Description: The question is: When localizing a function via SETLOCAL and ENDLOCAL, how to return a value that was calculated before executing ENDLOCAL when ENDLOCAL restores all variables back to its original state?
The answer comes with "variable expansion". The command processor expands all variables of a command before executing the command. Letting the command processor executing ENDLOCAL and a SET command at once solves the problem. Commands can be grouped within brackets.
Script:
@echo off
set "aStr=Expect no changed, even if used in function"
set "var1=Expect changed"
echo.aStr before: %aStr%
echo.var1 before: %var1%
call:myGetFunc var1
echo.aStr after : %aStr%
echo.var1 after : %var1%
echo.&pause&goto:eof
::--------------------------------------------------------
::-- Function section starts below here
::--------------------------------------------------------
:myGetFunc - passing a variable by reference
SETLOCAL
set "aStr=DosTips"
( ENDLOCAL
set "%~1=%aStr%"
)
goto:eof
:myGetFunc2 - passing a variable by reference
SETLOCAL
set "aStr=DosTips"
ENDLOCAL&set "%~1=%aStr%" &rem THIS ALSO WORKS FINE
goto:eof
Script Output: Script Output
aStr before: Expect no changed, even if used in function
var1 before: Expect changed
aStr after : Expect no changed, even if used in function
var1 after : DosTips
Press any key to continue . . .
Recursive Functions - Tadaaah!!!
Description: Being able to completely encapsulate the body of a function by keeping variable changes local to the function and invisible to the caller we are now able to call a function recursively making sure each level of recursion works with its own set of variables even thought variable names are being reused.
Example: The next example below shows how to calculate a Fibonacci number recursively. The recursion ss when the Fibonacci algorism reaches a number greater or equal to a given input number.
The example starts with the numbers 0 and 1 the :myFibo function calls itself recursively to calculate the next Fibonacci number until it finds the Fibonacci number greater or equal 1000000000.
The first argument of the myFibo function is the name of the variable to store the output in. This variable must be initialized to the Fibonacci number to start with and will be used as current Fibonacci number when calling the function and will be set to the subsequent Fibonacci number when the function returns.
Script:
@echo off
set "fst=0"
set "fib=1"
set "limit=1000000000"
call:myFibo fib,%fst%,%limit%
echo.The next Fibonacci number greater or equal %limit% is %fib%.
echo.&pause&goto:eof
