std :: remove_if在返回的迭代器之后留下不应删除的元素

Question

我遇到了一个奇怪的问题：std::remove_if不能正确排列与指定谓词匹配的所有元素。例如，以下

#include <algorithm>
#include <ctime>
#include <cstdlib>
#include <iostream>
#include <vector>
#include <string>

struct Test {
    std::string name;
    double finalScore = 0;

    Test( double k ) : finalScore( k ) {}
};

int main() {
    std::srand( static_cast<unsigned int>( std::time( nullptr ) ) );

    std::vector<Test> vec;
    for ( unsigned i = 0; 50 != i; ++i ) {
        vec.push_back( Test( rand() % 10 + 1 ) );
    }

    auto rem = std::remove_if( vec.begin(), vec.end(), []( const Test &s ) {
        return s.finalScore < 5.0;
    } );

    std::cout << "item with below 5.0 finalScore count: "
              << ( vec.end() - rem ) << std::endl;
    std::cout << "items with below 5.0 finalScore: " << std::endl;

    for ( auto it = rem; vec.end() != it; ++it ) {
        std::cout << it->finalScore;

        if ( it->finalScore >= 5.0 ) {
            std::cout << " | incorrect; should not be present after rem.";
        }

        std::cout << std::endl;
    }

    return 0;
}

产生

item with below 5.0 finalScore count: 16
items with below 5.0 finalScore:
3
9 | incorrect; should not be present after rem.
8 | incorrect; should not be present after rem.
1
5 | incorrect; should not be present after rem.
6 | incorrect; should not be present after rem.
6 | incorrect; should not be present after rem.
7 | incorrect; should not be present after rem.
3
4
4
5 | incorrect; should not be present after rem.
6 | incorrect; should not be present after rem.
2
8 | incorrect; should not be present after rem.
10 | incorrect; should not be present after rem.

问题清晰可见：有些元素，谁的finalScore数据成员是>= 5，这是不应该的。预期结果应该与

类似

item with below 5.0 finalScore count: 6
items with below 5.0 finalScore:
3
1
3
4
4
2