CODEWITHSUNDEEP
cpointers
kumar
kumar

Reputation: 2580

pointer is always byte aligned

I read something like pointer must be byte-aligned. My understanding in a typical 32bit architecture... all pointers are byte aligned...No ?

Please confirm.

can there be a pointer which is not byte-aligned ?

Basically this is mentioned in a hardware reference manual for tx descriptor memory.

Upvotes: 2

Views: 446

Answers (3)

Pete Kirkham
Pete Kirkham

Reputation: 49311

In C, a pointer points to an object†

The only objects which are not a whole number of bytes are bit fields.

The C language does not allow you to create a pointer to a bit field; this code will result in a compiler error: "cannot take address of bit-field ‘b’":

struct S { unsigned int a:4, b:4, c:4, d:3, e:1; };

int main ( void ) {
    struct S s;
    int *i = &s.b; // would point half a byte into s
    return 0;
}

Pointers can only be incremented by a whole number of the size of object they point to.

Since you can't create such a pointer to an object of size less than one byte, or increment a pointer by less than one byte, you cannot have a pointer which is less than one byte aligned.

† in the C sense, not the OO sense

Upvotes: 5

Sjoerd
Sjoerd

Reputation: 75598

If a pointer or a number is not byte aligned, it would start in the middle of a byte. I.e. some bits of a byte would belong to one pointer, and other bits to another. This would be strange and it does not occur in practice.

Upvotes: 1

fmark
fmark

Reputation: 58557

Yes, you cannot address any amount of memory smaller than a byte.

Upvotes: 9

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