#elements in array in functions

[sql_lall]

Firstly, i know that in normal "int main(void)" stuff, to find the # of elements in an array, say int p[], you do:
num_elem=sizeof(p)/sizeof(int)
(**i think sizeof(p)/sizeof(p[0]) is more general**)

However, i was passing an array to a function:

int my_func(int q[])
{
cout<<sizeof(q)<<endl; //Gives 4 (=sizeof(int)) every time
}

I was just wondering if there was a nice way to find the size of an array passed to a function??

Thanks

[McCain]

Why not just pass the number of elements in the array to the function, that way you don't have to do callculations on unused places in the array. For example

int array[30];

for (int i = 0; i < 10; ++i)
{
	array[i] = i + 1;
}

Now if you do sizeof(array)/sizeof(array[0]) you would get 30, but we've only actually only used 10 spots... If we pass the number of elements to the funcion this is not going to be a problem...

[Zaei]

Pass the number of elements in the array. Doing what you are trying to do is a bad idea, and will only occasionally and under specific circumstances, work.

Z.

[McCain]

Originally posted by Zaei
Pass the number of elements in the array. Doing what you are trying to do is a bad idea, and will only occasionally and under specific circumstances, work.

Z.

Yeah, that's pretty much what I was trying to say

[sql_lall]

Yeah, i get what ur saying, and it would normally work. However, i forgot to add that this is for a competition, and all they do is call your function (actually part of a class) with the parameters as an array.
I.e. you write an class, with a function called "X(int p[])" or whatever. To mark you, they pass and array to X, and test the returned value. Hence, as they do not pass the #elements when testing, the suggestions don't work for this case.
Thanks anyway, all suggestions appreciated

[CornedBee]

What are they passing in the array? There is no way to find out the number of elements in C, it's always your responsibility to keep track of that.

For that matter, what's the wording of the competition problem? Maybe there's a clue.

[sql_lall]

Nah, there's no way to pass the size, all you can do is write a function that accepts an array, thats it.
BTW, i'm using C++, and hoping there is *some* way to do it...

[CornedBee]

Would you fulfill the specification if you wrote an array class that stores the size along with the array?

[parksie]

Like a vector or a Boost.Array?

[CornedBee]

More like boost::array.
Though isn't boost::array constant size through templates?
I was thinking more along the lines of constant size through constructor parameter.

[parksie]

I was doing it their style as Boost.Package not boost:ackage

A vector can be "constant size" through a parameter, and for all intents and purposes is identical speed to a raw array.

[CornedBee]

It wasn't like "more like boost::array than Boost.Array" but rather like "more like boost::array than std::vector".

[parksie]

Oh.

/me beats head on desk

I see what you're getting at now