/* This checks if enums needing 8 bit but only having positive values are correctly zero extended (instead of sign extended) when stored into/loaded from a 8 bit bit-field of enum type (which itself is implementation defined, so isn't necessarily supported by all other compilers). */ enum tree_code { SOME_CODE = 148, /* has bit 7 set, and hence all further enum values as well */ LAST_AND_UNUSED_TREE_CODE }; typedef union tree_node *tree; struct tree_common { union tree_node *chain; union tree_node *type; enum tree_code code : 8; unsigned side_effects_flag : 1; }; union tree_node { struct tree_common common; }; enum c_tree_code { C_DUMMY_TREE_CODE = LAST_AND_UNUSED_TREE_CODE, STMT_EXPR, LAST_C_TREE_CODE }; enum cplus_tree_code { CP_DUMMY_TREE_CODE = LAST_C_TREE_CODE, AMBIG_CONV, LAST_CPLUS_TREE_CODE }; extern int printf(const char *, ...); int blah(){return 0;} int convert_like_real (tree convs) { switch (((enum tree_code) (convs)->common.code)) { case AMBIG_CONV: /* This has bit 7 set, which must not be the sign bit in tree_common.code, i.e. the bitfield must be somehow marked unsigned. */ return blah(); default: break; }; printf("unsigned enum bit-fields broken\n"); } int main() { union tree_node convs; convs.common.code = AMBIG_CONV; convert_like_real (&convs); return 0; }