Linux网络编程2——系统函数

#include <netinet/in.h>struct sockaddr
{
unsigned short sa_family; /*地址族*/
char sa_data[14]; /*14字节的协议地址，包含该socket的IP地址和端口号。*/
};
struct sockaddr_in
{
short int sa_family; /*地址族*/
unsigned short int sin_port; /*端口号*/
struct in_addr sin_addr; /*IP地址*/
unsigned char sin_zero[8]; /*填充0 以保持与struct sockaddr同样大小*/
};
struct in_addr
{
unsigned long int s_addr; /* 32位IPv4地址，网络字节序 */
};
#include <netinet/in.h>tips

sa_family:
AF_INET -> IPv4协议
AF_INET6 -> IPv6协议

SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h> int inet_aton(const char *cp, struct in_addr *inp);/* 注意，参数inp为传出参数 */
char *inet_ntoa(struct in_addr in);

/*************************************************************************
> File Name: test.c
> Author: KrisChou
> Mail:zhoujx0219@163.com
> Created Time: Wed 27 Aug 2014 11:06:11 PM CST
************************************************************************/#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>int main(int argc, char *argv[])
{
char ip_buf[] = "180.97.33.107";
struct in_addr my_addr;
inet_aton(ip_buf,&my_addr);
printf("ip : %s \n", ip_buf);
printf("net: %x \n", my_addr.s_addr);
return 0;
}

[purple@localhost 0827]$ gcc -o test test.c -Wall
[purple@localhost 0827]$ ./test
ip : 180.97.33.107
net: 6b2161b4

/*************************************************************************
> File Name: test1.c
> Author: KrisChou
> Mail:zhoujx0219@163.com
> Created Time: Wed 27 Aug 2014 11:43:26 PM CST
************************************************************************/#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>int main(int argc, char *argv[])
{
struct in_addr my_addr;
my_addr.s_addr = 0xb461216b;
printf("net: %x \n", my_addr.s_addr);
printf("ip : %s \n", inet_ntoa(my_addr));
return 0;
}

[purple@localhost 0827]$ gcc -o test1 test1.c -Wall
[purple@localhost 0827]$ ./test1
net: b461216b
ip : 107.33.97.180

SYNOPSIS
#include <netdb.h>
struct hostent *gethostbyname(const char *name);The hostent structure is defined in <netdb.h> as follows: struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses */
}
#define h_addr h_addr_list[0] /* for backward compatibility */ The members of the hostent structure are: h_name The official name of the host. h_aliases
An array of alternative names for the host, terminated by a NULL
pointer. h_addrtype
The type of address; always AF_INET or AF_INET6 at present. h_length
The length of the address in bytes. h_addr_list
An array of pointers to network addresses for the host (in net-
work byte order), terminated by a NULL pointer. h_addr The first address in h_addr_list for backward compatibility.

/*************************************************************************
> File Name: my_host.c
> Author: KrisChou
> Mail:zhoujx0219@163.com
> Created Time: Wed 27 Aug 2014 05:22:46 PM CST
************************************************************************/#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
int main(int argc, char* argv[])// exe hostname
{
struct hostent* p ;
p = gethostbyname(argv[1]) ;
/*
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]
*/
printf("host name: %s \n", p ->h_name); int index ;
char** pp = p -> h_aliases ;
for(index = 0 ; pp[index] != NULL; index ++ )
{
printf("alias : %s \n", pp[index]);
} printf("ip type : %d\n", p ->h_addrtype); printf("addr len : %d \n", p ->h_length); pp = p ->h_addr_list ;
for(index = 0; pp[index] != NULL ; index ++)
{
/* 由于h_addr_list是一个字符串指针数组，数组中存放的指针指向一个网络字节序
但是系统函数inet_ntoa需要传入的参数是一个结构体，因此需要进行转换。
pp[index]是一个char*类型的指针，先将其转换为struct in_addr*类型的指针，
接着去引用，即得到结构体。 */
printf("ip : %s \n", inet_ntoa( *(struct in_addr *)pp[index] ) );
} return 0 ;
}

[purple@localhost 0827]$ gcc -o myhost my_host.c -Wall
[purple@localhost 0827]$ ./myhost www.baidu.com
host name: www.a.shifen.com
alias : www.baidu.com
ip type : 2
addr len : 4
ip : 180.97.33.107
ip : 180.97.33.108

#include <stdio.h>
#include <stdlib.h>
int main()
{
int a = 0x61;//97
printf("%x\n",(char*)(&a)[0]);
}