但在某些极少数情况下，你需要从首页去刚 INT ，说。在和这些罕见的情况下，只是做了的static_cast 闭嘴编译器，让你的意图明确。甚至是自定义的的static_cast 般 narrowTo 运行，为前pressiveness ...

干杯和放大器;心连心，

I need a common rule for warnings in x64 mode. Which way is better?

Consider the following lines of some code

const int N = std::max_element(cont.begin(), cont.end()) - cont.begin();

or

const int ARR_SIZE = 1024;
char arr[ARR_SIZE];
//...
const int N = std::max_element(arr, arr + ARR_SIZE) - arr;

It is my usual code. I have no problems with x86.

But if I run compiler in x64 mode I have some warnings:

conversion from 'std::_Array_iterator<_Ty,_Size>::difference_type' to 'int', possible loss of data
conversion from '__int64' to 'int', possible loss of data

I want to solve these problems by common rule. Which way is better?

Making static_cast:

const int N = static_cast<int>(
     std::max_element(cont.begin(), cont.end()) - cont.begin()  );

I think this is not general-purpose. And too much letters.

Replace output type with ptrdiff_t:

const ptrdiff_t N = std::max_element(cont.begin(), cont.end()) - cont.begin();

What should I do then with this unknown type ptrdiff_t? I'll get another dozen warnings then. I want to make many operations with N: save, addition, multiplication, cycles and etc. Important: but what if std::_Array_iterator<_Ty,_Size>::difference_type and ptrdiff_t are different types?

Replace output type with std::_Array_iterator<_Ty,_Size>::difference_type:

//h-file
struct S {
    type mymember; // What is the type?
};


//cpp-file
typedef std::vector<int> cont_t;
const cont_t::difference_type N = std::max_element(cont.begin(), cont.end()) - cont.begin();
// Save N
S mystruct;
mystruct.mymember = N; // What type of mystruct.mymember?

How should I save N? What type of mystruct.mymember? I don't know it in h-file.

Your solution.

"what if std::_Array_iterator<_Ty,_Size>::difference_type and ptrdiff_t are different types?" Don't use such a compiler. Also, chances are that it can't formally be different. E.g. this is the case for a vector using the default standard allocator, since that's where it fetches its typedefs, but since the formal guarantee doesn't matter (he he, it really doesn't) I'm not going to look this up in the C++0x draft.

So, use ptrdiff_t.

But it can be a good idea to add a few typedefs, like

typedef ptrdiff_t Size;
typedef ptrdiff_t Index;

and then in your concrete case you'd use Index.

These typedefs are naturally accompanied by custom freestanding countOf, startOf and endOf functions, enabling you to treat raw arrays and standard library containers in exactly the same way.

When you see the name Index it's a bit more clear that it's an index, which can't very naturally get out of the Index or Size set of types almost no matter what you do. E.g., add something to it, it's still an Index. So mostly there will not be a "another dozen warnings".

But in some rare case you'll need to get from Index to just int, say. In and in those rare cases just do a static_cast to shut up the compiler and make your intent clear. Or even a custom static_cast-like narrowTo operation, for expressiveness...

Cheers & hth.,