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C++ Algorithm remove_if()

C++ Algorithm remove_if() function is used to eliminate all the elements that satisfy a predicate from a given range [first, last) without disturbing the order of the remaining elements.

  • This function cannot alter the size of the container.
  • It returns an iterator to the new end of the range.
  • Remove is stable, means that the relative order of the elements that are not removed is remain unchanged.

Syntax

Parameter

first: A forward iterator pointing the position of the first element in the range from which elements are being removed.

last: A forward iterator pointing the position one past the final element in the range from which elements are being removed.

pred: The unary predicate function which accepts an element as an argument that must be satisfied is the value of an element is to be replaced.

Return value

A forward iterator pointing the new end position (last) of the modified range or first element if first and last is equal.

Complexity

Complexity is linear in the range [first, last): Applies pred to each element, and possibly performs assignments on some of them.

Data races

The object in the range [first, last) are accessed and potentially modified.

Exception safety

This function throws an exception if any of pred, the element assignments or the operation on an iterator throws an exception.

Note: The invalid parameters cause an undefined behavior.

Example 1

Let's see the simple example to demonstrate the use of remove_if():

Output:

Original vector :  1 2 3 4 5 6 7 8 9 10
After remove_if : 2 4 6 8 10

Example 2

Let's see another simple example:

Output:

 Vector v1 is ( 4 7 7 7 0 5 7 1 6 9 3 7 8 2 ).
Vector v1 with elements satisfying greater6 removed is
 ( 4 0 5 1 6 3 2 1 6 9 3 7 8 2 ).
Vector v1 resized elements satisfying greater6 removed is
 ( 4 0 5 1 6 3 2 ).

Example 3

Let's see another simple example:

Output:

Vector : China    India    Korea    America    Australia    Pakistan    
Vector : China    India    Korea    Pakistan    

Example 4

Let's see another simple example to remove all spaces from a string by shifting all non-space characters to the left and then erasing the extra space.

Output:

Textwithsomespaces
Textwithsomewhitespaces

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