Question

Assuming we have a simple struct like:

typedef struct
{
    int d1;
    int d2;
    float f1;
}Type;

Which is the correct when allocate memory for a new instance of it:

This:

// sizeof *t == sizeof(Type) ( gcc prints 12 bytes)
Type *t = malloc(sizeof *t); 

or:

// sizeof pointer always == 4 (in my case also on gcc)
Type *t = malloc(sizeof(t)); 

Which is the correct?

Answer 1

Type *t = malloc(sizeof *t); 

This is the correct way to allocate the amount of memory needed for a new instance.

Type *t = malloc(sizeof (t)); 

This will only allocate enough storage for a pointer, not an instance.