Question

What does the following way of defining a variable mean? #define COUNT ((long) (sizeof(long) <<1))

Answer 1

it's a macro that defines COUNT as the size of a long shifted one bit to the left

sizeof(long) = 4
0100

moved one bit to the left 1000 or 8

Answer 2

so how do i write macros?

Answer 3

like what defines it, how would i write another one if I wanted to? and why not just use a 8 byte variable type.

Answer 4

And how exactly would I use the macro? esp seince it's called a function.

Answer 5

this one is a variable.
macros can also be functions though
```
//taken from http://stackoverflow.com/a/3437442/2761134
#define MAX(a,b) ((a) > (b) ? a : b)
#define MIN(a,b) ((a) < (b) ? a : b)
```

Answer 6

https://gcc.gnu.org/onlinedocs/cpp/Macros.html

Answer 7

Macros are executed by the preprocessor, and they only ever do text replacement.
```
#define MAX(a,b) ((a) > (b) ? a : b)

int f() {
return MAX(2, 4);
}
```
Putting this through the preprocessor will get you something like:
```
int f() {
return ((2) > (4) ? 2 : 4);
}
```
Which will then later on be compiled. So obviously your macros should only do really simple things. Other languages don't even have this feature, because some consider it dangerous.