The HostFile property is used to specify the name of an
alternate file for resolving hostnames and IP addresses. The host
file is used as a database that maps an IP address to one or more
hostnames, and is used when setting the HostName or
HostAddress properties and establishing a connection with a
remote host. The file is a plain text file, with each line in the
file specifying a record, and each field separated by spaces or tabs.
The format of the file must be as follows:
ipaddress hostname [hostalias ...]
For example, one typical entry maps the name "localhost"
to the local loopback IP address. This would be entered as:
127.0.0.1 localhost
The hash character (#) may be used to specify a comment in the
file, and all characters after it are ignored up to the end of the
line. Blank lines are ignored, as are any lines which do not follow
the required format.
Setting this property loads the file into memory allocated for the
current thread. If the contents of the file have changed after the
function has been called, those changes will not be reflected when
resolving hostnames or addresses. To reload the host file from disk,
set the property again with the same file name. To remove the
alternate host file from memory, specify an empty string as the file
name.
If a host file has been specified, it is processed before the
default host file when resolving a hostname into an IP address, or an
IP address into a hostname. If the host name or address is not found,
or no host file has been specified, a nameserver lookup is
performed.
Because the alternate host file is cached for the current thread,
setting this property will affect all instances of the control in the
same thread. For example, if a project has three instances of the
control loaded on a form, setting the HostFile property will
affect all three controls, not just the control that set the
property. To determine if an alternate host file has been cached,
check the property value. If the property returns an empty string, no
alternate host file has been cached.