%s <dotted-address>\n", argv[0]); exit (exit_failure);} struct IN_ADDR addr;if (Inet_aton (argv[1],&addr)! = 0) fprintf (stdout, "%u\n", addr.s_addr); elsefprintf (stdout, "%s Invalid address\n ", argv[1]); return 0;}

Char *inet_ntoa (strcut in_addr addr);
Converts a 32-bit binary IP address into a dotted-decimal string form. The function execution succeeds returns the string, and the failure returns NULL.

#include <stdio.h> #include <arpa/inet.h> #include <stdlib.h>int main (int argc, char *argv[]) {if (argc ! = 2) {fprintf (stderr, "%s <dotted-address>\n", argv[0]); exit (exit_failure);} struct IN_ADDR addr;if (Inet_aton (argv[1],&addr) = = 0) {fprintf (stderr, "%s Invalid address\n", argv[1]); Exit (Exit_ FAILURE);} printf ("%s\n", Inet_ntoa (addr)); return 0;}

in_addr_t inet_network (const char *STR);
Converts the network address of the string form of the parameter str to the host byte-order binary IP address (ignoring the size side). After the successful return of the converted result, the failure returns-1. Example:

#include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdlib.h>int main ( int argc, char *argv[]) {if (argc! = 2) {fprintf (stderr, "%s <dotted-address>\n", argv[0]); exit (exit_failure);} struct in_addr addr;if ((addr.s_addr = Inet_network (argv[1])) = =-1) {fprintf (stderr, "%s Invalid address\n", argv[1]); Exit (exit_failure);} else{fprintf (stdout, "%u \ n", addr.s_addr);} return 0;}

in_addr_t inet_lnaof (struct in_addr addr);
Extracts the host address from the parameter addr and executes a host address that successfully returns the host's byte-order form.
such as: 192.168.1.1 belongs to Class C address, the host address is 1.
Example:

#include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdlib.h>int main ( int argc, char *argv[]) {if (argc! = 2) {fprintf (stderr, "%s <dotted-address>\n", argv[0]); exit (exit_failure);} struct in_addr addr;if ((addr.s_addr = Inet_network (argv[1])) = =-1) {fprintf (stderr, "%s Invalid address\n", argv[1]); Exit (exit_failure);} ADDR.S_ADDR = htonl (ADDR.S_ADDR); fprintf (stdout, "0x%x \ n", inet_lnaof (addr)); return 0;}

in_addr_t inet_netof (struct in_addr addr);
Extracts the network address from the parameter addr, performing a successful return of the network address in the host byte order form.
For example: 192.168.1.1 belongs to class C address, the network address is 0x c0a801.
Example:

#include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdlib.h>int main ( int argc, char *argv[]) {if (argc! = 2) {fprintf (stderr, "%s <dotted-address>\n", argv[0]); exit (exit_failure);} struct in_addr addr;if ((addr.s_addr = Inet_network (argv[1])) = =-1) {fprintf (stderr, "%s Invalid address\n", argv[1]); Exit (exit_failure);} printf ("0x%x\n", addr.s_addr); addr.s_addr = htonl (ADDR.S_ADDR); fprintf (stdout, "0x%x \ n", Inet_netof (addr)); return 0;}

struct IN_ADDR inet_makeaddr (int net, int host);
Merges the host byte-order network address NET with the host address host into a network byte-order IP address.
Example:

#include <stdio.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdlib.h>int main ( int argc, char *argv[]) {if (argc! = 2) {fprintf (stderr, "%s <dotted-address>\n", argv[0]); exit (exit_failure);} struct IN_ADDR addr, addr_1;if ((addr.s_addr = Inet_network (argv[1])) = =-1) {fprintf (stderr, "%s Invalid address\n", argv[ 1]); exit (exit_failure);} ADDR.S_ADDR = htonl (addr.s_addr); uint32_t net = inet_netof (addr); uint32_t host = inet_lnaof (addr); addr_1 = Inet_makeaddr (net,host);p rintf ("0x%x \ n", htonl (ADDR_1.S_ADDR)); return 0;}

IP conversion of Linux networks