Atmel CAVR-4 Manual De Usuario

CAVR-4

Part 2. Compiler reference

struct str 

{

  char a;

  unsigned long b[];

};

struct str * GetAStr(int size)

{

  return malloc(sizeof(struct str) +

                sizeof(unsigned long) * size);

}

void UseStr(struct str * s)

{

  s->b[10] = 0;

}

The 

struct

 will inherit the alignment requirements from all elements, including the 

alignment of the incomplete array. The array itself will not be included in the size of the 
struct. However, the alignment requirements will ensure that the struct will end exactly 
at the beginning of the array; this is known as padding.

In the example, the alignment of 

struct

 

str

 will be 4 and the size is also 4. (Assuming 

a processor where the alignment of 

unsigned

 

long

 is 4.)

The memory layout of 

struct

 

str

 is described in the following figure.

An array may have an incomplete 

struct

, 

union

, or 

enum

 type as its element type. The 

types must be completed before the array is used (if it is), or by the end of the 
compilation unit (if it is not).

a

First long element of b

Second long element of b

...

pad 

byte

pad 

byte

pad 

byte