Getting IPV4 address from a sockaddr structure

Question

How can I extract an IP address into a string  I can t find a reference that tells me how char sa data 14  is encoded

User · Answer

You can use getnameinfo for Windows and for Linux   Assuming you have a good  i e  it s members have appropriate values  sockaddr  called pSockaddr   char clienthost NI MAXHOST      The clienthost will hold the IP address  char clientservice NI MAXSERV   int theErrorCode   getnameinfo pSockaddr  sizeof  pSockaddr   clienthost  sizeof clienthost   clientservice  sizeof clientservice   NI NUMERICHOST NI NUMERICSERV    if  theErrorCode    0           There was an error      cout  lt  lt  gai strerror e1   lt  lt  endl   else        Print the info      cout  lt  lt   The ip address is      lt  lt  clienthost  lt  lt  endl      cout  lt  lt   The clientservice      lt  lt  clientservice  lt  lt  endl

User · Answer

Once sockaddr cast to sockaddr in  it becomes this   struct sockaddr in       u short     sin family      u short     sin port      struct      in addr sin addr      char        sin zero 8

User · Answer

Type casting of sockaddr to sockaddr in and retrieval of ipv4 using inet ntoa  char   ip   inet ntoa   struct sockaddr in   sockaddr - gt sin addr

User · Answer

Emil s answer is correct  but it s my understanding that inet ntoa is deprecated and that instead you should use inet ntop  If you are using IPv4  cast your struct sockaddr to sockaddr in  Your code will look something like this   struct addrinfo  res       populated elsewhere in your code struct sockaddr in  ipv4    struct sockaddr in   res- gt ai addr  char ipAddress INET ADDRSTRLEN   inet ntop AF INET   amp  ipv4- gt sin addr   ipAddress  INET ADDRSTRLEN    printf  The IP address is   s n   ipAddress     Take a look at this great resource for more explanation  including how to do this for IPv6 addresses

User · Answer

Just cast the entire sockaddr structure to a sockaddr in  Then you can use   char  ip   inet ntoa their addr sin addr    To retrieve the standard ip representation

User · Answer

inet ntoa   works for IPv4  inet ntop   works for both IPv4 and IPv6   Given an input struct sockaddr  res  here are two snippets of code  tested on macOS    Using inet ntoa     include  lt arpa inet h gt   struct sockaddr in  addr in    struct sockaddr in   res  char  s   inet ntoa addr in- gt sin addr   printf  IP address   s n   s     Using inet ntop     include  lt arpa inet h gt   include  lt stdlib h gt   char  s   NULL  switch res- gt sa family        case AF INET            struct sockaddr in  addr in    struct sockaddr in   res          s   malloc INET ADDRSTRLEN           inet ntop AF INET   amp  addr in- gt sin addr   s  INET ADDRSTRLEN           break            case AF INET6            struct sockaddr in6  addr in6    struct sockaddr in6   res          s   malloc INET6 ADDRSTRLEN           inet ntop AF INET6   amp  addr in6- gt sin6 addr   s  INET6 ADDRSTRLEN           break            default          break    printf  IP address   s n   s   free s

[c] Getting IPV4 address from a sockaddr structure

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