This is an old revision of the document!
by Jon Ripley, January 2006
BBC BASIC for Windows provides no built in function to check whether a library has been loaded into memory using the INSTALL command.
The following routine FN_IsInstalled(lib$) implements a method to check if a library is currently INSTALLed:
DEF FN_IsInstalled(lib$) IF ?HIMEM = 0 THEN = FALSE LOCAL P%, tmp$ SYS "CharUpperBuff", !^lib$, LEN lib$ IF RIGHT$(lib$,4) = ".BBC" THEN lib$ = LEFT$(lib$, LEN lib$ - 4) P% = HIMEM REPEAT tmp$ = $$(P%+4) IF lib$ = "-" THEN PRINT tmp$ SYS "CharUpperBuff", !^tmp$, LEN tmp$ IF lib$ = tmp$ OR tmp$ = lib$ + ".BBC" THEN = TRUE P% += ?P% WHILE ?P% AND ?P% < &FF P% += ?P% ENDWHILE UNTIL (!P% AND &FFFFFF) = &FFFF00 = FALSE
To check if a library is installed use code similar to the following:
IF FN_IsInstalled(@lib$+"WINLIB") THEN PRINT "WINLIB is installed." ELSE PRINT "WINLIB is not installed." ENDIF
To list all installed libraries call FN_IsInstalled(“-”).
When you INSTALL a library, BBC BASIC for Windows checks whether that library is already installed (version 5.91a or later only), however it performs a case-sensitive comparison of the supplied path/filename. It will reliably detect the same INSTALL statement being executed a second time, but not necessarily a different INSTALL statement which installs the same library but specifies it differently.
Installing a library more than once is safe but wastes memory. If this is a concern, the following routine can be used instead of INSTALL:
DEF PROC_InstallOnce(lib$) IF NOT FN_IsInstalled(lib$) THEN INSTALL lib$ ENDPROC