Converting unsigned chars to signed integer

Question

I have an unsigned char array with 2 elements that represents a signed integer. How can I convert these 2 bytes into a signed integer?

Edit: The unsigne

Answer 1

The portable solution:

unsigned char c[2];
long tmp;
int result;

tmp = (long)c[0] << 8 | c[1];
if (tmp < 32768)
    result = tmp;
else
    result = tmp - 65536;

This assumes that the bytes in the array represent a 16 bit, two's complement, big endian signed integer. If they are a little endian integer, just swap c[1] and c[0].

(In the highly unlikely case that it is ones' complement, use 65535 instead of 65536 as the value to subtract. Sign-magnitude is left as an exercise for the reader ;)