enums - type of enumeration constants inside enumerator list in C -

-

edited

i'm working on multi-platform enumeration parser , found weird behaviour while trying answer question above.

question a)

does c standard determine type of enumeration constants before enumeration declaration completed?

for keil armcc, example:

enum e {     val0 = (signed char)126,     val1,     val2,      size0 = sizeof(val0),      size1 = sizeof(val1),      size2 = sizeof(val2)  };

i size0 = 1, size1 = 1, size2 = 8. (if evaluate size of enum constants outside definition, have size of int).

shouldn't equal sizeof( int )? (remembering int, in case, has size of 4 bytes.)

question b)

for keil c251, have following:

signed int value0 = (signed char)-1; enum{ value1 = (signed char)-1 }; enum{ value2 = -1 }; printf( "is value0 equal value1? ---> %s", value0 == value1 ? "yes!" : "no!" ); printf( "is value0 equal value2? ---> %s", value0 == value2 ? "yes!" : "no!" );

which prints:

is value0 equal value1? ---> no! value0 equal value2? ---> yes!

shouldn't both print yes?

is there difference between definitions of value0 , value1 i'm missing, maybe type cast? or compiler bug?

in c (unlike c++), enumeration constant of type int. it's legal refer enumeration constant before end of type declaration.

if keil armcc giving sizeof(val0) != sizeof (int), val0 enumeration constant, keil armcc not conforming c compiler. i've seen other questions here indicate it's non-conforming.

being non-conforming not compiler bug (unless vendor claims it's conforming, far know don't).

as part b:

enum e{     min_signed_char_0 = (signed char)( -128 ),     min_signed_char_1 = -128,     min_signed_char_2 = (  signed int)(signed char)( -128 ),     min_signed_char_3 = (unsigned int)(signed char)( -128 ),     min_signed_char_0_plus_1 = min_signed_char_0 + 1,     min_signed_char_1_plus_1 = min_signed_char_1 + 1,     min_signed_char_2_plus_1 = min_signed_char_2 + 1,     min_signed_char_3_plus_1 = min_signed_char_3 + 1, };

almost conforming c compiler should give min_signed_char_{0,1,2} constants value -128 (of type int), , min_signed_char_{0,1,2}_plus_1 constants value -127 (also of type int). possible wiggle room implementation schar_min == -127, possible unlikely, , apparently not case keil compiler(s). if you're getting different results, either it's bug in compiler.

but definition of min_signed_char_3 problematical. int value -128 converted signed char, doesn't change value. converted unsigned int yields uint_max+1-128 (assuming 32 bits, 4294967168). enumeration constant specified value outside range of int constraint violation, requiring diagnostic. (did compile-time warning?) result, if compiler doesn't reject program, undefined.


Comments

Post a Comment

Popular posts from this blog

ios - Memory not freeing up after popping viewcontroller using ARC -

-
hi project arc based, using uinavigationcontroller make transition between viewcontroller. using profiler analyse happening behind scene memory. noticed when push viewcontroller allocate memory components , when pop not freeing allocated memory. since using arc unable implement dealloc or release component. have analysed in detail , there no memory leak in project. i not using strong property push viewcontroller. here how pushing viewcontroller. viewcontroller *obj = [[viewcontroller alloc] init]; [self.navigationcontroller pushviewcontroller:obj animated:no]; any clue whats going on? should free memory have consumed. please advise your description indicates have retain cycle, leads objects not being deallocated. typical source of retain cycles properties assigned loading nib files (usually declared iboutlet ). two strategies break them , release objects: declare property weak : @property (nonatomic, weak) iboutlet uilabel *statuslabel; set property nil in...
Read more

Django REST Framework perform_create: You cannot call `.save()` after accessing `serializer.data` -

-
i have following viewset: class artistprofileviewset(viewsets.modelviewset): queryset = artistprofile.objects.all() serializer_class = artistprofileserializer def perform_create(self, serializer): if serializer.is_valid(): serializer.save() with following serializers: class simpleartisttrackserializer(serializers.hyperlinkedmodelserializer): class meta: model = artisttrack fields = (...my fields...) class artistprofileserializer(serializers.hyperlinkedmodelserializer): owners = userserializer(many=true, required=false) tracks = simpleartisttrackserializer(many=true, required=false) class meta: model = artistprofile fields = (...my fields...) i getting following error: assertionerror: cannot call `.save()` after accessing `serializer.data`.if need access data before committing database inspect 'serializer.validated_data' instead. i don't see editing serializer.data object. th...
Read more

Why does Go error when trying to marshal this JSON? -

-
i'm trying rather simple example of trying decode json file structs using golang. however, when attempting error that json: cannot unmarshal object go value of type []main.track which don't understand. here's code in question, , json can found here . package main import ( "encoding/json" "fmt" "net/http" "os" ) // tracks group of track types type tracks struct { tracks []track } // track represents singular track type track struct { name string url string artist artist } // artist represents single artist type artist struct { name string mbid string url string } func main() { url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=netherlands" response, err := http.get(url) if err != nil { fmt.printf("%s\n", err) os.exit(1) } de...
Read more