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When the result is stored in a variable with a storage capable of holding both values, this is very unexpected. Consider this example: int rc =3D -1; unsigned int foo =3D 123; long x =3D y ? foo : rc; If one of the branch of the ?: is unsigned, then the compiler will cast both branch to unsigned _before_ storing it in x. Despite long being able to store INT_MIN, INT_MAX, UINT_MAX (assuming 64b long/32b int). So if y is 0, it's basically doing long x =3D (long)((unsigned int)-1); Which will result in storing 0x00000000ffffffff (4294967295) instead of expected 0xffffffffffffffff (-1). I thought we hit some sort of weird compiler bug but after reducing the problem to the simple example above and trying it GCC, clang, ICC and MSVC they all do the same thing: https://godbolt.org/z/P5Ts7o1df So it is most likely a C quirk. Standard reads 6.5.15. 5) > If both the second and third operands have arithmetic type, the result > type that would be determined by the usual arithmetic conversions, were > they applied to those two operands, is the type of the result. Cheers, --=20 Aur=C3=A9lien Aptel / SUSE Labs Samba Team GPG: 1839 CB5F 9F5B FB9B AA97 8C99 03C8 A49B 521B D5D3 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 N=C3=BCrnberg, D= E GF: Felix Imend=C3=B6rffer, Mary Higgins, Sri Rasiah HRB 247165 (AG M=C3=BC= nchen)