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Just-for-fun II

Posted on 1998-08-25
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Last Modified: 2010-04-01
int plainc(void)
{
  switch (2 //**/ 2
         ) {
    case 2: return 0; /* actually C++ */
    default: return 1; /* plain C */
   }
}

Has anybody got another function which is valid in both languages that does the same job?
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Question by:JYoungman
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LVL 11

Accepted Solution

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alexo earned 0 total points
ID: 1171175
This only works if the C compiler is strict ANSI and does not treat "//" as a valid comment delimiter (a common extension).

However, Struostrup says (B.2.1) "ISO C is being revised to allow // as in C++" thus invalidating the technique.

A similar (and more readable) technique that is guaranteed to work is:

    int plainc(void) { return sizeof('a') == sizeof(int) ? 1 : 2; }

And a slightly more obscure one:

    int plainc(void)
    {
        int x;
        {
            struct x { int a, b; };
            return sizeof(x) == sizeof(int) ? 1 : 2;
        }
    }

And the most portable is, of course:

    int plainc(void)
    {
    #ifdef __cplusplus
        return 2;
    #else
        return 1;
    #endif
    }

Do I get an 'A' ?
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LVL 11

Expert Comment

by:alexo
ID: 1171176
Did I?  It's hard to tell with 0 points ;-)
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