CODEWITHSUNDEEP
cfunctioncross-platform
Jay Chung
Jay Chung

Reputation: 175

using #ifdef for different number of function argument depending on platforms

I have a requirement that states a function should take in one new argument at the beginning of the argument list for a new platform I am working on.

so the following would be a prototype for this new platform

void foo (int newarg, const char * a, int b, int c);

where as in the previous case it was just

void foo (const char * a, int b, int c);

My concern is readability and code space . So I am thinking of using ifdefs but i am not sure if it is a good idea to use if def with in a argument list.

1) 

void foo (
#ifdef __NEWPLATFORM__
    int newarg, 
#else
    const char * a, int b, int c
#endif
);

or

#if __NEWPALTFORM__
    void foo (int newarg, const char * a, int b, int c);
#else
    void foo (const char * a, int b, int c);
#endif

Btw I cannot put the new argument to the end of the list which would make it a lot easier.

Which one of the two (or maybe a better solution) is better?

Thanks

Upvotes: 1

Views: 2137

Answers (2)

Will
Will

Reputation: 921

A third option would be to conditionally define a symbol for the extra argument. You might use the #ifdef section to include other useful platform related stuff, for example:

#ifdef MY_NEW_PLATFORM
 #define EXTRA_ARGS int newarg,
 #define GET_EXTRA newarg
 #define SET_EXTRA(val) newarg = (val)
#else
 #define EXTRA_ARGS
 #define GET_EXTRA 0
 #define SET_EXTRA(val)
#endif

...

void foo (EXTRA_ARGS const char * a, int b, int c) {
  b = GET_EXTRA + c;  /* Just as example */
  SET_EXTRA(b+c);
}

As you can see, the foo function has no distracting "#ifdefs", and it compiles in any platform.

Upvotes: 1

Keith Nicholas
Keith Nicholas

Reputation: 44306

Given that you are changing all the calls to foo,

just change foo to the function with more parameters, then #ifdef internal to the function for different functionality.

void foo (int newarg, const char * a, int b, int c){
   #ifdef __NEWPALTFORM__
   #else
   #endif
}

Also worth considering whether the parameters to the function should really be a struct, in which case new parameters in the future won't be much of an issue. Not enough context in your question to say whether this is a good idea or not

but it would be something like :=

typedef struct {
   int newarg;
   const char* a;
   int b;
   int c;
} fooType;

    void foo(fooType f)   // either by value or by pointer depending on context
    {
      // #ifdefs...
    }

Upvotes: 2

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