Pass a pointer to a zero terminated string as parameter. It specifies that the
FTP transfer will be made actively and the given string will be used to get
the IP address to use for the FTP PORT instruction.
The PORT instruction tells the remote server to connect to our specified IP
address. The string may be a plain IP address, a host name, a network
interface name (under Unix) or just a - symbol to let the library use your
systems default IP address. Default FTP operations are passive, and thus
wont use PORT.
The address can be followed by a : to specify a port, optionally followed by
a - to specify a port range. If the port specified is 0, the operating
system will pick a free port. If a range is provided and all ports in the
range are not available, libcurl will report CURLE_FTP_PORT_FAILED for the
handle. Invalid port/range settings are ignored. IPv6 addresses followed by
a port or portrange have to be in brackets. IPv6 addresses without port/range
specifier can be in brackets.
Examples with specified ports:
You disable PORT again and go back to using the passive version by setting
this option to NULL.