Solved

Determining array length

Posted on 2004-08-11
3
12,430 Views
Last Modified: 2011-08-18
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
Comment
Question by:licz
3 Comments
 
LVL 11

Expert Comment

by:avizit
ID: 11780607
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

by:
Mysidia earned 405 total points
ID: 11780633
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

by:Axter
ID: 11794113
In your example, you're passing a static array to your function.

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

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Often, when implementing a feature, you won't know how certain events should be handled at the point where they occur and you'd rather defer to the user of your function or class. For example, a XML parser will extract a tag from the source code, wh…
Introduction This article is the first in a series of articles about the C/C++ Visual Studio Express debugger.  It provides a quick start guide in using the debugger. Part 2 focuses on additional topics in breakpoints.  Lastly, Part 3 focuses on th…
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

820 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question