The University of Iowa
The College of Liberal Arts and Sciences
Department of Computer Science
Programming Languages and Tools:
CS:3210:0001
Lecture/Lab #27
Programming with C++
Generic algorithms (cont.), inserter/stream iterators, lambda expressions
Generic algorithms (recap)
- Operate on iterators/iterator ranges, are independent of any particular container type.
- Do impose certain requirements on the element type (e.g. presence of operator ==)
- 100+ algorithms following a consistent architecture / set of patterns:
- operate over a range of elements, typically the first two parameters are iterators that denote the input range
- can modify elements in the containers, do not modify the container itself
- special iterators exist that allow for other side-effects, including modification of containers
Special iterators (<iterator> header)
std::back_inserter( c )
Returns a "back inserter" iterator for c, which appends to the end of c when the iterator is dereferenced and consequently assigned to.
std::front_inserter( c )
Returns a "front inserter" iterator for c, which appends to the beginning of c when the iterator is dereferenced and consequently assigned to.
std::inserter( c, pos )
Returns an "inserter" iterator for c, which inserts elements into c at the position pos when the iterator is dereferenced and consequently assigned to.
std::ostream_iterator<T>(stream, " ")
Returns an output iterator that writes objects of type T into stream using operator<<.
std::istream_iterator<T>(stream)
Returns an input iterator that reads objects of type T from stream using operator>>.
Algorithms with predicates
auto i = find_if( first, last, p );
Returns an iterator to the first element for which predicate p returns true.
auto n = count_if( first, last, p );
Returns the number of elements for which predicate p returns true.
auto i = copy_if( first, last, dest, p );
Copies elements in the range for which predicate p returns true to another range beginning at dest.
replace_if( first, last, p, newv );
Replaces all elements for which predicate p returns true with newv.
auto i = remove_if( first, last, p );
Removes all elements for which predicate p returns true, returns a past-the-end iterator for the new range of values.
auto b = all_of( first, last, p );
Returns true if predicate p returns true for all elements in the range
auto b = any_of( first, last, p );
Returns true if predicate p returns true for at least one element in the range
auto b = none_of( first, last, p );
Returns true if predicate p returns true for no elements in the range
Lambda expressions
A convenient way to define an anonymous function object at the point of use
std::vector<int> v = { 11, 22, 33, 44, 55, 66, 77 };
auto iter = std::find_if( v.begin(), v.end(), []( int n ) {
return n > 42;
} );
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The [] syntax actually serves a purpose and is called a capture clause.
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The empty brackets indicate that the expression body of doesn't accesses variables from the enclosing scope.
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Use [=] to enable capturing all outside variables by value, [&] to capture by reference.
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Beware of lifetime issues if/when passing/returning lambda from a function.
Programming with C++, Spring 2020, Lecture #27
By Aleksey Gurtovoy
Programming with C++, Spring 2020, Lecture #27
Generic algorithms (cont.), inserter/stream iterators, lambda expressions
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