In the above example a macro was used to calculate the area of the circle. As we know, even a function can be written to calculate the area of the circle. Though macro calls are ‘like’ function calls, they are not really the same things. Then what is the difference between the two?
In a macro call the preprocessor replaces the macro template with its macro expansion, in a stupid, unthinking, literal way. As against this, in a function call the control is passed to a function along with certain arguments, some calculations are performed in the function and a useful value is returned back from the function.
This brings us to a question: when is it best to use macros with arguments and when is it better to use a function? Usually macros make the program run faster but increase the program size, whereas functions make the program smaller and compact.
If we use a macro hundred times in a program, the macro expansion goes into our source code at hundred different places, thus increasing the program size. On the other hand, if a function is used, then even if it is called from hundred different places in the program, it would take the same amount of space in the program.
But passing arguments to a function and getting back the returned value does take time and would therefore slow down the program. This gets avoided with macros since they have already been expanded and placed in the source code before compilation.
Moral of the story is—if the macro is simple and sweet like in our examples, it makes nice shorthand and avoids the overheads associated with function calls. On the other hand, if we have a fairly large macro and it is used fairly often, perhaps we ought to replace it with a function.
In a macro call the preprocessor replaces the macro template with its macro expansion, in a stupid, unthinking, literal way. As against this, in a function call the control is passed to a function along with certain arguments, some calculations are performed in the function and a useful value is returned back from the function.
This brings us to a question: when is it best to use macros with arguments and when is it better to use a function? Usually macros make the program run faster but increase the program size, whereas functions make the program smaller and compact.
If we use a macro hundred times in a program, the macro expansion goes into our source code at hundred different places, thus increasing the program size. On the other hand, if a function is used, then even if it is called from hundred different places in the program, it would take the same amount of space in the program.
But passing arguments to a function and getting back the returned value does take time and would therefore slow down the program. This gets avoided with macros since they have already been expanded and placed in the source code before compilation.
Moral of the story is—if the macro is simple and sweet like in our examples, it makes nice shorthand and avoids the overheads associated with function calls. On the other hand, if we have a fairly large macro and it is used fairly often, perhaps we ought to replace it with a function.
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