Padding and alignment in CodeWarrior for MC1321x (HCS08)

[drdr]

When creating an array of a bit field structure as in the example below, is it possible to fit two 4-bit array members into a single byte?

typedef struct {
  unsigned int my_location : 2;

  unsigned int my_WATCHDOG : 2;

} foo;

foo my_array[1000] = 0;

Is it possible to have the above result in 500 bytes of 1000 elements, each addressed by my_array[i] or will CW pad every element such that 1000 bytes will be used by the array?

Thanks for the help,

drdr

[CompilerGuru · Accepted solution]

No, not with a simple foo structure.

C requires that array elements have their own addresses, therefore in order to have such a array you will have to pack a single byte in C code.

typedef struct {
  unsigned char my_low_location : 2;

  unsigned char my_low_WATCHDOG : 2;

  unsigned char my_high_location : 2;

  unsigned char my_high_WATCHDOG : 2;

} foo;

foo my_array[500];

Alternatively, and you can also use an array of bytes and then work with macros to implement the accesses to have a direct indexed access.

Daniel

[drdr]

Hi Daniel,

Thanks for the tip.

drdr