C++ List Iteration and erasing

Question

EDIT: This question refers specifically to std::lists - other similar questions on Stack Overflow refer to std::vectors

I'm using C++ and having trouble erasing an element from a std::list while iterating through it. I have a list of a custom class ('Objects' for the sake of this question), and my code looks like this:

for(auto i : Objects)
    if(i.EraseFlag == true)
        {
            i = Objects.erase(i);
        }

I'm getting the error: 'no matching function for call to std::list::erase(Object&)'

I believe this is the right way (as of C++11) to iterate through lists, erase an element and return an iterator that takes into account the erasure, but clearly I'm doing something wrong. Previously when using vectors I would use 'Objects.erase(Objects.begin() + i)' with i being an integer in a for loop, but given the access requirements of lists this won't work.

Help appreciated.

Thanks

You shouldn't be altering the sequence during the range based `for` loop. — PaulMcKenzie, Feb 27 '17 at 17:05
*I believe this is the right way (as of C++11) to iterate through lists, erase an element and return an iterator that takes into account the erasure,* -- Why erase things like this when you can do this using `erase / remove` idiom, where no loops are required? — PaulMcKenzie, Feb 27 '17 at 17:08
Thanks @PaulMcKenzie, remove_if looks like the right way to go about this - I've tried using your code, though I'm now getting an 'invalid use of auto' error - any ideas? — nathanburns, Feb 27 '17 at 17:50
@nathanburns I think you need to use either C++14 compilation, or try [this without auto](http://ideone.com/Ejqz95) — PaulMcKenzie, Feb 27 '17 at 19:47

score 1 · Accepted Answer · answered Feb 27 '17 at 17:14

1

Member function erase deals with iterators.

For such a task it would be correctly to use an ordinary for loop. For example

for ( auto it = Objects.begin(); it != Objects.end(); )
{
    if ( it->EraseFlag ) it = Objects.erase( it );
    else ++it;
}

Another approach is to use member function remove_if. For example

Objects.remove_if( []( const auto &value ) { return value.EraseFlag; } );

answered Feb 27 '17 at 17:14

Vlad from Moscow

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Thanks Vlad, your initial loop seems to work. It looks using remove_if would be the best practice way to do this, which you've also included so I'll mark this as the answer – nathanburns Feb 27 '17 at 17:55

C++ List Iteration and erasing

1 Answers1