将整数值转换为ip-address

Question

How to convert a 32-bit integer value to an ip-address?

I am having int value=570534080 and want to convert it to 192.168.1.34 .

Answer 1

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int main(void) {
    int value=570534080;
    struct in_addr addr = {value};
    printf( "%s", inet_ntoa( addr ) );
    return 0;
}

Test: http://ideone.com/RCDgj4

For Windows use #include <winsock2.h>

Answer 2

A 32-bit integer here, 570534080 , can be splitted into four 8-bit unsigned integers, which are exact the IP address.

int value =  570534080; // which is 0x2201a8c0 (0x22, 0x01, 0xa8, 0xc0)
unsigned char *ip = &value;
/* then */
ip[0] == 192;
ip[1] == 168;
ip[2] == 1;
ip[3] == 34;    

Please notice the endian (big endian / little endian), which makes @KerrekSB's answer reversed.

EDITED:

Let's making it clearer.

When talking about IP address and integers, there're actually TWO types of integers we concern about:

1. The integer representation of the IP address: 192.168.1.34 <==> (((192 * 256 + 168) * 256 + 1) * 256 + 34
2. The actual data (bit stream maybe) you receive and interpreted in an 32-bit integer, like what this OP provides: 570534080 <==> (0x22, 0x01, 0xa8, 0xc0)(on a little-endian machine) <==> (34.1.168.192) .

PLEASE NOTICE THIS IS PLATFORM SPECIFIC AND DANGEROUS! Since this relies on the byte order of an integer number, which is called endianess.

AGAIN EDITED:

Here I'd vote for @DavidHeffernan's comment, which is to use inet_ntoa .