inet_ntoa用法如下:
char *inet_ntoa(struct in_addr in);
就是将struct in_addr結構轉換為IP位址的形式,struct in_addr這個結構應該不陌生吧,它的定義如下:
struct in_addr{
unsigned long s_addr;
}
struct sockaddr_in {
short int sin_family;
unsigned short int sin_port;
struct in_addr sin_addr;
unsigned char sin_zero[8];
};
在伺服器端使用accept函數之後,會得到用戶端連接配接的struct sockaddr結構,然後将其轉換成struct sockaddr_in結構,此時可以在伺服器端得到用戶端連接配接的IP和端口資料。
這時用這個函數有一個問題是:如果在64位的機器上,使用
char* tmp = inet_ntoa(sin->sin_addr);
之後,對tmp進行操作,會出現斷錯誤,但在32位機器上沒有問題,原因是64位時inet_ntoa傳回值是一個整型。
在網上找的兩種解決辦法:
- 在使用的檔案中,引用#include <arpa/inet.h>頭檔案。
- 直接使用inet_ntop函數。
inet_ntop的說明如下:
NAME
inet_ntop - Parse network address structures
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
const char *inet_ntop(int af, const void *src,
char *dst, socklen_t cnt);
DESCRIPTION
This function converts the network address structure src in the af address family into a char-
acter string, which is copied to a character buffer dst, which is cnt bytes long.
inet_ntop(3) extends the inet_ntoa(3) function to support multiple address families,
inet_ntoa(3) is now considered to be deprecated in favor of inet_ntop(3). The following
address families are currently supported:
AF_INET
src points to a struct in_addr (network byte order format) which is converted to an IPv4
network address in the dotted-quad format, "ddd.ddd.ddd.ddd". The buffer dst must be at
least INET_ADDRSTRLEN bytes long.
AF_INET6
src points to a struct in6_addr (network byte order format) which is converted to a rep-
resentation of this address in the most appropriate IPv6 network address format for this
address. The buffer dst must be at least INET6_ADDRSTRLEN bytes long.
RETURN VALUE
inet_ntop() returns a non-null pointer to dst. NULL is returned if there was an error, with
errno set to EAFNOSUPPORT if af was not set to a valid address family, or to ENOSPC if the con-
verted address string would exceed the size of dst given by the cnt argument.
CONFORMING TO
POSIX.1-2001. Note that RFC 2553 defines a prototype where the last parameter cnt is of type
size_t. Many systems follow RFC 2553. Glibc 2.0 and 2.1 have size_t, but 2.2 has socklen_t.