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

From cppreference.com
< cpp‎ | string‎ | basic string
 
 
 
std::basic_string
Non-member functions
erase(std::basic_string)erase_if(std::basic_string)
(C++20)(C++20)
I/O
Comparison
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Numeric conversion (C++11)
Helper classes
Deduction guides(C++17)
 
Defined in header <string>
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);
(1) (since C++20)
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. Equivalent to
auto it = std::remove(c.begin(), c.end(), value);
auto r = std::distance(it, c.end());
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 = std::distance(it, c.end());
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] Example

#include <iostream>
#include <numeric>
#include <string_view>
#include <string>
 
void print_container(std::string_view comment, const std::string& c)
{
    std::cout << comment;
    for (auto x : c) {
        std::cout << x << ' ';
    }
    std::cout << '\n';
}
 
int main()
{
    std::string cnt(10, ' ');
    std::iota(cnt.begin(), cnt.end(), '0');
    print_container("Init:\n", cnt);
 
    std::erase(cnt, '3');
    print_container("Erase '3':\n", cnt);
 
    auto erased = std::erase_if(cnt, [](char x) { return (x - '0') % 2 == 0; });
    print_container("Erase all even numbers:\n", cnt);
    std::cout << "In all " << erased << " even numbers were erased.\n";
}

Output:

Init:
0 1 2 3 4 5 6 7 8 9 
Erase '3':
0 1 2 4 5 6 7 8 9 
Erase all even numbers:
1 5 7 9
In all 5 even numbers were erased.

[edit] See also

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