The install Handle
Go Up to About the InterBase Install API
Each install instance has a unique handle that identifies it. This handle is a variable of type OPTION_HANDLE (see Data Types Defined for the Install API) that you initialize to zero at the beginning of the InterBase install. Throughout this chapter, this variable is referred to as handle, and its address is phandle. Once you have passed it to isc_install_set_option(), it references a data area where all the options for the current install are stored. You need not and should not de-reference handle directly. The install data is all maintained by the install engine. You need only pass handle or a pointer to it, depending on the syntax of the function you are calling.
You must pass handle to isc_install_set_option() before passing it to any of the other functions, since isc_install_set_option() is the only function that accepts handle when its value is zero. The others return an error.