Asking for help, clarification, or responding to other answers. It seams like there should be a better way to do this using something like the erase(remove_if) paradigm but that works for unordered_map (I understand that the associative containers cannot be "re-ordered" hence the non-support of the remove_if algorithm). 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What is Catholic Church position regarding alcohol? Asking for help, clarification, or responding to other answers. Store the return value of erase(), which returns an iterator to the next element after the erased element (since c++11), and only increment if erase() was not called: In c++03 (and c++11 also) this could be accomplished with: Thanks for contributing an answer to Stack Overflow! Equivalent to To learn more, see our tips on writing great answers. It's still bad in that the OP is getting used to bad habits, and it's prone to error: e.g. Say you have some unordered map {a->x,b->y,c->z,d->r} and you have a reference to the second element b. You will be notified via email once the article is available for improvement. There are three type of erase functions supported by unordered_map : erasing by iterator: It takes an iterator as a parameter and erases the key and value present at that iterator. How to remove the a vector element from unordered_map, Deleting elements from vector inside unordered_map, Future society where tipping is mandatory. sci-fi novel from the 60s 70s or 80s about two civilizations in conflict that are from the same world. Thus the end () iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos . For example, say I have the following: std::unordered_map<size_t, my_obj*> map; my_obj *ptr = new my_obj (); map [5] = ptr; map.erase (5); // This calls a destructor on ptr. In Indiana Jones and the Last Crusade (1989), when does this shot of Sean Connery happen? Invalid operands to binary expression when using unordered_map? Making statements based on opinion; back them up with references or personal experience. What you shouldn't do is to try to the use object once erased. How do I write the reference mark symbol in TeX? No, the entire time the key is in the map, not just while you are calling map methods. privacy statement. However, I am getting the following error when I try to compile it: To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Not the answer you're looking for? Managing team members performance as Scrum Master. When a customer buys a product with a credit card, does the seller receive the money in installments or completely in one transaction? Returns a reference to the value that is mapped to a key equivalent to key, performing an insertion if such key does not already exist. Efficient way to delete a value from an unordered_map, when given just the value C++, Deleting pointer to object in unordered_map, Erasing elements from unordered_map in a loop, Delete value from unordered-map with 3 elements. rev2023.7.14.43533. Is it legal to not accept cash as a brick and mortar establishment in France? From lines 20 to 24, we erase the elements using the key and display the remaining elements. Algorithms and member functions are suggested over looping for efficiency when working with containers. And in its first 24 hours, more . Erasing element from multilevel unordered_map? Other references and iterators are not affected. Why can you not divide both sides of the equation, when working with exponential functions? Denys Fisher, of Spirograph fame, using a computer late 1976, early 1977, Find out all the different files from two different paths efficiently in Windows (with Python). std::unordered_map<Key,T,Hash,KeyEqual,Allocator>:: US Port of Entry would be LAX and destination is Boston. The erase members shall invalidate only iterators and references to the erased elements. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. To learn more, see our tips on writing great answers. I simply changed the const char* m_Str member declaration in CKey to std::wstring m_Str and that did it. Update The key does exist already. I can patch the code myself or you can send me a pull request if you prefer. What does it mean? std::unordered_map meets the requirements of Container, AllocatorAwareContainer, UnorderedAssociativeContainer . How to prevent a unordered_map of shared pointers from leaking? From lines 7 to 12, we initialize an unordered map with integer type keys and string type values. Also, I pass a copy of the string path to the user defined lambda function https://github.com/sol-prog/cpp17-filewatcher/blob/master/test_fs_watcher.cpp#L15 before erasing the map element. How should a time traveler be careful if they decide to stay and make a family in the past? Asking for help, clarification, or responding to other answers. Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood. unordered map - A non-loop efficient way to erase from unordered_map deque::clear() and deque::erase() in C++ STL, unordered_multiset erase() function in C++ STL, Erase Range of Elements From List Using Iterators in C++ STL, unordered_set erase() function in C++ STL, A-143, 9th Floor, Sovereign Corporate Tower, Sector-136, Noida, Uttar Pradesh - 201305, We use cookies to ensure you have the best browsing experience on our website. (This makes it possible to erase individual elements while iterating through the container.) c++ - unordered_map does not work - Stack Overflow set::erase in C++ STL - GeeksforGeeks If you can, you should use std::multimap and create a comparer where only TableID is involved. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Declaration. In lines 1 and 2, we import the required header files. