C++ meaning of [ ]

Question

That's from an example of boosts asio. What does [this] mean? why the []?

acceptor_.async_accept(socket_,
    [this](boost::system::error_code ec)

It's a [lambda](http://stackoverflow.com/questions/7627098/what-is-a-lambda-expression-in-c11). — Angew is no longer proud of SO, Mar 11 '14 at 13:34
It's part of a [Lambda Expression](http://en.cppreference.com/w/cpp/language/lambda). — Fred Larson, Mar 11 '14 at 13:34

score 6 · Accepted Answer · edited Jun 13 '15 at 21:58

It is a lambda expression used to create a function as an expression

[] is the capture list

A list of symbols can be passed as follows:

[a,&b] where a is captured by value and b is captured by reference.

[this] captures the this pointer by value

[&] captures all automatic variables mentioned in the body of the lambda by reference

[=] captures all automatic variables mentioned in the body of the lambda by value

[] captures nothing

score 4 · Answer 2 · answered Mar 11 '14 at 13:36

4

It is a part of a lambda expression. Look here for more info.

answered Mar 11 '14 at 13:36

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C++ meaning of [ ]

2 Answers2

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