Advantages of Macros

A list of the advantages of macros reads like the list of advantages for using procedures. The two mechanisms---procedure calls and macro expansion---are completely different. But the resulting effect is often similar.

• Macros hold the details of an operation in a module that can be used "as if" it were a single instruction.
• A frequently used sequence of instructions can be defined as a macro.
  • Now the macro can be used rather than retyping the sequence.
  • The sequence can be debugged just once, rather than each time it is typed in.
  • By using acual arguments, variations of the same idea are implemented.
• Macros are used to build up complex operations out of simpler operations.
• Libraries of useful macros can be created. Programmers can use these libraries without knowing much about the detailed code the macros expand into.

The above list is not complete, and most of the reasons overlap. The whole list can be summarized by saying that the advantage of macros is "modularity." Of course, "modularity" also summarizes the advantages of procedure calls, of objects, and of structured programming.

QUESTION 9:

A complicated operation has been implemented using about 1000 lines of code. The operation is expected to be used many times in a typical application program. The programmer proposes to turn the code into a macro and put it in a macro library. Is this a good idea?

ANSWERS:

1. No---expanded source files using the macro will get too large.
2. No---since the macro is large it should not be placed in a library.
3. Yes--users will not want to see the details, so the modularity of a macro is a good idea.
4. Yes--once it is in a library all programmers can use it.