int main (int argc, char **argv){
    int sockfd = socket(AF_INET,SOCK_STREAM,0);
    
    struct sockaddr_in addr;
    bzero(&addr,sizeof addr);
    addr.sin_family = AF_INET;
    addr.sin_port = htons(9999);
    struct hostent *server = gethostbyname("192.168.1.139");
    printf("%s %d\n",server->h_addr,inet_pton(AF_INET,server->h_addr,&addr.sin_addr.s_addr));
    int res = connect(sockfd,(struct sockaddr *)&addr,sizeof addr);
    printf("%d\n",res); 

    while (1){
        char buf[100] = "";
        fgets(buf,100,stdin);
        send(sockfd,buf,sizeof buf,0);
    }
}

If I execute this code, I always get:

$ ./client 
��� 0
-1

So:

1. Why I get these random chars? Why I don't see the IP string of h_addr?
2. Why the return of inet_pton is 0? It should be 1, 0 is for unsuccessfull, so why it fails?
3. Obviously, the connect fails.

Also, if instead of using inet_pton, I use this line:

bcopy((char *)server->h_addr,(char *)&addr.sin_addr.s_addr,h_length);

it works. BUT WHY it works this way and in the other way it doesn't??

CodePudding user response：

My English is not very good, so please understand.

See gethostbyname() man page.

The gethostbyname() function returns a structure of type hostent for the given host name. Here name is either a hostname or an IPv4 address in standard dot notation (as for inet_addr(3)). If name is an IPv4 address, no lookup is performed and gethostbyname() simply copies name into the h_name field and its struct in_addr equivalent into the h_addr_list[0] field of the returned hostent structure.

h_addr_list[0] is struct in_addr and h_addr_list[0] is h_addr, See below.

struct hostent

struct  hostent {
 char *  h_name;     
 char ** h_aliases; 
 int     h_addrtype;  
 int     h_length;    
 char ** h_addr_list;
};

#define h_addr  h_addr_list[0]

struct in_addr

struct in_addr {
  uint32_t s_addr;
}

So, if you want to see the IP string of h_addr, see the code below.

printf("%s\n", inet_ntoa(*(struct in_addr*)server->h_addr));

And you can use it by assigning the value of s_addr as addr.sin_addr.s_addr = *(unit32_t *)server->haddr;

Or you can make it simpler using addr.sin_addr.s_addr = inet_addr("192.168.1.139");