linux网络编程一

linux网络编程一 大小端

小端字节序：高位字节存储在内存的高地址处，也称为 主机字节序 PC机大多采用此模式
大端字节序：高位字节存储在内存的低地址处，也称为 网络字节序；网络端传输

大小端的不一致需要转换

字节序 IP地址与端口port转换

#include 
uint32_t htonl(uint32_t hostlong);//IP 主机->网络
uint16_t htons(uint16_t hostshort);//port 主机->网络
uint32_t ntohl(uint32_t netlong);//IP 网络->主机
uint16_t ntohs(uint16_t netshort);//port 网络->主机

IP地址转换

需要做的一些列转换192.168.0.1->string->atoi->int->htinl->网络
直接使用函数 inet_pton，inet_ntop

#include

convert IPv4 and IPv6 addresses from text to binary form

int inet_pton(int af, const char *src, void *dst);//本机->网络字节序

convert IPv4 and IPv6 addresses from binary to text form

const char *inet_ntop(int af, const void *src, char *dst, socklen_t size);//网络字节序->本机

网络字节序的转换

#include
#include
#include
#include

union{
        short value;
        char union_bytes[sizeof(short)];
}test;
//确认大端还是小端
void byteorder()
{
        test.value=0x1122;

        if(test.union_bytes[0]==0x11 && test.union_bytes[1]==0x22)
        {
                printf("big endiann");
        }
        else if(test.union_bytes[0]==0x22 && test.union_bytes[1]==0x11)
        {
                printf("little endiann");
        }
        else
        {
                printf("unknown");
        }
}
//宏定义函数，实现大小端转化怒
#define BLSwap16(a) ((((a&0xff00)>>8) | (a&0x00ff)<<8))
#define BLSwap32(a) (((a&0xff000000)>>24) | ((a&0x00ff0000)>>8) | ((a&0x0000ff00)<<8)|((a&0x000000ff)<<24))

void main()
{
        byteorder();


        short a = 0x1234;
        short b = htons(a);
        printf("short b=%xn",b);

        b = BLSwap16(a);
        printf("BLSwap short b=%xn",b);

        int c = 0x12345678;
        int d = htonl(c);
        printf("long int d=%xn",d);
        d = BLSwap32(c);

        printf("BLSwap32 long int d=%xn",d);
}

输出结果

(base) wy@ubuntu:~/network$ ./a.out 
little endian
short b=3412
BLSwap short b=3412
long int d=78563412
BLSwap32 long int d=78563412

IP地址转换

#include 
#include 
#include 
#include 

int   main(int argc, char *argv[])
       {
           unsigned char buf[sizeof(struct in6_addr)];
           int domain, s;
           char str[INET6_ADDRSTRLEN];

           if (argc != 3) {
               fprintf(stderr, "Usage: %s {i4|i6|} stringn", argv[0]);
               exit(EXIT_FAILURE);
           }

           domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :
                    (strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);

           s = inet_pton(domain, argv[2], buf);
           if (s <= 0) {
               if (s == 0)
                   fprintf(stderr, "Not in presentation format");
               else
                   perror("inet_pton");
               exit(EXIT_FAILURE);
           }
            if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {
               perror("inet_ntop");
               exit(EXIT_FAILURE);
           }

           printf("%sn", str);

           exit(EXIT_SUCCESS);


       }

(base) wy@ubuntu:~/network$ ./a.out i6 1:0:0:0:0:0:0:8
1::8
(base) wy@ubuntu:~/network$ ./a.out i6 0:0:0:0:0:FFFF:204.152.189.116
::ffff:204.152.189.116
(base) wy@ubuntu:~/network$ ./a.out i6 0:0:0:0:0:0:0:0
::