Possible Duplicate:
Is typedef and #define the same in c?
Confused by #define and typedef
Is there any difference between the following:
#define NUM int
...
NUM x;
x = 5;
printf("X: %d\n", x);
And this:
typedef int NUM;
...
NUM x;
x = 5;
printf("X : %d\n", x);
Both tests compile and run without problems. So, are they equivalent?
Thanks.
There is a difference when you want to create an alias of a pointer type.
typedef int *t1;
#define t2 int *
t1 a, b; /* a is 'int*' and b is 'int*' */
t2 c, d; /* c is 'int*' and d is 'int' */
Moreover, typedef obeys scope rules, i.e. you can declare a type local to a block.
On the other hand, you can use #define when you want to manage your type in a preprocessor directive.
