sock_ntop.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/un.h>
#include <arpa/inet.h>
#include <sys/socket.h>

char *sock_ntop(const struct sockaddr *sa, socklen_t salen) {
    
    char portstr[8];    
    static char str[128];
   
    switch (sa->sa_family) {
        case AF_INET: {
            struct sockaddr_in    *sin = (struct sockaddr_in *) sa;

            if (inet_ntop(AF_INET, &sin->sin_addr, str, 
                sizeof(str)) == NULL) {
                return(NULL);
            }
            if (ntohs(sin->sin_port) != 0) {
                snprintf(portstr, sizeof(portstr), ":%d", 
                    ntohs(sin->sin_port));
                strcat(str, portstr);
            }
            return(str);
        }
        case AF_INET6: {
            struct sockaddr_in6    *sin6 = (struct sockaddr_in6 *) sa;

            str[0] = '[';
            if (inet_ntop(AF_INET6, &sin6->sin6_addr, str + 1, 
                sizeof(str) - 1) == NULL) {
                return(NULL);
            }
            if (ntohs(sin6->sin6_port) != 0) {
                snprintf(portstr, sizeof(portstr), "]:%d",
                    ntohs(sin6->sin6_port));
                strcat(str, portstr);
                return(str);
            }
            return (str + 1);
        }
        case AF_UNIX: {
            struct sockaddr_un    *unp = (struct sockaddr_un *) sa;

            if (unp->sun_path[0] == 0) {
                strcpy(str, "(no pathname bound)");
            } else {
                snprintf(str, sizeof(str), "%s", unp->sun_path);
            }
            return(str);
        }
        default: {
            snprintf(str, sizeof(str), "sock_ntop: unknown AF_xxx: %d, len %d",
                 sa->sa_family, salen);
            return(str);
        }
    }
    return (NULL);
}

函数功能：从套接字地址结构中取出IP地址和端口号，返回值为字符串【IP:端口号】的地址指针