std::list insert

Introduction

std::list is a container in the C++ Standard Template Library (STL) that provides constant time insertion and removal of elements in any position.

The insert() method of std::list is used to insert elements at any position in the list.

Syntax

iterator insert( const_iterator pos, const T& value );
iterator insert( const_iterator pos, T&& value );
iterator insert( const_iterator pos, size_type count, const T& value );
template< class InputIt >
iterator insert( const_iterator pos, InputIt first, InputIt last );
iterator insert( const_iterator pos, initializer_list<T> ilist );

Parameters

• pos : Position where the element(s) will be inserted.
• value : Element to be inserted in the list.
• count : Number of elements to be inserted.
• first and last : Iterators to the beginning and end of a range of elements.
• ilist : Initializer list of elements to be inserted.

Return value

The method returns an iterator to the inserted element.

Examples

Inserting a single element

std::list<int> myList = {1, 2, 3};
auto it = myList.begin(); 
it++; // point to second element (value 2)
myList.insert(it, 4); // insert 4 before the second element (value 2)
// resultant list: {1, 4, 2, 3}

Inserting multiple elements

std::list<int> myList = {1, 2, 3};
auto it = myList.begin(); 
it++; // point to second element (value 2)
myList.insert(it, 3, 4); // insert 3 copies of 4 before the second element (value 2)
// resultant list: {1, 4, 4, 4, 2, 3}

Inserting elements from a range

std::list<int> myList = {1, 2, 3};
std::vector<int> vec = {4, 5, 6};
auto it = myList.begin(); 
it++; // point to second element (value 2)
myList.insert(it, vec.begin(), vec.end()); // insert the elements from vec before the second element (value 2)
// resultant list: {1, 4, 5, 6, 2, 3}

Inserting elements from an initializer list

std::list<int> myList = {1, 2, 3};
auto it = myList.begin(); 
it++; // point to second element (value 2)
myList.insert(it, {4, 5, 6}); // insert the elements from the initializer list before the second element (value 2)
// resultant list: {1, 4, 5, 6, 2, 3}

Conclusion

The insert() method of std::list is a very useful method for inserting elements at any position in the container. It provides flexibility and convenience to the programmer, allowing them to choose from various options and approaches to insert elements in their list.