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

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< cpp‎ | string‎ | basic string
 
 
 
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erase(std::basic_string)erase_if(std::basic_string)
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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;

Contents

[edit] 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). ​

[edit] Return value

The number of erased elements.

[edit] Complexity

Linear.

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for algorithm (1)

[edit] 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';
}

Output:

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

[edit] See also

removes elements satisfying specific criteria
(function template) [edit]