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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>
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("Initially, cnt = ", cnt);
 
    std::erase(cnt, '3');
    print_container("After erase '3', cnt = ", cnt);
 
    auto erased = std::erase_if(cnt, [](char x) { return (x - '0') % 2 == 0; });
    print_container("After erase all even numbers, cnt = ", cnt);
    std::cout << "Erased even numbers: " << erased << '\n';
}

Output:

Initially, cnt = { 0 1 2 3 4 5 6 7 8 9 }
After erase '3', cnt = { 0 1 2 4 5 6 7 8 9 }
After erase all even numbers, cnt = { 1 5 7 9 }
Erased even numbers: 5

[edit] See also

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