Question

So I have a really large pointer, p, pointing to roughly 40 bytes.

I also know that these 40 bytes enclose ints, chars, and other pointers. I know how to hop across these 40 bytes too.

For debug purposes I want to print out these contents. How do I do that?

For example, lets say I know that at p+16 there is an int and I want to print this int. Is there a way to “print 4 bytes from this address and format that as an int” in C?

Answer 1

Yes, just cast & dereference. Assuming you have p already set up:

int i = *(int *)(p + 16);
printf("%d\n", i);

Watch out for potential alignment issues – for example, this code:

int i = *(int *)(p + 3);

might cause an exception on some processors (assuming p is safely aligned for an int, that is). In that case, you’ll need to assemble the bytes yourself. Here’s an example assuming a 4-byte integer and 8-bit bytes. Make sure to watch out for endianness:

unsigned char *p;
int bigEndian = p[3] << 24 + p[4] << 16 + p[5] << 8 + p[6];
int littleEndian = p[3] + p[4] << 8 + p[5] << 16 + p[6] << 24;