winapi - gethostbyname and endianness - how are the bytes returned? -


on (intel) x86 machine, i've noticed if printf results of gethostbyname localhost, 100007f, though msdn documentation states should return ip in network byte order, aka big endian. searched bit , found this topic. based on answers there, i've deduced sequence of bytes same no matter endianness, so, localhost, i'd have in memory on both intel , amd chips:

7f|00|00|01

thus, reading memory intel chip results in 'reversed' result, while on amd cpu, i'd 0x7f000001. assumption correct? seems possible explanation, want make sure.

this code i'm using:

#define win32_lean_and_mean  #include <winsock2.h> #include <ws2tcpip.h> #include <stdio.h>  // need link ws2_32.lib #pragma comment(lib, "ws2_32.lib")  int main(int argc, char **argv) {      //-----------------------------------------     // declare , initialize variables     wsadata wsadata;     int iresult;      dword dwerror;     int = 0;      struct hostent *remotehost;     char *host_name;     struct in_addr addr;      char **palias;      // initialize winsock     iresult = wsastartup(makeword(2, 2), &wsadata);     if (iresult != 0) {         printf("wsastartup failed: %d\n", iresult);         return 1;     }      host_name = "localhost";       // if user input alpha name host, use gethostbyname()     // if not, host addr (assume ipv4)     if (isalpha(host_name[0])) {        /* host address name */         printf("calling gethostbyname %s\n", host_name);         remotehost = gethostbyname(host_name);     }     else {         printf("calling gethostbyaddr %s\n", host_name);         addr.s_addr = inet_addr(host_name);         if (addr.s_addr == inaddr_none) {             printf("the ipv4 address entered must legal address\n");             return 1;         }         else             remotehost = gethostbyaddr((char *)&addr, 4, af_inet);     }      if (remotehost == null) {         dwerror = wsagetlasterror();         if (dwerror != 0) {             if (dwerror == wsahost_not_found) {                 printf("host not found\n");                 return 1;             }             else if (dwerror == wsano_data) {                 printf("no data record found\n");                 return 1;             }             else {                 printf("function failed error: %ld\n", dwerror);                 return 1;             }         }     }     else {         printf("function returned:\n");         printf("\tofficial name: %s\n", remotehost->h_name);         (palias = remotehost->h_aliases; *palias != 0; palias++) {             printf("\talternate name #%d: %s\n", ++i, *palias);         }         printf("\taddress type: ");         switch (remotehost->h_addrtype) {         case af_inet:             printf("af_inet\n");             break;         case af_inet6:             printf("af_inet6\n");             break;         case af_netbios:             printf("af_netbios\n");             break;         default:             printf(" %d\n", remotehost->h_addrtype);             break;         }         printf("\taddress length: %d\n", remotehost->h_length);          if (remotehost->h_addrtype == af_inet) {             while (remotehost->h_addr_list[i] != 0) {                 addr.s_addr = *(u_long *)remotehost->h_addr_list[i++];                 printf("\tipv4 address #%d: %x %s\n", i, addr.s_addr, inet_ntoa(addr));             }         }         else if (remotehost->h_addrtype == af_inet6)             printf("\tremotehost ipv6 address\n");     }     getchar();     return 0; }

the output:

enter image description here


note: i've had friend run on amd cpu, , surprisingly, apparently it's 100007f him well. previous assumption wrong, or friend drunk?

the addresses contained in hostent structure in network byte order.

if have code suggests otherwise misinterpreting code , reaching wrong conclusion.

in network byte order, on little endian host, 127.0.0.1 0x0100007f. see how works, remember on little endian host, least significant byte stored first. that's 0x7f. bytes appear in order in memory, 0x7f, 0x00, 0x00, 0x01. , therefore represents 127.0.0.1.

now, same bytes on big endian host represent different 32 bit value. on big endian host, first byte if significant, , 0x7f, 0x00, 0x00, 0x01 represent value 0x7f000001.


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