Re: Compilation Error

"Alf P. Steinbach" <>
Sun, 08 Feb 2009 13:38:02 +0100
* Sunil Varma:

int arr[10] = {0};


#include <iostream>
using namespace std;

extern int arr[];


void main()

The result type of 'main' must be 'int', both in C and C++.

No other result type is allowed.

If your compiler accepts 'void' then the compiler is non-conforming (one would
guess that you're using Microsoft's Visual C++).


When I try to build the above code, I'm getting the following
compilation error.

f:\programs\nest\nest\main.cpp(23) : error C2070: 'int []': illegal
sizeof operand

Yes, the size is not known locally in 'main'.

I would like to know the reason why I get a compilation error.
When I change the extern to

extern int *arr;

the code compiles properly.

But only gives you the size of a pointer, not of the array.

For what you appear to want a reasonable solution is to use 'std::vector', and
to avoid running into the static initialization order fiasco (see the FAQ)
provide it via e.g. a Meyers' singleton, like

   <code file="other.cpp">
   #include <vector>

   std::vector<int>& arr()
       static std::vector<int> theArray( 10 );
       return theArray;

   <code file="main.cpp">
   #include <vector>
   #include <iostream>

   std::vector<int>& arr();

   int main()
       using namespace std;
       cout << arr().size() << endl;

*However*, global variables, which this essentially is, are generally Very
Evil(TM) and should be avoided.

It's also a good idea to provide a header for a separately compiled file or set
of files like that.

What book are you using that doesn't explain use of 'std::vector' and doesn't
explain use of headers and doesn't explain the evilness of global variables?

Cheers & hth.,

- Alf

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