Returning values from a subroutine

Question

I have a batch file that I want to call subroutines within, and have them return to me an output string.

I've tried all kinds of combinations of setlocal and endlocal, different variations on % characters, and different methods: nothing has worked. I have scoured the web, but I don't think I'm searching the right things. Here is an attempt to set a global variable and change the contents pointed to by a reference, but I can't get the syntax, or maybe there's a better way. Here's my code:

echo off

for %%x in (0, 1, 15) do (
    call :hex %%x RET
    set str1=%RET%
    for /l %%y in (0, 1, 15) do (
        call :hex %%y RET
        set str2=%RET%
        echo %str1%%str2%
    )
)   
goto :eof


:hex
    set _hex=0123456789ABCDEF

    set /A len=1

    set /A offset=%1

    CALL SET s=%%_hex:~%offset%,%len%%%

    set %2=%s%
    set RET=%s%

goto :eof  

I expect the output to look like incrementing HEX numbers, but it just prints out FF's.

What is going on? How does this syntax work? How can I call a label like a c function, and have it return a value?

Answer 1

@echo off

setlocal enableDelayedExpansion
set _hex=0123456789ABCDEF
for /l %%x in (==0;1;15hex==) do (

    for /f "tokens=1,2" %%A in ("%%x 1") do set "str1=!_hex:~%%A,%%B!"

    for /l %%y in (;;0==1iterator==15;;) do (
        for /f "tokens=1,2" %%A in ("%%y 1") do set "str2=!_hex:~%%A,%%B!"
        echo !str1!!str2!
    )
)

endlocal   
goto :eof

the same logic , just removed the CALL which only will make your script slower (for further reading - http://ss64.org/viewtopic.php?id=1669 ; http://ss64.org/viewtopic.php?id=1667).

Check also the delayed expansion -> http://ss64.com/nt/delayedexpansion.html