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Thinking in C++
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Default targets

After the macros and suffix rules, make looks for the first “target” in a file, and builds that, unless you specify differently. So for the following makefile:

CPP = mycompiler
.SUFFIXES: .exe .cpp
        $(CPP) $<

If you just type ‘make’, then target1.exe will be built (using the default suffix rule) because that’s the first target that make encounters. To build target2.exe you’d have to explicitly say ‘make target2.exe’. This becomes tedious, so you normally create a default “dummy” target that depends on all the rest of the targets, like this:

CPP = mycompiler
.SUFFIXES: .exe .cpp
        $(CPP) $<
all: target1.exe target2.exe

Here, ‘all’ does not exist and there’s no file called ‘all’, so every time you type make, the program sees ‘all’ as the first target in the list (and thus the default target), then it sees that ‘all’ does not exist so it had better make it by checking all the dependencies. So it looks at target1.exe and (using the suffix rule) sees whether (1) target1.exe exists and (2) whether target1.cpp is more recent than target1.exe, and if so runs the suffix rule (if you provide an explicit rule for a particular target, that rule is used instead). Then it moves on to the next file in the default target list. Thus, by creating a default target list (typically called ‘all’ by convention, but you can call it anything) you can cause every executable in your project to be made simply by typing ‘make’. In addition, you can have other non-default target lists that do other things – for example, you could set it up so that typing ‘make debug’ rebuilds all your files with debugging wired in.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire