size

Synopsis

template<
      typename Sequence
    >
struct size
{
    typedef unspecified type;
};

Description

size returns the number of elements in the sequence, that is, the number of elements in the range [begin<Sequence>::type,end<Sequence>::type).

Definition

#include "boost/mpl/size.hpp"

Parameters

Expression semantics

Expression	Expression type	Precondition	Semantics	Postcondition
typedef size<Sequence>::type s;	A model of Integral Constant		Equivalent to typedef distance< begin<Sequence>::type,end<Sequence>::type >::type s;	s::value >= 0

Complexity

The complexity of the size algorithm directly depends on the implementation of the particular sequence it is applied to. In the worst case size has a linear complexity. As a general rule, if the Sequence is a Random Access Sequence, you can be certain that size<Sequence>::type is an amortized constant time operation. The opposite is not necessary true - for example, a model of Forward Sequence still can guarantee you an amortized constant time size complexity. Please refer the documentation page of the concrete sequence type for further information.

Example

typedef list0<> empty_list;
typedef vector_c<int,0,1,2,3,4,5> numbers;
typedef range_c<int,0,100> more_numbers;

BOOST_STATIC_ASSERT(size<list>::type::value == 0);
BOOST_STATIC_ASSERT(size<numbers>::type::value == 5);
BOOST_STATIC_ASSERT(size<more_numbers>::type::value == 100);

See also

Sequence, empty, begin, end