batch file iterating sorted pairs slow -

i not using batch please forgive me if obvious. prefer not use make on 1 if have to. let's take if can fix instead:

it goes through (only) 137 .c's in folder compares modification-date .o's , recompiles if newer.

the inner for-loop name of newer file %%i variable, should not have quadratic run-time, the problem is way slow. takes 10 seconds if nothing needs recompiling, looping , sorting each pair.

for %%f in (*.c) (     /f "delims=" %%i in ('dir /b /od %%~nf.o %%~nf.c ^| more +1') (         if %%i == %%~ni.c (              rem recompile file         ) else (             rem skip         )     ) ) 

but start 137 dir /b rounds each each of 137 c-files.
, start new cmd context pipe.

i suppose it's not best way compare file times.
sort complete directory, should faster.
first sort c , o files date , create variable (cfile_<filename>) each c-file.
, each o-file clear variable.
after files remaining cfile_ variables used recompile related c-files.

the redirection 2>nul avoid error message case, when no variables begins cfile_.

@echo off setlocal enabledelayedexpansion rem remove old variables /f "delims=" %%a in ('set cfile_ 2^>nul') set "%%a="  /f "delims=" %%i in ('dir /b /od *.o *.c') (   if %%~xi==.o (     set "cfile_%%~ni="   ) else (     set cfile_%%~ni=1   ) )  /f "tokens=2* delims=_" %%c in ('set cfile_ 2^>nul') echo recompile %%c