How to align a class member variable?

There is no way to align a class member variable.  BTW, the same thing is true of members of a C struct.  C++ class members and C struct members are really the same under the covers.  Why do you need such an alignment?  What overarching problem are you trying to solve?

Thanks and regards,

-George

Hi George,

I am trying to optimize a routine which accepts a pointer to an array of floats (which happens to be a class member variable).  I want to take advantage of double word operations using intrinsics, but must guarantee double word alignment for the input float data.

I guess I could use a 64bit dummy variable.  I understand that "__attribute__ ((aligned (8)))" is not supported, is this true?

Thanks.

The traditional way to increase the alignment of a variable is to place it in a union with something that is naturally more strictly aligned. This is not as direct as an alignment pragma or attribute, but it is a bit more portable.

struct S {
   union U {
      double unused;
      float data[N];
   };
};

Archaeologist is correct, of course.  In C++ such anonymous unions are part of the language.  In C, you have to enable the GCC extensions with the --gcc switch.  To make the example a bit more complete ...

class tc {
public:
   union {                 // anonymous union
     float user;
     double never_used;
   };
   int other_field;
};

class tc t;

void f()
{
    t.user = 0.0;           // access is the same
    t.other_field = 5;      // as any other member
}