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Editorial Team
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Asked: 2026-05-27T20:17:54+00:00

I was wondering … When you make a change to either file1.c or file2.c

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I was wondering …

When you make a change to either file1.c or file2.c or file1.h, the following makefile recompiles only what’s needed (which is nice)

# Link to executable
result: file1.o file2.o
    gcc file1.o file2.o -o result23

# Assemble to .o object files
file1.o:    file1.s
    gcc -c dist/file1.s

file2.o:    file2.s
    gcc -c dist/file2.s

# Compile to .s assembly files
file1.s:    file1.c
    gcc -S file1.c

file2.s:    file2.c
    gcc -S file2.c

When I move built object to another directory, however, everything is rebuilt at all times, regardless whether only 1 file’s content was changed.

# Link to executable
result: file1.o file2.o
    gcc file1.o file2.o -o result23

# Assemble to .o object files
file1.o:    file1.s
    gcc -c dist/file1.s
    mv file1.o dist

file2.o:    file2.s
    gcc -c dist/file2.s
    mv file2.o dist

# Compile to .s assembly files
file1.s:    file1.c
    gcc -S file1.c
    mv file1.s dist

file2.s:    file2.c
    gcc -S file2.c
    mv file2.s dist

It seems that this is happening because make does not know where the .o files are in it’s environment.

With this a few questions:

  • Can make have access to environment variables? If so, could you provide an example?
  • Can make be made aware of incremental builds when distribution directory is different from current directory?
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1 Answer

  1. Editorial Team

    To fix your build you’ll need to do something like this:

    # Link to executable
result: dist/file1.o dist/file2.o
    gcc dist/file1.o dist/file2.o -o result

# Assemble to .o object files in main directory
dist/file1.o:    dist/file1.s
    gcc -c dist/file1.s -o dist/file1.o

dist/file2.o:    dist/file2.s
    gcc -c dist/file2.s -o dist/file2.o

# Compile to .s assembly files
dist/file1.s:    file1.c
    gcc -S file1.c -o dist/file1.s

dist/file2.s:    file2.c
    gcc -S file2.c -o dist/file2.s

    You can certainly use environment variables in make too.. though I’m not sure how that relates to the core of your question: Just use something like this, set BUILDDIR and OBJDIR and have a makefile like this:

    $(BUILDDIR)/foo : $(OBJDIR)/bar.o
   g++ $(OBJDIR)/bar.o -o $(BUILDDIR)/foo

    Though you can make this (and my fixed makefile too) nicer using automatic variables:

    $(BUILDDIR)/foo : $(OBJDIR)/bar.o
  g++ $? -o $@
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