Question

typedef struct {
  unsigned char a,
  unsigned char b, 
  unsigned char c
}type_a;

typedef struct {
 unsigned char e,
 unsigned char f[2]
}type_b;

type_a sample;
sample.a = 1;
sample.b = 2;
sample.c = 3;

How do I typecast it and assign new value like:

sample = (type_b)sample; // syntax error
sample.f[1] = 'a';

Answer 1

You can’t cast one data type to another incompatible data type. However, the memory is open for you. You can access it as follows:

typedef struct
{
  unsigned char a;
  unsigned char b; 
  unsigned char c;
}type_a;

typedef struct
{
 unsigned char e;
 unsigned char f[2];
}type_b;

type_a sample;
sample.a = 1;
sample.b = 2;
sample.c = 3;

type_b *sample_b = (type_b *) ((void*) &sample);

Try out yourself accessing sample_b->e and sample_b->f and see what happens.