Comparison of User-Defined Function Features

The following table illustrates the similarities and differences between regular user-defined functions (non-library) and library user-defined functions.

Quality	Normal User Defined Function	User Defined Library Function in Main Program	User Defined Library Function in Separate Program
			Resident	Present	As Needed
LIBRARY keyword required on DEF statement	no	yes	yes	yes	yes
Linkage must be established (via LIBRARY statement) before function may be called	no	yes	yes	yes	yes
Program may be specified in named LIBRARY statement	n/a	no	yes	yes	yes
Loaded program will be searched for function when unnamed LIBRARY statement is executed	n/a	yes	yes	yes	no
Main program's global variables are available to the function	no	yes	no	no	no
Point at which global variables are cleared	When main program ends	When main program ends	When main program ends (Default). Other options available	When main program ends	When function call ends
Using OPTION RETAIN in the library program causes the library to retain global variables irrespective of when the program ends	n/a	na/a	yes	no	no
Library is loaded into memory with the LOAD command	n/a	n/a	yes	no	no
Library is cleared from memory with the CLEAR command	n/a	n/a	yes	no	no
Library is automatically removed from memory when all function definitions are reassigned	n/a	n/a	no	yes	n/a
Library is automatically removed from memory when main program ends	n/a	n/a	no	yes	n/a