gethostbyname

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#include <netdb.h>   /*返回：若成功则为非空指针，若出错则为NULL且设置h_errno*/ struct hostent *gethostbyname(const char *hostname);   struct hostent {         char *h_name;           /*official name of host*/         char **h_aliases;       /*pointer to array of pointers to alias names*/         int h_addrtype;         /*host address type: AF_INET*/         int h_length;           /*length of address: 4*/         char **h_addr_list;     /*ptr to array of ptrs with IPv4 addrs*/ };

当发生错误时，它不设置errno变量，而是将全局变量h_errno设置为在头文件<netdb.h>中定义的下列常值之一：

HOST_NOT_FOUND;

TRY_AGAIN;

NO_RECOVERY;

NO_DATA;

gethostbyname执行的是对A记录的查询，它只能返回IPv4地址。