<stdbool.h>
Unless you need compatibility with C89 for some reason, I would use bool for the return type of the function and true and false as the possible values.
It helps readability.
sscanf()
This one depends on your performance needs. A solution using sscanf() will be much easier to understand with a simple look and also shorter in code, but may also be much slower (a benchmark would be appropriate).
<stdint.h>
Same as with bool: segs seems at first glance to be some string, but after some time I realized it's just an array of 8-bit unsigned integers. You should use uint8_t for that.
Unneeded cast
unsigned char *p;
int i;
...
*p = (unsigned char)i;
This cast is not needed.
Usually casts are very dangerous: they can hide bugs that otherwise the compiler would catch easily. Don't ever cast, unless you know a very good reason to.