C++ .erase()

In C++, the .erase() function removes a single element or a range of elements from a vector. When it removes an element, the size of the vector decreases and the elements after the deleted one are shifted to fill the gap. To remove a range, iterators such as .begin() and .end() are used to specify the start and end positions of the elements to erase.

Syntax

vector.erase(position); // Removing an element
vector.erase(starting_position, ending_position); // Removing multiple elements

Parameters:

• position: An iterator pointing to the position of the element to be removed.
• starting_position: An iterator indicating the beginning of the range of elements to be removed.
• ending_position: An iterator indicating the end of the range of elements to be removed.

Return value:

The .erase() function doesn’t return any value.

Example 1: Removing an Element Using .erase()

In this example, the .erase() function removes a single element from a vector:

#include <iostream>
#include <vector>

int main()
{
  // Declare a vector
  std::vector<int> room;

  // Add values
  for(int i=1; i<=10; i++) room.push_back(i);

  // Remove the 3rd element
  room.erase(room.begin()+2);

  // Print the remaining elements in the vector
  std::cout << "Rooms available:";

  for (unsigned i=0; i<room.size(); ++i)
    std::cout << ' ' << room[i];
  std::cout << '\n';

  return 0;
}

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The output for this code is:

Rooms available: 1 2 4 5 6 7 8 9 10

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Example 2: Removing Multiple Elements Using .erase()

This example uses .erase() to remove a range of elements from a vector:

#include <iostream>
#include <vector>

int main()
{
  // Declare a vector
  std::vector<int> room;

  // Add values
  for(int i=1; i<=10; i++) room.push_back(i);

  // Remove the last 3 elements
  room.erase(room.begin()+7, room.end());

  // Print the remaining elements in the vector
  std::cout << "Rooms available:";

  for (unsigned i=0; i<room.size(); ++i)
    std::cout << ' ' << room[i];
  std::cout << '\n';

  return 0;
}

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The output for this code is:

Rooms available: 1 2 3 4 5 6 7

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Codebyte Example: Using .erase() with a Map

This codebyte example uses .erase() to remove a key-value pair from a map:

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Here, the key-value pair in which the key is “Bob” will be removed.

Frequently Asked Questions

1. Can I use .erase() inside a loop?

Yes, you can use .erase() inside a loop, but with caution. When erasing while iterating, always update the iterator correctly to avoid invalidation issues.

2. What happens if I try to erase a non-existing key from a map using .erase()?

Nothing — no error will occur if you try to erase a non-existing key from a map using .erase(). The size remains unchanged.

3. How efficient is .erase()?

The efficiency of .erase() depends on what it is applied on:

• Vector/String: Linear time O(n) since elements may need to shift.
• Map/Set: Logarithmic time O(log n) due to tree structure.
• Unordered map/Unordered set: Average constant time O(1).