Re: Question about INT_PTR and int

"Giovanni Dicanio" <>
Mon, 3 Nov 2008 11:37:40 +0100
"Mikel" <> ha scritto nel messaggio

for (INT_PTR i = 0; i < myArray.GetCount(); i++)
   c_List.InsertItem(i, [...]);

The problem is I get a warning C4244 in InsertItem, because InsertItem
takes an int, so I'm converting an INT_PTR to int.

I would write the loop using 'int', because CListCtrl::InsertItem() requires
a an int for the item index.

In fact, you wrote a correct thing here:

Actually, I'm quite sure myArray won't be as big as to really have a
problem with this, and if it were, a CListCtrl would not be a good way
to show its contents.

So, just do:

 int count = static_cast< int >( myArray.GetCount() );
 for ( int i = 0; i < count; i++ )
     c_List.InsertItem(i, ... );

A similar problem occurs with STL containers, that tend to use a size_t to
represent size, and size_t is defined as 'unsigned int', so in case you use
e.g. std::vector instead of CArray in the loop, there is a type mismatch in
the loop index (int) and array size (size_t).
As you kind of already wrote, considering that an int can store a maximum
positive value of 2^31-1 (on 32 bit) = 2,147,483,647, I consider that value
in lots of cases as a good reasonable maximum value.

However, for very robust code, you may consider a debug assertion (or
throwing a C++ STL exception) before the cast (at least for a size_t based

 ASSERT( myVector.size() <= 2147483647 );
 int count = static_cast< int >( myVector.size() );
 for ( int i = 0; i < count; i++ )
    c_List.InsertItem( i, ... );

Or you may define a safe conversion function:


inline int size2int( size_t s )
    // Make sure the cast from size_t to int is safe
    const int maxValue = 2^31 - 1;
    ASSERT( s <= maxValue ); // or throw...

    return static_cast< int >( s );


and just use that.


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