Solved

# Determining array length

Posted on 2004-08-11
12,415 Views
Actually, this question has two parts.

1. Can C++ arrays only hold primitive types such as int, float, etc? Can it hold abstract types such as:

class A {
...
};

int main() {
A a1, a2, a3;
A a[] = {a1, a2, a3};
myFunc(a); // see part 2
return 0;
}

2. Now for my real question. When passed an array as a parameter, how do I determine the length of the array? This array contains abstract types.

From the example above, suppose I have the following function

void myFunc(A *x) {
// how do I find the length of the array
}

In C, I know that you can do the following

int size = sizeof(x) / sizeof(x[0]);

Thanks a lot everyone.

P.S. I am interested only in arrays. Not vectors.
0
Question by:licz

LVL 11

Expert Comment

1. If you are interested in arrays only.
One way would be to make it an array of pointers and hold the pointers to your abstract classes in the array
0

LVL 23

Accepted Solution

Mysidia earned 405 total points
1. The answer is yes and no.

you can't do  "AbsType name[10];"
since you cannot define a variable of type with pure virtual methods

You can do      AbsType *name = new ConcreteType[10];

2.  You cannot find the size of an array passed as a parameter.
You cannot even do that in C; the code you gave only works for
a static array (Yes, that code works for the same situation in C++ that
it works for in C).

f(int x[]) {
return sizeof(x) / sizeof(x[0]);
}

Will always return  sizeof(int *) / sizeof(int)
which is not the size of the array passed.

In both C and C++

if you want to know the length, then you need to pass it, i.e.

f(int x[],  int numberElementsInArray)
{
...
}

0

LVL 30

Expert Comment

If you're only going to be using static arrays, and the size is variable depending where it's being called, then you can determind the size of the array if you use a template function.

Example:
template<class T>
void MyFunc(T&Src)
{
int Size = sizeof(Src)/sizeof(Src[0]);
cout << Size << endl;
}

int main(int argc, char* argv[])
{
int data1[5] = {1, 2, 3, 4, 5};
MyFunc(data1);

int data2[10] = {1, 2, 3, 4, 5, 1, 2, 3, 4, 5};
MyFunc(data2);

0

## Featured Post

Unlike C#, C++ doesn't have native support for sealing classes (so they cannot be sub-classed). At the cost of a virtual base class pointer it is possible to implement a pseudo sealing mechanism The trick is to virtually inherit from a base class…
Templates For Beginners Or How To Encourage The Compiler To Work For You Introduction This tutorial is targeted at the reader who is, perhaps, familiar with the basics of C++ but would prefer a little slower introduction to the more ad…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.

#### Need Help in Real-Time?

Connect with top rated Experts

16 Experts available now in Live!