在迭代器中从std :: list中删除条目

Question

I am trying to remove elements in a list when a condition is met in a std::list . What I have read in the Reference about the return value of the erase function:

An iterator pointing to the element that followed the last element erased by the function call. This is the container end if the operation erased the last element in the sequence.

Member type iterator is a bidirectional iterator type that points to elements.

I have put this example together:

#include <string>
#include <list>
#include <iostream>

int main()
{
        typedef std::list<std::string> string_list_t;
        string_list_t list;
        list.push_back("test1");
        list.push_back("test2");
        list.push_back("test3");
        list.push_back("test4");
        list.push_back("test5");
        list.push_back("test6");
        list.push_back("test7");
        list.push_back("test8");

        for (string_list_t::iterator it = list.begin(); it != list.end(); ++it)
        {
                std::string &str = *it;
                std::cout << "Checking " << str << "..." << std::endl;
                if (str == "test4")
                {
                        std::cout << "Found test4!" << std::endl;
                }
                else
                {
                        it = list.erase(it);
                }
        }


    return 0;
}

It does not give me the expected output, instead it gives me:

Checking test1...
Checking test3...
Checking test5...
Checking test7...

Can someone help me figuring out what I understood wrong? Somehow it skips every second element...

Answer 1

You are skipping the element after the deleted one.

You should use either it = list.erase(it); or ++it , but not both.

Answer 2

When you erase an element from a std::list , do not increment the iterator returned by the std::list::erase method. You will not just skip the next element, you may just end up incrementing an end() iterator.

Change your loop to:

for (string_list_t::iterator it = list.begin(); it != list.end(); )
                                                                //^^ Not incremented
        {
                std::string &str = *it;
                std::cout << "Checking " << str << "..." << std::endl;
                if (str == "test4")
                {
                        std::cout << "Found test4!" << std::endl;
                        ++it;           //increment
                }
                else
                {
                        it = list.erase(it);
                }
        }

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