"ARRLEN" Role

[Alcatraz]

Hi everyone,
I'm new to this forum and to C programming,so i'm looking forward for someone who can kindly help me with my currently newbie path...
Can someone explain me how ARRLEN (array length) works?
Is that a prototype or is a builded function that can be used?
I almost studied C from the beginning to his algorythms and i can imagine that ARRLEN is a function that should be used to get back the size of the array, but i'm not really sure and i'm doing crazy to find the answer.
Please help!! I'm sure i'll find kind people that knows the answer and maybe explaing better to me.

[GReaper]

It being all uppercase, I'm going to make an informed guess and say it's a simple macro that simply uses "sizeof" on a string literal or on a static array, like this:

#include <stdio.h>
#define ARRLEN(s) (sizeof(s)/sizeof(*s))

int main(void)
{
    int array[] = { 1, 2, 3, 4, 5 };

    printf("Array length: %u", ARRLEN(array));

    return 0;
}

Maybe it's some built-in macro of your compiler or maybe the code you're currently reviewing has it defined somewhere.

[Alcatraz]

Thank you for help. When you declare ARRLEN why that (s) nearby? ( /*ARRLEN(s)*/ ).
Can we use this even with pointers as you did? ( /* /sizeof(*s) */ ).
And at least,what do you mean by "has it defined somewhere"?
By the way i want to clear out that I'll have soon an C prog exam so i need to clear all my doubts.
If that's a macro,so a symbolic costant, the scary ARRLEN name is a whatsoever name that can even be called "MOMMY" right?
If you or someone else continue explaining you'll give me a big help

[GReaper]

Macros can take arguments, that's what the "(s)" stands for in this context. "s", being the representation of the passed argument, is being substituted with the value you gave it when you use it. For example, in the code I posted:

printf("Array length: %u", ARRLEN(array));
// Becomes
printf("Array length: %u", (sizeof(array)/sizeof(*array)));

Yes, you can use sizeof with anything. You can use it with variables as well as types. To get the correct size for arrays though, it must be a static array in a context the compiler already knows about. For example, if you pass a static array to a function and call sizeof there, the compiler only sees a pointer, it can't know the real size.

By "defined elsewhere" I mean exactly that, it may be defined in a header file, another part of the source file or even in the compiler's global defines.

The macro name is of course whatever its creator wants it to be.

[Alcatraz]

Indeed I thought that when i red about "reserved words" for C and connecting that it's just a sizeof
I've been searching everywhere for this little mind trick. Thank you for clearing my doubts!
Can I write again if I have some problems in this preparation days?

[GReaper]

You are welcome to ask any questions you want, but keep in mind that sometimes it's better to solve something without help.