Question

I’ve got this code, which I don’t understand why it doesn’t compile:

typedef struct 
{
  uint32_t serial_number;
  uint32_t ieee_address[6];
} FACTORY_CONFIG; 

...
// Unlock flash (only the portion we write on)
    error = FLASHD_Unlock ( writeaddress, writeaddress + sizeof ( FACTORY_CONFIG.serial_number ), 0, 0 );

When I run it, I get this error:

Error[Pe018]: expected a “)”

When I change the

FACTORY_CONFIG.serial_number

to

FACTORY_CONFIG

, it compiles and everything works. I’m not sure, can I check the size of a type inside a structure ?

Answer 1

You can’t just access members of types in C like that. You can, however, take sizeof from actual objects. And since sizeof is a compile-time construct, these objects don’t even have to be valid. So the following will work:

sizeof(((FACTORY_CONFIG *)0)->serial_number)

If you use this a lot, or just for readability, you could make a macro out of it.