Linux/UNIX C 错误函数 h_errno 以及库函数 netdb.h 详细介绍

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NAME

    netdb.h - definitions for network database operations

SYNOPSIS

    #include

DESCRIPTION

    The header may define the in_port_t type and the in_addr_t type as described in .

    The header shall define the hostent structure that includes at least the following members:
    har   *h_name       Official name of the host.
    char  **h_aliases    A pointer to an array of pointers to
                                  alternative host names, terminated by a 
                                  null pointer. 
    int     h_addrtype         Address type. 
    int     h_length             The length, in bytes, of the address.
    char  **h_addr_list       A pointer to an array of pointers to network 
                                        addresses (in network byte order) for the host,
                                        terminated by a null pointer. 


    The header shall define the netent structure that includes at least the following members:
    char       *n_name      Official, fully-qualified (including the 
                                       domain) name of the host. 
     char      **n_aliases    A pointer to an array of pointers to  
                                        alternative network names, terminated by a 
                                        null pointer. 
    int           n_addrtype   The address type of the network. 
    uint32_t  n_net            The network number, in host byte order. 


    The uint32_t type shall be defined as described in .

     The header shall define the protoent structure that includes at least the following members:
    char   *p_name     Official name of the protocol.
    char  **p_aliases   A pointer to an array of pointers to 
                                 alternative protocol names, terminated by 
                                 a null pointer. 
    int     p_proto            The protocol number.


    The header shall define the servent structure that includes at least the following members:
     char   *s_name     Official name of the service. 
    char  **s_aliases  A pointer to an array of pointers to
                                alternative service names, terminated by 
                                 a null pointer. 
    int     s_port         The port number at which the service
                                 resides, in network byte order. 
    char   *s_proto      The name of the protocol to use when 
                                 contacting the service. 


    The header shall define the IPPORT_RESERVED macro with the value of the highest reserved     Internet port number.

    [OB]  When the header is included, h_errno shall be available as a modifiable lvalue of type int. It     is unspecified whether h_errno is a macro or an identifier declared with external linkage.

    The header shall define the following macros for use as error values for gethostbyaddr() and     gethostbyname():

                HOST_NOT_FOUND
                NO_DATA
                NO_RECOVERY
                TRY_AGAIN

Address Information Structure

    The header shall define the addrinfo structure that includes at least the following members:
    int                           ai_flags                 Input flags. 
    int                           ai_family               Address family of socket. 
    int                           ai_socktype           Socket type.
    int                           ai_protocol            Protocol of socket. 
    socklen_t                 ai_addrlen             Length of socket address. 
    struct sockaddr      *ai_addr                 Socket address of socket. 
    char                        *ai_canonname      Canonical name of service location.
    struct addrinfo        *ai_next                 Pointer to next in list. 


    The header shall define the following macros that evaluate to bitwise-distinct integer constants     for use in the flags field of the addrinfo structure:
        AI_PASSIVE
                Socket address is intended for bind().
        AI_CANONNAME
                Request for canonical name.
        AI_NUMERICHOST
                Return numeric host address as name.
        AI_NUMERICSERV
                Inhibit service name resolution.
        AI_V4MAPPED
                If no IPv6 addresses are found, query for IPv4 addresses and return them to the caller as IPv4-                mapped IPv6 addresses.
        AI_ALL
                Query for both IPv4 and IPv6 addresses.
        AI_ADDRCONFIG
                Query for IPv4 addresses only when an IPv4 address is configured; query for IPv6 addresses only                 when an IPv6 address is configured.

    The header shall define the following macros that evaluate to bitwise-distinct integer constants     for use in the flags argument to getnameinfo():
        NI_NOFQDN
                Only the nodename portion of the FQDN is returned for local hosts.
        NI_NUMERICHOST
                The numeric form of the node's address is returned instead of its name.
        NI_NAMEREQD
                Return an error if the node's name cannot be located in the database.
        NI_NUMERICSERV
                The numeric form of the service address is returned instead of its name.
        NI_NUMERICSCOPE
                For IPv6 addresses, the numeric form of the scope identifier is returned instead of its name.
        NI_DGRAM
                Indicates that the service is a datagram service (SOCK_DGRAM).

Address Information Errors

    The header shall define the following macros for use as error values for getaddrinfo() and     getnameinfo():
            EAI_AGAIN
                    The name could not be resolved at this time. Future attempts may succeed.
            EAI_BADFLAGS
                    The flags had an invalid value.
            EAI_FAIL
                    A non-recoverable error occurred.
            EAI_FAMILY
                    The address family was not recognized or the address length was invalid for the specified family.
            EAI_MEMORY
                    There was a memory allocation failure.
            EAI_NONAME
                    The name does not resolve for the supplied parameters.

                     NI_NAMEREQD is set and the host's name cannot be located, or both nodename and servname                                               were null.
            EAI_SERVICE
                        The service passed was not recognized for the specified socket type.
            EAI_SOCKTYPE
                        The intended socket type was not recognized.
            EAI_SYSTEM
                        A system error occurred. The error code can be found in errno.
            EAI_OVERFLOW
                        An argument buffer overflowed.

    The following shall be declared as functions and may also be defined as macros. Function prototypes shall     be provided.

            void                   endhostent(void);
            void                   endnetent(void);
            void                   endprotoent(void);
            void                   endservent(void);
            void                   freeaddrinfo(struct addrinfo *);
            const char        *gai_strerror(int);
            int                     getaddrinfo(const char *restrict, const char *restrict,
                                      const struct addrinfo *restrict,
                                      struct addrinfo **restrict);
            struct hostent   *gethostbyaddr(const void *, socklen_t, int);
            struct hostent   *gethostbyname(const char *);
            struct hostent   *gethostent(void);
            int                      getnameinfo(const struct sockaddr *restrict, socklen_t,
                                             char *restrict, socklen_t, char *restrict,
                                             socklen_t, int);
            struct netent     *getnetbyaddr(uint32_t, int);
            struct netent     *getnetbyname(const char *);
            struct netent     *getnetent(void);
            struct protoent  *getprotobyname(const char *);
            struct protoent  *getprotobynumber(int);
            struct protoent  *getprotoent(void);
            struct servent    *getservbyname(const char *, const char *);
            struct servent    *getservbyport(int, const char *);
            struct servent    *getservent(void);
            void                     sethostent(int);
            void                     setnetent(int);
            void                     setprotoent(int);
            void                     setservent(int);


    The type socklen_t shall be defined through typedef as described in .

    Inclusion of the header may also make visible all symbols from , ,     and .

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