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Other iterators and references are not invalidated. unordered_map does not work [closed] Ask Question Asked 8 years, 7 months ago Modified 8 years, 7 months ago Viewed 2k times 0 Closed. Will spinning a bullet really fast without changing its linear velocity make it do more damage? The C++ function std::unordered_map::equal() returns range of elements that matches specific key. Now, if you erase b while in a loop the reference to b will be invalidated but you should still be able to finish the loop without crashing. It seems that the only way to write truly portable C++ (or C) code is to test on all possible compiler/operating systems combinations. Temporary policy: Generative AI (e.g., ChatGPT) is banned, C++ map element doesn't get erased if I refer to it, sci-fi novel from the 60s 70s or 80s about two civilizations in conflict that are from the same world. Efficient way to delete a value from an unordered_map, when given just the value C++. There's no need of remove-if type "compaction", which suits std::vector 's use of contiguous memory. Where to start with a large crack the lock puzzle like this? How can I manually (on paper) calculate a Bitcoin public key from a private key? Making statements based on opinion; back them up with references or personal experience. We make use of First and third party cookies to improve our user experience. map erase() function in C++ STL - GeeksforGeeks How to draw a picture of a Periodic function? Asking for help, clarification, or responding to other answers. The iterator pos must be valid and dereferenceable. Is iMac FusionDrive->dual SSD migration any different from HDD->SDD upgrade from Time Machine perspective? You misinterpreted the docs. The shorter the message, the larger the prize. Other iterators and references are not invalidated. 1. setname.erase (position) 2. setname.erase (startingposition, endingposition) Parameters : Position of the element to be removed in the form of iterator or the range specified using start and end iterator. It's all single threaded, no concurrency so I cannot see how anything would change while the insertion or any map operation takes place. Is this color scheme another standard for RJ45 cable? Pros and cons of "anything-can-happen" UB versus allowing particular deviations from sequential progran execution, How to change what program Apple ProDOS 'starts' when booting. How is it that my map cannot manage the simplest of things and only keep one entry per key? The unordered_map::erase() removes some particular key-value pairs from the map. While everything was heap memory that remained in place the actual key value (not the hash or bucket position) changed from entry to entry. Why did the subject of conversation between Gingerbread Man and Lord Farquaad suddenly change? 2 Answers. Using std::map Wisely With Modern C++ - LinkedIn std::map<Key,T,Compare,Allocator>::erase - cppreference.com Co-author uses ChatGPT for academic writing - is it ethical? I changed it to std::map in my forked implementation and got AV at some point. Shows undefined behavior otherwise.Removing element from particular position. Specifying the iterator and specifying the range: In this case, it returns an iterator that immediately points to the position following the last elements erased in the unordered map. (Ep. Copyright 2023 Educative, Inc. All rights reserved. I've tried various implementations in Visual C++ 16.0 (the one that ships with Visual Studio 2010) and I'm getting all kinds of bugs with std::unordered_map. I'm trying to do my life easier by using the C++ API for map. You shouldn't reuse that iterator. BTW, have you tried compiling with /std:c++17 or /std:c++latest ? Yes, in fact, std::map::erase () returns a size_type which indicates the number of keys erased. Well ok, for a. What is the state of the art of splitting a binary file by size? How would life, that thrives on the magic of trees, survive in an area with limited trees? The text was updated successfully, but these errors were encountered: As far as I understand it, only the reference to the erased element is invalidated https://en.cppreference.com/w/cpp/container/unordered_map/erase so you can use a range for loop. From lines 26 to 32, we erase elements using a range and display the remaining elements. I do not believe they are to blame here. I'm trying to do my life easier by using the C++ API for map. unordered_multimap Class | Microsoft Learn Unordered_map provides following overloaded version of erase () that accepts a key by value and check if any element with given key exists and if yes then deletes that element. This is my old implementation: It works nicely, and do what I want: Managing team members performance as Scrum Master. Substituting my original implementation for this worked just fine. @Hurkyl And the iterator invalidation rules of containers are far from being brittle detail knowledge, it would be like not knowing the difference between C++ and ++C, oh wait. Unordered map erase method storing temporary variable, Deleting elements from vector inside unordered_map. How to draw a picture of a Periodic function? Agree To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Doping threaded gas pipes -- which threads are the "last" threads? I did some tests with Visual Studio 2019 and you were right the app crashed when a file was removed. Erasing element from multilevel unordered_map? Why? The test case is showing unexpected behaviour from the unordered_map class. rev2023.7.14.43533. These containers, and all other implementations of standard unordered associative containers, use an approach to its internal data structure design called closed addressing.Starting in Boost 1.81, Boost.Unordered also provides containers boost::unordered_flat_set and boost::unordered_flat_map, which use a different data structure strategy commonly known as open addressing and depart in a small . To learn more, see our tips on writing great answers. Distances of Fermat point from vertices of a triangle. C++ STL map::erase a non-existing key - Stack Overflow You have several solutions, one of these is O(n) (the solution that you have), another option, is to use another data structure, that meets your requiriments. 