DevTut

# std::forward_list

std::forward_list is a container that supports fast insertion and removal of elements from anywhere in the container. Fast random access is not supported. It is implemented as a singly-linked list and essentially does not have any overhead compared to its implementation in C. Compared to std::list this container provides more space efficient storage when bidirectional iteration is not needed.

# Example

#include <forward_list>
#include <string>
#include <iostream>

template<typename T>
std::ostream& operator<<(std::ostream& s, const std::forward_list<T>& v) {
    s.put('[');
    char comma[3] = {'\0', ' ', '\0'};
    for (const auto& e : v) {
        s << comma << e;
        comma[0] = ',';
    }
    return s << ']';
}

int main() 
{
    // c++11 initializer list syntax:
    std::forward_list<std::string> words1 {"the", "frogurt", "is", "also", "cursed"};
    std::cout << "words1: " << words1 << '\n';
 
    // words2 == words1
    std::forward_list<std::string> words2(words1.begin(), words1.end());
    std::cout << "words2: " << words2 << '\n';
 
    // words3 == words1
    std::forward_list<std::string> words3(words1);
    std::cout << "words3: " << words3 << '\n';
 
    // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"}
    std::forward_list<std::string> words4(5, "Mo");
    std::cout << "words4: " << words4 << '\n';
}

Output:

words1: [the, frogurt, is, also, cursed]
words2: [the, frogurt, is, also, cursed]
words3: [the, frogurt, is, also, cursed]
words4: [Mo, Mo, Mo, Mo, Mo]

# Methods

Method name Definition
operator= assigns values to the container
assign assigns values to the container
get_allocator returns the associated allocator
--- ---
Element access
front access the first element
--- ---
Iterators
before_begin returns an iterator to the element before beginning
cbefore_begin returns a constant iterator to the element before beginning
begin returns an iterator to the beginning
cbegin returns a const iterator to the beginning
end returns an iterator to the end
cend returns a iterator to the end
Capacity
empty checks whether the container is empty
max_size returns the maximum possible number of elements
Modifiers
clear clears the contents
insert_after inserts elements after an element
emplace_after constructs elements in-place after an element
erase_after erases an element after an element
push_front inserts an element to the beginning
emplace_front constructs an element in-place at the beginning
pop_front removes the first element
resize changes the number of elements stored
swap swaps the contents
Operations
merge merges two sorted lists
splice_after moves elements from another forward_list
remove removes elements satisfying specific criteria
remove_if removes elements satisfying specific criteria
reverse reverses the order of the elements
unique removes consecutive duplicate elements
sort sorts the elements

# Remarks

Adding, removing and moving the elements within the list, or across several lists, does not invalidate the iterators currently referring to other elements in the list. However, an iterator or reference referring to an element is invalidated when the corresponding element is removed (via erase_after) from the list. std::forward_list meets the requirements of Container (except for the size member function and that operator=='s complexity is always linear), AllocatorAwareContainer and SequenceContainer.

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