Re: [Boost-users] Boost-users Digest, Vol 2769, Issue 5

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Date: Thu, 30 Jun 2011 15:00:13 -0400 (EDT) From: Jeremiah Willcock To: boost-users@lists.boost.org Subject: Re: [Boost-users] [Graph]questions regarding boost::graph::adjacency_list constructor prototype

On Thu, 30 Jun 2011, Tan, Tom (Shanghai) wrote:

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While studying boost.graph, I stumbled upon this constructor

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????template <class EdgeIterator>

??? adjacency_list(EdgeIterator first, EdgeIterator last,

????????????????????????? vertices_size_type n,

????????????????????????? edges_size_type = 0,

????????????????????????? const GraphProperty& p = GraphProperty())

????? : Base(n, first, last), m_property(new graph_property_type(p))

{ }

I have 2 questions here:

-????????? What does ?edges_size_type = 0,? means here?? Assigning a

value to a TYPE, instead of a parameter? Can

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anyone please point me to an explanation of this grammar usage?

It's like if the code was "edges_size_type x = 0", but since the

definition: parameter

is not used, removing the name avoids compiler warnings.

Nice to know this trick. Never knew that the 'x' can be omitted in this case.

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-????????? Why the necessary of edges_size_type = 0 parameter,?

since there?s a range pair of ?EdgeIterator first,

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EdgeIterator last??

It is not necessary, since the value of that parameter is never used. It is probably there match the interface of some other constructor, either in adjacency_list or some other graph class.

I guessed so but it's better to confirmed. Thanks for the help. -Tom