fabs vs. fabsl, should I ever have to type fabsl in my source?

Question

I'm rewriting some Mac code that embeds a freeware library originally written in C. The compiler is complaining that since I'm using long double, I should use fabsl rather than fabs. So I went and changed them.

However, reading a few pages on the topic it seems that there should be no difference, that ever since C99, there is a type generic macro that inserts the correct call based on type.

So perhaps I am using the wrong dialect?

Does anyone know what the Compiler Default is in xcode7, and whether it has the generic macro?

The macro is defined in another header?! `Defined in header ` — Ulrich Thomas Gabor, Sep 03 '15 at 12:50
I am not, it looks like the C code incs math.h. Is there anything I need to know before adding this, or is this really super-generic? — Maury Markowitz, Sep 03 '15 at 12:51

score 2 · Accepted Answer · answered Sep 03 '15 at 13:01

2

The generic macro is defined in <tgmath.h>, so you need to #include it, as shown in the following snippet:

#include <tgmath.h>
#include <stdio.h>

int main() {
  long double ld = 3.14;
  double d = 3.14;
  float f = 3.14f;
  printf("%Lf %lf, %f\n",fabs(ld), fabs(d), fabs(f));
  return 0;
}

It compiles flawlessly with

gcc -Wall -Wextra a.c -oa -std=c99

answered Sep 03 '15 at 13:01

serge-sans-paille

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Works great, after a few imports. There's no downside to this, the code in question is purely the generics? – Maury Markowitz Sep 03 '15 at 13:08
Apart from relying on c99, I guess not. – serge-sans-paille Sep 03 '15 at 13:10
And I'm sure this is *purely* coincidental, but as a side effect of #importing these I noticed and changed a few #includes too. And now the app builds about ten times as fast. Sweet! – Maury Markowitz Sep 03 '15 at 13:15

fabs vs. fabsl, should I ever have to type fabsl in my source?

1 Answers1