Select Case

FreeBASIC

previous page next page

Select Case

Basic implementation

dim i as integer		dim i as integer

				scope
select case i + 123			dim temp as integer = any
					temp = i + 123

case 1					if( temp

 1 ) then goto cmplabel1
					scope
	print "1"				print "1"
					end scope
					goto endlabel

case 2					cmplabel1:
					if( temp

 2 ) then goto cmplabel2
					scope
	print "2"				print "2"
					end scope
					goto endlabel

case else				cmplabel2:
					scope
	print "else"				print "else"
					end scope

end select				cmplabel3:    '' unused only because in this example the last CASE is not conditional
					endlabel:
				end scope

SELECT CASE
- opens the implicit outer scope
- declares the temp var
  - when inside a procedure with STATIC, the temp var will be made STATIC
  - the FB_SYMBATTRIB_TEMP is removed from the temp var, because it lives longer than just one statement
- emits the assignment
- declares the end label
each CASE
- if there was a previous CASE
  - closes the previous CASE's scope
  - emits a jump to the end label
- emits the label for this CASE
- emits a conditional branch that jumps to the next CASE if the CASE condition is not met
- opens the CASE's scope
- CASE ELSE does not emit a conditional branch
- once CASE ELSE was used, no further CASE blocks are allowed
END SELECT
- closes the previous CASE's scope
- emits an extra CASE label at the end (There is no CASE coming anymore, but this allows the last CASE to jump to the end, if it is a conditional CASE. The last CASE could jump to the SELECT's end label instead, but that would require some special case handling code.)
- emits the end label
any EXIT SELECTs jump immediately to the end label

SELECT CASE on strings/zstrings/fixstrs

dim s as string			dim s as string

				scope
select case s + "1"			dim temp as string

					fb_StrAssign( temp, s )
					fb_StrConcatAssign( temp, "1" )

case "1"				if( fb_StrCompare( temp, "1" )

 0 ) then goto cmplabel1
					scope
	print "1"				print "1"
					end scope
					goto endlabel

					cmplabel1:
end select				endlabel:
					fb_StrDelete( temp )    '' destroying the temp var at scope end
				end scope

				fb_StrDelete( s )

SELECT CASE on string/zstring/fixstr expressions uses a string temp var
- probably because that's easiest
- knowing the string length will potentially speed up the following comparisons
- the dynamic memory allocation can be a slow down too
the string temp var is destroyed at scope end or scope breaks (e.g. reaching END SELECT, or EXIT FUNCTION from within a CASE block)

SELECT CASE on wstrings

dim w as wstring * 10			dim w as wstring * 10

					scope
select case w + wstr( "1" )			dim temp as wstring ptr

						dim tempexpr as wstring ptr = w + wstr( "1" )
						temp = fb_WstrAlloc( fb_WstrLen( tempexpr ) )
						fb_WstrAssign( temp, tempexpr )

case wstr( "1" )				if( fb_WstrCompare( temp, wstr( "1" ) )

 0 ) then goto cmplabel1
						scope
	print "1"					print "1"
						end scope
						goto endlabel

						cmplabel1:
end select					endlabel:
						fb_WstrDelete( temp )    '' destroying the temp var at scope end
					end scope

similar to SELECT CASE on zstrings, for wstring expressions a wstring is dynamically allocated
the temp wstring is treated much like a dynamic wstring object would be
- it is a VAR symbol with type WCHAR PTR
- marked with FB_SYMBSTATS_WSTRING
- this allows ctor/dtor checks to recognize it and give it the needed treatment
this way, the temp wstring is destroyed at scope end or scope breaks

SELECT CASE without temp var

When the expression given to the select statement is just a simple variable access, then no temporary variable needs to be created. In this case, the given variable itself will be used in the comparisons at each case statement. For example:

dim i as integer		dim i as integer

				scope
select case i

case 1					if( i

 1 ) then goto cmplabel1
					scope
	print "1"				print "1"
					end scope
					goto endlabel

end select				cmplabel1:
					endlabel:
				end scope

previous page start next page