Mixed indexing behaviour for typedef array?

Question

I have a typedef:

typedef unsigned char MyType[2];

I pass it to a function and the result is FAIL!

void f(MyType * m)
{
*m[0] = 0x55;
*m[1] = 0x66;
}

void main(void)
{
Mytype a;
a[0] = 0x45;
a[1] = 0x89;

f(&a);
}

The manipulation of variable a in main() works on 1 byte indexing, so a is equal to {0x45, 0x89}. However in function f the indexing acts on 2 bytes (the sizeof the type).

So in function f, *m[1] in this instance is actually modifying memory out of bounds.

Why is this, what have I forgotten?

Thanks.

Answer 1

Try:

(*m)[1]

instead of *m[1]

Answer 2

Ah just worked it out after giving up! Brackets Boy, Brackets.

void f(MyType * m)
{
(*m)[0] = 0x55;
(*m)[1] = 0x66;
}

void main(void)
{
Mytype a;
a[0] = 0x45;
a[1] = 0x89;

f(&a);
}