Simple C++0x question about lambda type

Posted on 2011-09-03
Last Modified: 2012-05-12
This is just a simple question about lambdas in C++0x (well, before it becomes C++11 or C++0xB or something):

While surfing Stroustrup's site, in his C++0x area he gives the following example code which helps describe lambdas.  I get almost all of it except for the third argument in the methods for fill and sort, not on this side but on the method definition side.

Here's his example:  ( Found at )

	void f(vector<Record>& v)
		vector<int> indices(v.size());
		int count = 0;
		fill(indices.begin(),indices.end(),[&count](){ return ++count; });

		// sort indices in the order determined by the name field of the records:
		std::sort(indices.begin(), indices.end(), [&](int a, int b) { return v[a].name<v[b].name; });
		// ...

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My understanding (and please correct me if I'm wrong) of the arguments passed in to fill() and sort() are:  the first argument is a pointer to the first element in the vector indices, the second argument points to the last element in indices, and the third is the function method to be used for stepping through the vector in the call to fill() and for comparison in the call to sort().

So my question is:  What does the signature look like for these particular methods for fill() and sort()?

Other questions:
What does this signature actually look like when defined, how would you write this?  Assuming the third argument of each is a delegate, where would you put the delegate defintion?    The lambdas appear to take different argument counts (all of which happen to be by reference in this case, but I'm speaking specifically to argument count), so it seems unlikely they would be the same delegate, unless there exists a generic signature that takes all counts and forms of parameters that I am unaware of ... unless () does in fact do this?

Question by:coder1313514512456
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Accepted Solution

evilrix earned 250 total points
ID: 36479220
Fill and sort are just standard algorithms that are part of C++.

In both cases the 3rd param is just a tenplated parameter. When passing a lamda it is just used as a template argument.

Unless C++0X has introduced a feature I've not yet read about, delegates are not a construct in ANSI standard (unmanaged) C++.

Author Closing Comment

ID: 36479317
Works for me, thanks!  I realize that the methods are standard, but thanks for the links giving the definitions.  I was thinking of a number of different languages when I wrote that, sorry for the confusion on the templated parameter.  And thanks for the quick response.

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