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 code | Meaning |
|---|
- 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 getaddrinfo function and associated addrinfo structure should be used if both IPv4 and IPv6 addresses for the host are required.
If the name parameter contains a string representation of a legal IPv4 address, then the IPv4 address 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 resolve IP address strings passed to it. Such a request is treated exactly as if an unknown host name were passed. Use
inet_addr to convert an IP address string to an actual IPv4 address, then use another function,
gethostbyaddr, to obtain the contents of the
hostent structure.
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).
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, "wininet.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_INET6:
printf("AF_INET6\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_INET6)
{
printf("IPv6 address was returned\n");
}
}
return 0;
}
Requirements
| Minimum supported client | Windows 2000 Professional |
|---|
| Minimum supported server | Windows 2000 Server |
|---|
| Header | Winsock2.h |
|---|
| Library | Ws2_32.lib |
|---|
| DLL | Ws2_32.dll |
|---|
See Also
- Winsock Reference
- Winsock Functions
- addrinfo
- addrinfoW
- getaddrinfo
- GetAddrInfoEx
- GetAddrInfoW
- gethostbyaddr
- gethostname
- WSAAsyncGetHostByName
- hostent
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Build date: 1/28/2010