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std:: erase, std:: erase_if (std::basic_string)

From cppreference.net

C++
Strings library
std::basic_string
Defined in header <string>
(1)
template < class CharT, class Traits, class Alloc, class U >

constexpr typename std:: basic_string < CharT, Traits, Alloc > :: size_type

erase ( std:: basic_string < CharT, Traits, Alloc > & c, const U & value ) ;
(since C++20)
(until C++26)
template < class CharT, class Traits, class Alloc, class U = CharT >

constexpr typename std:: basic_string < CharT, Traits, Alloc > :: size_type

erase ( std:: basic_string < CharT, Traits, Alloc > & c, const U & value ) ;
(since C++26)
template < class CharT, class Traits, class Alloc, class Pred >

constexpr typename std:: basic_string < CharT, Traits, Alloc > :: size_type

erase_if ( std:: basic_string < CharT, Traits, Alloc > & c, Pred pred ) ;
(2) (since C++20)
1) Erases all elements that compare equal to value from the container c . Equivalent to auto it = std :: remove ( c. begin ( ) , c. end ( ) , value ) ;
auto r = c. end ( ) - it ;
c. erase ( it, c. end ( ) ) ;
return r ; .
2) Erases all elements that satisfy the predicate pred from the container c . Equivalent to auto it = std:: remove_if ( c. begin ( ) , c. end ( ) , pred ) ;
auto r = c. end ( ) - it ;
c. erase ( it, c. end ( ) ) ;
return r ; .

Contents

Parameters

c - container from which to erase
value - value to be removed
pred - unary predicate which returns ​ true if the element should be erased.

The expression pred ( v ) must be convertible to bool for every argument v of type (possibly const) CharT , regardless of value category , and must not modify v . Thus, a parameter type of CharT & is not allowed , nor is CharT unless for CharT a move is equivalent to a copy (since C++11) . ​

Return value

The number of erased elements.

Complexity

Linear.

Notes

Feature-test macro Value Std Feature
__cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for std::erase

Example

Run this code 
#include <iomanip>
#include <iostream>
#include <string>
int main()
{
    std::string word{"startling"};
    std::cout << "Initially, word = " << std::quoted(word) << '\n';
    std::erase(word, 'l');
    std::cout << "After erase 'l': " << std::quoted(word) << '\n';
    auto erased = std::erase_if(word, [](char x)
    {
        return x == 'a' or x == 'r' or x == 't';
    });
    std::cout << "After erase all 'a', 'r', and 't': " << std::quoted(word) << '\n';
    std::cout << "Erased symbols count: " << erased << '\n';
#if __cpp_lib_algorithm_default_value_type
    std::erase(word, {'g'});
    std::cout << "After erase {'g'}: " << std::quoted(word) << '\n';
#endif
}

Possible output: 

Initially, word = "startling"
After erase 'l', word = "starting"
After erase all 'a', 'r', and 't': "sing"
Erased symbols count: 4
After erase {'g'}: "sin"

See also

removes elements satisfying specific criteria
(function template)
(C++20) (C++20)
removes elements satisfying specific criteria
(algorithm function object)