C++ vector size types

Question

I just started learning C++ and have a question about vectors. The book I\'m reading states that if I want to extract the size of a vector of type double (for example), I should

Answer 1

The book you’re reading states that if you want to extract the size of a vector of type double (for example), you should do something like:

    vector::size_type vector_size;
    vector_size = myVector.size();

Whereas in Java you might do

    int vector_size;
    vector_size = myVector.size();

Both are inferior options in C++. The first is extremely verbose and unsafe (mostly due to implicit promotions). The second is verbose and extremely unsafe (due to number range).

In C++, do

    ptrdiff_t const vectorSize = myVector.size();

Note that

• ptrdiff_t, from the stddef.h header, is a signed type that is guaranteed large enough.

• Initialization is done in the declaration (this is better C++ style).

• The same naming convention has been applied to both variables.

In summary, doing the right thing is shorter and safer.

Cheers & hth.,