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Asked: 2026-05-25T19:34:10+00:00

#define PORTC *(unsigned char volatile *)(0x1003) #define DDRC *(unsigned char volatile *)(0x1007) So I’ve

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#define PORTC *(unsigned char volatile *)(0x1003)

#define DDRC *(unsigned char volatile *)(0x1007)

So I’ve been trying to read some stuff about embedded C. Initially I thought this macro was a pointer-to-pointer type but then I soon assumed the last star is actually a dereference rather than a type-cast, am I correct? Dereferencing to the location 0x1003/0x1007.

It is used like: PORTC = <some hex value>

Question is what makes this different from a pointer type-cast? Is there some sort of ‘provision’ in the C specifications? Or am I just an idiot…

Also I don’t quite know how to phrase this and so I couldn’t do a quick search first…

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1 Answer

  1. Editorial Team

    It’s just the way the C grammar is defined.

    To be a cast, the expression needs parenthesis: (type)sub-expression casts sub-expression to type type.

    Your example, *(unsigned char volatile *)(0x1003) is composed of 2 sub-expressions:

    • a “lonely” star: *
    • a cast: (unsigned char volatile *)(0x1003)

    The cast is composed of the type inside () and a value.

    So, the whole expression is interpreted as a pointer, then de-referenced to set the memory area pointed to.

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