inet_ntoa problem

I am declaring following variables

unsigned long   dstAddr;
unsigned long   gateWay;
unsigned long   mask;

These variables contains ipaddresses in network byte order. So when I am trying to print the dot notation using inet_ntoa function 开发者_如何转开发for mask variable sometimes it is printing strange values. The below code is in a while loop .. which loops for n times.

printf("%s\t%s\t%s\t",inet_ntoa(dstAddr),inet_ntoa(gateWay),inet_ntoa(mask));

  192.168.122.0         0.0.0.0    0.255.255.255    

but it should be

  192.168.122.0         0.0.0.0    255.255.255.0

I printed the HEX values of the variables and it shows ..

007aa8c0    00000000      ffffff00  

So is this because of inet_ntoa ??

Actually I am trying to get the values of the declared variables from 254 routing table in kernel via NETLINKS. I guess I should still use inet_ntoa function to convert the value into dot notation .. ??

The only thing that makes sense is that your assumption regarding all the addresses being in network byte order is incorrect.

Well, given that it works for your non-mask values (including the first which also has the high bit set), I'd be looking at what mask actually contains.

What is it when you print it out as a normal unsigned long? My bet is that mask is actually not the correct value:

printf ("%08x\t%08x\t%08x\n", dstAddr, gateWay, mask);

(assuming you have four-byte longs).

For example, this little program (compiled under Cygwin):

#include <stdio.h>

int main (void) {
    unsigned long dstAddr, gateWay, mask;
    dstAddr = 0x007aa8c0;
    gateWay = 0x00000000;
    mask    = 0x00ffffff;

    printf("%-15s %-15s %-15s\n",
        inet_ntoa (dstAddr),
        inet_ntoa (gateWay),
        inet_ntoa (mask));

    printf("%-15s ",  inet_ntoa (dstAddr));
    printf("%-15s ",  inet_ntoa (gateWay));
    printf("%-15s\n", inet_ntoa (mask));

    printf ("%08x%8s%08x%8s%08x\n",
        dstAddr, "",
        gateWay, "",
        mask);

    return 0;
}

outputs:

192.168.122.0   192.168.122.0   192.168.122.0
192.168.122.0   0.0.0.0         255.255.255.0
007aa8c0        00000000        00ffffff

Note that I had to separate my calls to inet_ntoa as it appears to use a static buffer. When I was doing it all within a single printf, it overwrote the contents of that buffer before any of them were printed, hence I only got the last one processed. I don't think that's happening in your case since you're getting different values.

I also have the same problem with you. Use inet_ntop() and inet_pton() if you need it other way around. Do not use inet_ntoa(), inet_aton() and similar as they are deprecated and don't support ipv6. see link: convert Ip address int to string