#includestruct in_addr { in_addr_t s_addr; //32-bit IPv4 address,BE};struct sockaddr_in { uint8_t sin_len; //该结构长度 16-bit sa_family_t sin_family; //AF_INET in_port_t sin_port; //端口号 struct in_addr sin_addr; //32-bit IP地址 char sin_zero[8]; //保留};
通过域名获取IP地址，IP地址两个表达方式的转换（点分十进制，数值格式，eg:255.255.0.0---0x0000FFFF(网络字节序）），字节序的转换
socket编程接口
#include#include //通过域名获取IP地址struct hostent *gethostbyname(const char *name);/* name:域名，eg:"www.baidu.com"*///通过二进制的IP地址找到对应的域名struct hostent *gethostbyaddr(const void *addr, socklen_t len, int type);/* addr:二进制ip len:ip长度，对于IPv4是4 type:AF_INET*/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 */}/* char* 字符串都是以 '\0' 结束的 char** 字符串指针都是以 NULL 结束的*///ip地址格式转换#include //点分十进制转换为数值形式int inet_pton(int af, const char *src, void *dst);/* af: AF_INET/AF_INET6，对应IPv4/IPv6 src: 点分十进制字符串，eg: "255.255.0.0" dst: 存放转换结果的，对应解析为 0x0000FFFF,大端 返回：成功，1；src无效，0；出错，-1；*///数值形式转换为点分十进制形式const char *inet_ntop(int af, const void *src, char *dst, socklen_t size);/* src:网络字节序，二进制形式，eg: 0x0000ffff dst:存放转换结果，点分十进制字符串 size:指定字符串长度 返回：成功，dst;出错，NULL*///主机字节序和网络字节序转换#include uint32_t htonl(uint32_t hostlong);uint16_t htons(uint16_t hostshort);uint32_t ntohl(uint32_t netlong);uint16_t ntohs(uint16_t netshort);
使用例子
#include#include #include #include void printHostent(struct hostent *p){ printf("%s\n",p->h_name); char **q=p->h_aliases; while(*q!=NULL){ printf("%s\n",*q); ++q; } printf("%d %d\n",p->h_addrtype,p->h_length); q=p->h_addr_list; char str[16]; while(*q!=NULL){ printf("%s\n",inet_ntop(AF_INET,*q,str,16)); //printf("%s\n",str); ++q; } }int main(){ printf("struct hostent of www.baidu.com:\n"); char *host="www.baidu.com"; struct hostent *p=gethostbyname(host); if(p==NULL) printf("gethostbyname failed\n"); else printHostent(p); printf("\npresentation ip---numeric ip\n"); unsigned int a; inet_pton(AF_INET,"255.255.0.0",&a); printf("numeric ip network byte order: %x\n",a); printf("host byte order: %x\n",ntohl(a)); char str[16]; inet_ntop(AF_INET,&a,str,16); printf("presentation ip: %s\n",str);}