Hex IP to Decimal IP conversion

Question

How can I convert a hex ip (such as 42477f35), and get it to spit out the correct decimal ip (in the example before, the correct result is 66.71.127.53

Answer 1

You could use sscanf to pick the hexadecimal out of the original string as integers and then use sprintf to put them into another string in the proper format.

sscanf(hexipstring, "%2x%2x%2x%2x", &uint0, &uint1, &uint2, &uint3);
sprintf("%u.%u.%u.%u", uint0, uint1, uint2, uint3);

Or something like that. i'm never really sure with scanf, so read through some man pages. The "%2x" should tell scanf to use 2 characters at most and interpret them as a hexadecimal number.

-edit: Caf's code is better since it checks for errors in sscanf and uses snprintf rather than sprintf. More errorproof. Use it instead of mine.

Answer 2

This is one possibility:

#include <stdio.h>

int ip_hex_to_dquad(const char *input, char *output, size_t outlen)
{
    unsigned int a, b, c, d;

    if (sscanf(input, "%2x%2x%2x%2x", &a, &b, &c, &d) != 4)
        return -1;

    snprintf(output, outlen, "%u.%u.%u.%u", a, b, c, d);
    return 0;
}

Answer 3

Split the hex ip into octets (two hex digits at a time), and convert each octet to a decimal integer.