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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Passing values from structure arrays to a generic geometrical mean function
Date: Sat, 28 Jan 2017 11:02:05 -0800
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Alla _ <modelling.data@gmail.com> writes:
> On Friday, January 27, 2017 at 10:48:29 PM UTC+3, Keith Thompson wrote:
[...]
>> You could also wrap the entire function definition in a macro
>> definition, with macro parameters to specify the name of the structure
>> type and of the double member.  You'd have to invoke the macro for each
>> structure type, creating a new function with a distinct name.
>> 
> Do I include this macro as part of the function definition (as a parameter),
> and then use specific struct types within a calling routine to pass those
> to a function?

No, the idea is that the macro would expand to an entire function
definition, and you'd invoke the macro once for each structure type to
define a function for that type.  It's very similar to a C++ template,
but much uglier and less type-safe.

Here's a trivial (and not at all useful) example of what I'm talking
about:

    #include <stdio.h>
    
    #define DEFINE_INCREMENT_FUNCTION(type, name) \
        void name(type *ptr) { \
            *ptr ++; \
        }
    
    DEFINE_INCREMENT_FUNCTION(int, inc_int)
    DEFINE_INCREMENT_FUNCTION(double, inc_double)
    
    int main(void) {
        int i = 3;
        inc_int(&i);
        double d = 4.5;
        inc_double(&d);
        printf("i = %d, d = %f\n", i, d);
    }

This is not a good idea.  This is an ugly approach that might become
necessary in some circumstances.

A similar approach is to define the function in a separate source file,
and have the definition refer to several macros; you could then define
those macros and #include the file.

Note carefully that I am *not* recommending either approach.  I'm just
presenting alternatives that might become necessary if you need to deal
with an existing set of data structures that don't allow for more
straighforward code.

[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"