https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61584
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Structures-unions-enumerations-and-bit-fields-implementation.html The integer type compatible with each enumerated type (C90 6.5.2.2, C99 and C11 6.7.2.2). Normally, the type is unsigned int if there are no negative values in the enumeration, otherwise int. If -fshort-enums is specified, then if there are negative values it is the first of signed char, short and int that can represent all the values, otherwise it is the first of unsigned char, unsigned short and unsigned int that can represent all the values. On some targets, -fshort-enums is the default; this is determined by the ABI. --- CUT --- C++ semi-follows C here, though instead of being a compatible type, it is the underlying type.