Chapter 5. Answers to Exercises
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## Chapter 5. Answers to Exercises

## Exercise 3.1

This is something of a trick question, for which I apologize. The trick comes from the UNIX® definition of a suffix, which PMake does not necessarily share. You will have noticed that all the suffixes used in this tutorial (and in UNIX® in general) begin with a period (`.ms`, `.c`, etc.). Now, PMake's idea of a suffix is more like English's: it is the characters at the end of a word. With this in mind, one possible solution to this problem goes as follows:

.SUFFIXES : ec.exe .exe ec.obj .obj .asm ec.objec.exe .obj.exe : link -o $(.TARGET) $(.IMPSRC) .asmec.obj : asm -o $(.TARGET) -DDO_ERROR_CHECKING $(.IMPSRC) .asm.obj : asm -o $(.TARGET) $(.IMPSRC)

## Excercise 3.2

The trick to this one lies in the `:=` variable-assignment operator and the `:S` variable-expansion modifier. Basically what you want is to take the pointer variable, so to speak, and transform it into an invocation of the variable at which it points. You might try something like:

$(PTR:S/^/\$(/:S/$/))

which places `$(` at the front of the variable name and `)` at the end, thus transforming `VAR,` for example, into `$(VAR)`, which is just what we want. Unfortunately (as you know if you have tried it), since, as it says in the hint, PMake does no further substitution on the result of a modified expansion, that is all you get. The solution is to make use of `:=` to place that string into yet another variable, then invoke the other variable directly:

*PTR := $(PTR:S/^/\$(/:S/$/)/)

You can then use `$(*PTR)` to your heart's content.

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