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    <p>What we need here is two (or more) versions of <code>c.o</code>, compiled with different flags and to be linked into different executables. You could do this with contrived filenames like <code>c_for_a.o</code>, but it's tidier to keep them in different directories, <code>for_a/</code> and <code>for_b/</code>:</p> <pre><code>a for_a/%: CFLAGS = a: a.o for_a/c.o b for_b/%: CFLAGS = -mno-cygwin b: b.o for_b/c.o </code></pre> <p>(If this isn't clear I can fill in the rest of the Makefile.)</p> <p><b>EDIT:</b><br> If you don't want to keep multiple <code>c.o</code>'s, you will have to recompile c.o sometimes. There is a small improvement possible on the <code>checkTarget</code> idea.</p> <p>When you are building a target like <code>b</code>, and <code>c.o</code> already exists, it matters whether that <code>c.o</code> was built with the <code>CFLAGS</code> suited to <code>b</code>, and you use <code>checkTarget</code> to record that information. <em>But you don't care what <code>CFLAGS</code> were used, only whether they were <code>b</code>'s <code>CFLAGS</code></em>. So you don't have to record anything in the <code>checkTarget</code> file, just update it when you build a new target:</p> <pre><code>a: CFLAGS = b: CFLAGS = -mno-cygwin # You may be able to combine the a and b rules... a: a.o c.o checkTarget # build c.o touch checkTarget # build the target b: b.o c.o checkTarget # build c.o touch checkTarget # build the target # Need this to create checkTarget the first time checkTarget: @touch $@ </code></pre>
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    1. POHow to ensure object files are compiled with correct settings in Makefile with multiple MAKE targets
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    1. COGood answer. If the project is large, say 50 object files, this would work if the number of files to recompile (c.c in the example) is small. If the majority would require recompilation, this strategy would become clumsy I think. Any ideas for that scenario?
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    2. CO@Thomas Nilsson: it depends on what you're trying to optimize. If you don't want to recompile `c.c` more than you must, then you must keep different versions of it, and this is the best way. If you don't want to keep multiple `c.o`'s, but you want to recompile `c.o` only when you must, there's another way, a slight improvement on your checkTarget. I'll edit my answer to include it.
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    3. COHmmm, if I understand correctly, checkTarget is a timestamp so that e.g. if you build b but b.o and c.o exists, checkTarget will still trigger the build rule. Then in the commands you are hardwiring the build of c.o according to the CFLAGS. If this is your intention, I'm not fully satisfied (but then again that might not be possible ;-), because I would constantly have to update the explicit build commands as my requirements changed. I was hoping for some way to make every %.o dependent on the CFLAGS used to compile it, and a compile triggered only if the CFLAGS was not the same.
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