Question

Could someone explain what this code does

size = *(int *)data;        // size of string plus header word
off = (size + 3) & ~3;
chan = *(int *)(data + off);
data[size] = '\0';      // zero terminate

I think it’s got something to do with making the data a multiple of 4?

Answer 1

Assuming that data is a char*…

size = *(int *)data;        // size of string plus header word

data is interpreted as a pointer-to-int, then dereferenced and assigned to size.

off = (size + 3) & ~3;

This rounds size upwards to the nearest multiple of 4, and assigns to off.

chan = *(int *)(data + off);

The value for chan apparently resides off bytes from data.

data[size] = '\0';      // zero terminate

That one is obvious.