Macros in
C can be
dangerous if used
sloppily.
If I remove the () from the excellent example above,
we can prove that 2*2 = 3 !
#define inc_macro(x) x+1
main()
{
printf("%d\n",inc_macro(1)*inc_macro(1));
}
% gcc macrotest.c
% a.out
3
The reason for this is that it expands to:
printf("%d"\n",x+1*x+1);
which due to order of operations is the same as x+(1*x)+1 or 1+(1*1)+1.
This is why it is a good idea to include () around your
expression in a #define.
An alternative in C that does not have this problem
is the inline function.