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std::erase, std::erase_if(std::basic_string) - cppreference.com

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Defined in header <string>

(1)

template< class CharT, class Traits, class Alloc, class U > constexpr 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 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 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. 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. Equivalent to 

auto it = std::remove_if(c.begin(), c.end(), pred);
auto r = c.end() - it;
c.erase(it, c.end());
return r;

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 algorithm (1)

Example

#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