Where can I look up the definition of size_type for vectors in the C++ STL?

Question

It seems safe to cast the result of my vector\'s size() function to an unsigned int. How can I tell for sure, though? My documentation isn\'t cle

Answer 1

Do not assume the type of the container size (or anything else typed inside).

Today?

The best solution for now is to use:

std::vector::size_type

Where T is your type. For example:

std::vector::size_type i ;
std::vector::size_type j ;
std::vector >::size_type k ;

(Using a typedef could help make this better to read)

The same goes for iterators, and all other types "inside" STL containers.

After C++0x?

When the compiler will be able to find the type of the variable, you'll be able to use the auto keyword. For example:

void doSomething(const std::vector & p_aData)
{
    std::vector::size_type i = p_aData.size() ; // Old/Current way

    auto j = p_aData.size() ;    // New C++0x way, definition
    decltype(p_aData.size()) k;  // New C++0x way, declaration
}

Edit: Question from JF

What if he needs to pass the size of the container to some existing code that uses, say, an unsigned int? – JF

This is a problem common to the use of the STL: You cannot do it without some work.

The first solution is to design the code to always use the STL type. For example:

typedef std::vector::size_type VIntSize ;

VIntSize getIndexOfSomeItem(const std::vector p_aInt)
{
   return /* the found value, or some kind of std::npos */
}

The second is to make the conversion yourself, using either a static_cast, using a function that will assert if the value goes out of bounds of the destination type (sometimes, I see code using "char" because, "you know, the index will never go beyond 256" [I quote from memory]).

I believe this could be a full question in itself.