c++ Beginner Error

[blood08]

Hey I am following a video tutorial teaching pointers... I am following along and writing what they have. Which is:

#include <iostream>

using namespace std;

void main()
{
	int myArray[4] = (1, 2, 3, 4);

	cout << (int)myArray << endl;
	cout << (int)&myArray[1] << endl;
}

They are able to run this.
Now they are using an older version of Visual C++ than I am.

Here is the error I am getting when I try to run it:

1>------ Build started: Project: HelloWorld, Configuration: Debug Win32 ------
1>Compiling...
1>helloworld.cpp
1>c:\users\--------\documents\visual studio 2008\projects\helloworld\helloworld\helloworld.cpp(7) : error C2440: 'initializing' : cannot convert from 'int' to 'int [4]'
1>        There are no conversions to array types, although there are conversions to references or pointers to arrays
1>Build log was saved at "file://c:\Users\--------\Documents\Visual Studio 2008\Projects\HelloWorld\HelloWorld\Debug\BuildLog.htm"
1>HelloWorld - 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

How can this be fixed

[falloutphil]

Hi,

It's hard to say without knowing what they are trying to achieve on the tutorial, firstly you should use curly braces to initalize an array at creation:

int myArray[4] = {1, 2, 3, 4};

Secondly, the compiler is right here - what you are asking the compiler to do is convert an object of type array to an object of type int - there is no sensible way to do that. I'd need to know what the code is trying to achieve to write it for you.

Quick point here - don't use old C-style casts i.e. (int) - instead use:

static_cast<int>(myArray)

This will tell the compiler exactly what it is you are trying to do - and may yield better error messages, and also it will stop you accidentally doing a different type of cast (dynamic_cast or reinterpret_cast - see google).

The compiler doesn't seem to be complaining about the last line - code like this is pretty nasty and should be avoided, but for demonstration of pointers I guess it's OK. What do they say this should do?

Phil.

[blood08]

It should display the memory address of the variable.

[falloutphil]

OK - The code you originally posted actually compiles OK on GCC 4.0.1, so I'm not sure why it's failing on your compiler.

I get it now - they are just demonstrating that myArray is just a pointer to the first int element and &(myArray[1]) is just the address of the second element - note the brackets to make it clear.

Slight correction to what I originally said - you cannot use a static_cast here as you are asking the compiler to reinterpret from - from a pointer to a value. Thus you want to use reinterpret_cast. On GCC using reinterpret_cast compiles correctly and gives exactly the same result as your original code, static_cast produces the same compile time error you are seeing - saying it cannot convert.

A few other points - cout should be able to handle printing out pointers without casting them - thus if you remove the cast altogther you should see the hex memory addresses of the pointer printed out (showing that array[1] is one size_of(int) above array[0] in memory - I'm assuming that is what they are trying to get you to see).

If you want to use a cast try the below code - note I have replaced int with 'unsigned int' - that is because a memory address cannot be negative (an int can) so unsigned int (values >=0 only) represents a better range.

Try this:

#include <iostream>

using namespace std;

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

  cout << reinterpret_cast<unsigned int>(myArray) << endl;
  cout << reinterpret_cast<unsigned int>(&myArray[1]) << endl;

  return 0;
}

[blood08]

Problem Solved...
Thanks, you have been very helpful.

+1Rep