CODEWITHSUNDEEP
cstructclangtypedefanonymous-struct
Nathan Day
Nathan Day

Reputation: 6047

Is this a clang bug? anonymous structs for typedef

I had this typedef for a struct like

typedef struct { double x, y; } ACVector;

and when I look at instances of this in the debugger I get very strange output something like

(lldb) p _translation
(ACVector) $1 = {
  (double) x = -5503.61
  (double) y = -5503.61
  (CLLocationDegrees) latitude = -5503.61
  (CLLocationDegrees) longitude = -1315.67
}

(lldb) p _translation.x
(double) $2 = -5503.61
(lldb) p _translation.y
(double) $2 = -5503.61

if I change the definition of ACVector to 

typedef struct ACVector { double x, y; } ACVector;

and do the same in the debugger I get what I expect

(lldb) p _translation
(ACVector) $1 = {
  (double) x = -5503.61
  (double) y = -1315.67
}

It is legal to use anonymous structs for typedef

OK so more code

the declaration of _translation is as an instance variable

ACVector    _translation;

I use this function to initialise the variable

ACVector ACVectorMake( double x, double y )
{
    ACVector    r;
    r.x = x;
    r.y = y;
    return r;
}

Like this

_translation = ACVectorMake( d[xp[0]].x-s[xp[0]].x,  d[xp[0]].y-s[xp[0]].y );

Originally it was a

ACVector ACVectorMake( double x, double y )
{
    return (ACVector){x,y};
}

And where would the latitude and longitude elements come from in the debugger output, mind you you could not access them individually

More info in response to ACVector defined somewhere else

I have two defines

#define ACVectorZero        (ACVector){(double)0.0,(double)0.0}
#define ACVectorUnit        (ACVector){(double)1.0,(double)1.0}

which interestingly are followed directly by

#define ACDegreesFromDegreesMinutesSeconds( d, m, s )                       (CLLocationDegrees)(d+m/60.0+s/3600.0)
#define ACLocationFromDegreesMinutesSeconds( yd, ym, ys, xd, xm, xs )       (CLLocationCoordinate2D){ACDegreesFromDegreesMinutesSeconds( xd, xm, xs ), ACDegreesFromDegreesMinutesSeconds( yd, ym, ys )}

which could explain perhaps explain the occurrence of latitude and longitude in ACVector

Did a search for every occurrence of ACVector including in libraries, couldn't find any other occurrences of ACVector being defined

This is all using Xcode 4.5 Gold Master

Upvotes: 1

Views: 456

Answers (2)

Jeegar Patel
Jeegar Patel

Reputation: 27240

According to

C language standard n1256

Under 6.7.4 Function specifiers

12
The one exception allows the value of a restricted pointer to be carried
 out of the block in which it (or, more
precisely, the ordinary identifier used to designate it) is declared when
that block finishes execution.

For example, this permits new_vector to return a vector.

typedef struct { int n; float * restrict v; } vector;
vector new_vector(int n)
{
vector t;
t.n = n;
t.v = malloc(n * sizeof (float));
return t;
}

So yes now we can say

It is legal to use anonymous structs for typedef

So now you are doing something else which case unexpected behaviour for you..

Upvotes: 0

Giovanni Funchal
Giovanni Funchal

Reputation: 9200

My bet is that you probably use struct ACVector _translation instead of ACVector _translation in the declaration of your variable.

Please show us more code.

Upvotes: 0

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