I_love_tigersugar's blog

Silly mistake in C++
By I_love_tigersugar, history, 11 years ago, In English

The easy problem in SRM 685 is the N-th time I failed because of using __builtin_popcount instead of __builtin_popcountll. As a result, a new line has been added to my template code:

#define __builtin_popcount __builtin_popcountll

Btw, does anyone have an idea why C++ doesn't merge the 2 above functions into one to avoid such silly mistakes?

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11 years ago, hide # |
 
Vote: I like it +19 Vote: I do not like it

The reason that you have 2 different functions is that, __builtin_popcount and __builtin_popcountll are defined in C. In C, unlike C++, you don't have function overloading. For example, you can't do the following in C:

int f(int a) {
}
int f(char a) {
}

Thus, you have 2 different functions. The same happened with abs, llabs, fabs..

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    11 years ago, hide # ^ |
     
    Vote: I like it -8 Vote: I do not like it

    But abs(123.5) still returns 123.5 though. Using abs for long long also works as well.

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    11 years ago, hide # ^ |
     
    Vote: I like it +63 Vote: I do not like it

    In C, unlike C++, you don't have function overloading

    in C11 you have a special feature called "generic selection" for such cases:

    #define POPCNT(a) _Generic((a), int: __builtin_popcount(a), \  
                                long long: __builtin_popcountll(a))  

// ...

cout << POPCNT(55) << '\n';
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