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gethostbyname function

The gethostbyname function retrieves host information corresponding to a host name from a host database.

Note  The gethostbyname function has been deprecated by the introduction of the getaddrinfo function. Developers creating Windows Sockets 2 applications are urged to use the getaddrinfo function instead of gethostbyname.

Syntax


struct hostent* FAR gethostbyname(
  _In_  const char *name
);

Parameters

name [in]

A pointer to the null-terminated name of the host to resolve.

Return value

If no error occurs, gethostbyname returns a pointer to the hostent structure described above. Otherwise, it returns a null pointer and a specific error number can be retrieved by calling WSAGetLastError.

Error codeMeaning
WSANOTINITIALISED

A successful WSAStartup call must occur before using this function.

WSAENETDOWN

The network subsystem has failed.

WSAHOST_NOT_FOUND

Authoritative answer host not found.

WSATRY_AGAIN

Nonauthoritative host not found, or server failure.

WSANO_RECOVERY

A nonrecoverable error occurred.

WSANO_DATA

The requested name is valid, but no data of the requested type was found. This error is also returned if the name parameter contains a string representation of an IPv6 address or an illegal IPv4 address.

This error should not be interpreted to mean that the name parameter contains a name string that has been validated for a particular protocol (an IP hostname, for example). Since Winsock supports multiple name service providers, a name may potentially be valid for one provider and not accepted by another provider.

WSAEINPROGRESS

A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.

WSAEFAULT

The name parameter is not a valid part of the user address space.

WSAEINTR

A blocking Windows Socket 1.1 call was canceled through WSACancelBlockingCall.

 

Remarks

The gethostbyname function returns a pointer to a hostent structure—a structure allocated by Windows Sockets. The hostent structure contains the results of a successful search for the host specified in the name parameter.

If the host specified in the name parameter has both IPv4 and IPv6 addresses, only the IPv4 addresses will be returned. The gethostbyname function can only return IPv4 addresses for the name parameter. The getaddrinfo function and associated addrinfo structure should be used if IPv6 addresses for the host are required or if both IPv4 and IPv6 addresses for the host are required.

If the name parameter points to an empty string or name is NULL, the returned string is the same as the string returned by a successful gethostname function call (the standard host name for the local computer).

If the name parameter contains a string representation of a legal IPv4 address, then the binary IPv4 address that represents the string is returned in the hostent structure. The h_name member of the hostent structure contains the string representation of the IPv4 address and the h_addr_list contains the binary IPv4 address. If the name parameter contains a string representation of an IPv6 address or an illegal IPv4 address, then the gethostbyname function will fail and return WSANO_DATA.

The memory for the hostent structure returned by the gethostbyname function is allocated internally by the Winsock DLL from thread local storage. Only a single hostent structure is allocated and used, no matter how many times the gethostbyaddr or gethostbyname functions are called on the thread. The returned hostent structure must be copied to an application buffer if additional calls are to be made to the gethostbyname or gethostbyaddr functions on the same thread. Otherwise, the return value will be overwritten by subsequent gethostbyname or gethostbyaddr calls on the same thread. The internal memory allocated for the returned hostent structure is released by the Winsock DLL when the thread exits.

An application should not try to release the memory used by the returned hostent structure. The application must never attempt to modify this structure or to free any of its components. Furthermore, only one copy of this structure is allocated per thread, so the application should copy any information it needs before issuing any other function calls to gethostbyname or gethostbyaddr .

The gethostbyname function cannot take an IP address string as a parameter passed to it in the name and resolve it to a host name. Such a request is treated exactly as a string representation of an IPv4 address or an unknown host name were passed. An application can use the inet_addr to convert an IPv4 address string to a binary IPv4 address, then use another function, gethostbyaddr, to resolve the IPv4 address to a host name.

Note  The gethostbyname function does not check the size of the name parameter before passing the buffer. With an improperly sized name parameter, heap corruption can occur.

Example Code

The following examples demonstrates the use of the gethostbyname function.


#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <windows.h>
#pragma comment(lib, "ws2_32.lib")

int main(int argc, char **argv)
{

    //-----------------------------------------
    // Declare and initialize variables
    WSADATA wsaData;
    int iResult;

    DWORD dwError;
    int i = 0;

    struct hostent *remoteHost;
    char *host_name;
    struct in_addr addr;

    char **pAlias;

    // Validate the parameters
    if (argc != 2) {
        printf("usage: %s hostname\n", argv[0]);
        printf("  to return the IP addresses for the host\n");
        printf("       %s www.contoso.com\n", argv[0]);
        printf(" or\n");
        printf("       %s IPv4string\n", argv[0]);
        printf("  to return an IPv4 binary address for an IPv4string\n");
        printf("       %s 127.0.0.1\n", argv[0]);
        return 1;
    }
    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed: %d\n", iResult);
        return 1;
    }

    host_name = argv[1];

    printf("Calling gethostbyname with %s\n", host_name);
    remoteHost = gethostbyname(host_name);
    
    if (remoteHost == NULL) {
        dwError = WSAGetLastError();
        if (dwError != 0) {
            if (dwError == WSAHOST_NOT_FOUND) {
                printf("Host not found\n");
                return 1;
            } else if (dwError == WSANO_DATA) {
                printf("No data record found\n");
                return 1;
            } else {
                printf("Function failed with error: %ld\n", dwError);
                return 1;
            }
        }
    } else {
        printf("Function returned:\n");
        printf("\tOfficial name: %s\n", remoteHost->h_name);
        for (pAlias = remoteHost->h_aliases; *pAlias != 0; pAlias++) {
            printf("\tAlternate name #%d: %s\n", ++i, *pAlias);
        }
        printf("\tAddress type: ");
        switch (remoteHost->h_addrtype) {
        case AF_INET:
            printf("AF_INET\n");
            break;
        case AF_NETBIOS:
            printf("AF_NETBIOS\n");
            break;
        default:
            printf(" %d\n", remoteHost->h_addrtype);
            break;
        }
        printf("\tAddress length: %d\n", remoteHost->h_length);

        i = 0;
        if (remoteHost->h_addrtype == AF_INET)
        {
            while (remoteHost->h_addr_list[i] != 0) {
                addr.s_addr = *(u_long *) remoteHost->h_addr_list[i++];
                printf("\tIP Address #%d: %s\n", i, inet_ntoa(addr));
            }
        }
        else if (remoteHost->h_addrtype == AF_NETBIOS)
        {   
            printf("NETBIOS address was returned\n");
        }   
    }

    return 0;
}


Windows Phone 8: This function is supported for Windows Phone Store apps on Windows Phone 8 and later.

Windows 8.1 and Windows Server 2012 R2: This function is supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and later.

Requirements

Minimum supported client

Windows 8.1, Windows Vista [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Minimum supported phone

Windows Phone 8

Header

Winsock2.h

Library

Ws2_32.lib

DLL

Ws2_32.dll

See also

Winsock Reference
Winsock Functions
addrinfo
addrinfoW
getaddrinfo
GetAddrInfoEx
GetAddrInfoW
gethostbyaddr
gethostname
inet_addr
WSAAsyncGetHostByName
hostent

 

 

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