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C:getaddrinfo

lastmod 2020-03-31created 2019-09-093 edits

Example 

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

int main(int argc,char *argv[])
{
    int status;
    struct addrinfo hints;
    struct addrinfo *servinfo; // 결과를 저장할 변수
    memset(&hints, 0, sizeof(hints)); // hints 구조체의 모든 값을 0으로 초기화
    hints.ai_family = AF_UNSPEC; // IPv4와 IPv6 상관하지 않고 결과를 모두 받겠다
    hints.ai_socktype = SOCK_STREAM; // TCP stream sockets
    status = getaddrinfo("www.google.com", "80", &hints, &servinfo);

    return 0;
}

Result

The getaddrinfo function dynamically allocates the memory for all the structures that result points to. The caller of the getaddrinfo function uses those structures and is responsible for freeing the memory. To free the memory of the addrinfo list, you must call the freeaddrinfo function.

FILES

  • /etc/hosts
  • /etc/host.conf
  • /etc/resolv.conf
  • /etc/gai.conf

Return value

This function returns 0 on success. On failure it returns a nonzero value, one of the error values below.

EAI_ADDRFAMILY
The specified network host has no addresses in the requested address family. For example, if you ask a network host that has only IPv4 addresses to "give me an IPv6 address," this error is returned.
EAI_AGAIN
The nameserver returned a temporary failure indication. It means to try again after some time.
EAI_BADFLAGS
hints.ai_flags contains invalid flags. Or hints.ai_flags included AI_CANONNAME and the name was NULL.
EAI_FAIL
The nameserver returned a permanent failure indication. Unlike EAI_AGAIN, it means that retrying will fail too.
EAI_FAMILY
The requested address family is not supported.
EAI_MEMORY
Not enough memory to perform getaddrinfo. This is pretty much a hopeless situation. Wait, hoping the kernel's OOM killer does its job, retry after some time, and if you still get the same error, just reboot and be done with it.
EAI_NODATA
The specified network host exists... but has no network addresses defined.
EAI_NONAME
The node or service is not known. Or both node and service are NULL. Or AI_NUMERICSERV was specified in hints.ai_flags, but service was not a numeric string representing a port number. In any case, it means the input parameters were wrong. Did you pass the parameters correctly? Check your own code again.
EAI_SERVICE
The requested service is not available for the requested socket type. It may be available through another socket type. For example, this error can occur if service is "shell" (a service available only on stream sockets) and hints.ai_protocol is IPPROTO_UDP or hints.ai_socktype is SOCK_DGRAM. Or the error can occur if service is not NULL and hints.ai_socktype is SOCK_RAW (a socket type that does not support the concept of services).
EAI_SOCKTYPE
The requested socket type is not supported. For example, when hints.ai_socktype and hints.ai_protocol are inconsistent. This error can occur if you pass as the input parameter a hint with SOCK_DGRAM in ai_socktype and IPPROTO_TCP in ai_protocol.
EAI_SYSTEM
Some other system error not covered by any of the above, a troublesome case. You need to check errno for details.

To interpret the return value: 

const char *gai_strerror(int errcode);

This function converts the error code returned by getaddrinfo( ) into a human-readable string. Useful for debugging and log output, so keep it in mind.

Troubleshooting

EAI_SERVICE

The requested service is not available for the requested socket type. Service names are things like https, smtp, and ftp. The code that looks this up can be found here. If you check where the servname variable is used, you can see that partway through it looks it up using getservbyname.

This function checks the contents of the /etc/services file. If this file does not exist, you need to create it. On Debian, you can add it with the command below. 

$ sudo apt-get install netbase

See also

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