589). But as soon as I wrote down std::unordered_map<TurnStateEnum, . Is it legal to not accept cash as a brick and mortar establishment in France? Other references and iterators are not affected. "The order of the elements that are not erased is preserved (this makes it possible to erase individual elements while iterating through the container) " Thanks for contributing an answer to Stack Overflow! Other iterators and references are not invalidated." Say you have some unordered map {a->x,b->y,c->z,d->r} and you have a reference to the second element b. in your code you use paths_.erase(el.first); but that might invalidate the iterator. After using the operator= or copy constructor, erase of target object does not preform as expected - it affects both the source and target objects. Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood. 1,2) Removes the element at pos. Through the map.erase (begin, end) method I'm hoping to delete all the entries between [begin, end). Erasing elements from unordered_map in a loop. I think you should use a multimap or an unordered_multimap (hast_table). unordered_map maintains a linked list of nodes in each bucket, so it's cheap to erase them. rev2023.7.14.43533. For switching between the states I want to use an unordered_map with an enum as key and the state class as value. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Specifying the iterator: In this case, the function accepts only one parameter, i.e., the iterator, which points to the key-value pair to be erased. How to clear unordered_map of unordered_map in c++? Learn more. How to remove multiple items from unordered map while iterating over it? What Instagram's Threads app gets right and wrong as a Twitter Do I have to give the definition of CmpTabletKey to the iterator as well? I compiled with stdc++17, I may be wrong, but this is how I understand "References and iterators to the erased elements are invalidated. This means that you won't be able to insert values properly because equivalence would also not care about the .second. The reason is that the unordered_map store's key-value pair by taking the modulo of input value by a prime number and then stores it in a hash table. 79 void 80 ObjectFinder::flush (uint64_t tableId) { 81 82 RAMCLOUD_TEST_LOG . Learn in-demand tech skills in half the time. Result : Elements are removed from the specified position of the container. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Following is the declaration for std::unordered_map::equal . Temporary policy: Generative AI (e.g., ChatGPT) is banned, Erasing elements in std::tr1::unordered_map. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Where do 1-wire device (such as DS18B20) manufacturers obtain their addresses? Practice map::erase () is a built-in function in C++ STL that is used to erase elements from the container. Unordered map erase method storing temporary variable. The map is present in #include<unordered_map> header file. This article is being improved by another user right now. position Iterator to the element to remove. How to draw a picture of a Periodic function? An exercise in Data Oriented Design & Multi Threading in C++. In Indiana Jones and the Last Crusade (1989), when does this shot of Sean Connery happen? Iterator invalidation Notes The swap functions do not invalidate any of the iterators inside the container, but they do invalidate the iterator marking the end of the swap region. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Do you understand the range notation that you used? Other iterators and references are not invalidated." What does "rooting for my alt" mean in Stranger Things? Unordered_multimap Declaration. For which container type would this ever fail? Your compare operator is too specific, so it won't evaluate the equivalence of just the .first value. Sign in but it converts to native string only since GCC uses char/string for the representation then it works out of the box. hmmm there still might be a problem with this implementation. The Overflow #186: Do large language models know what theyre talking about? 2) Removes the elements in the range [first , last). Why is the Work on a Spring Independent of Applied Force? on VS 2017 it crashes, use case: run the app, add one file, wait till it appears in the console output as created, then delete that file and wait for the log message (app crashes) From the link by @Rob, C++11 has changed the return type from iterator to void. Which field is more rigorous, mathematics or philosophy? eraseiteratoriterator References and iterators to the erased elements are invalidated. ), in code there's a map of std::string and the path class has conversion operator: c++ map erase function not working properly with iterator OK, I've modified the code. How to use unordered_map efficiently in C++ - GeeksforGeeks Temporary policy: Generative AI (e.g., ChatGPT) is banned. How many witnesses testimony constitutes or transcends reasonable doubt? On Windows we use wstring to store the path in the native format, so that's why extra conversion is needed. 3) Removes all elements with the key value key. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Take the existing item and modify it. How terrifying is giving a conference talk? By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Which field is more rigorous, mathematics or philosophy? 9 min. I have tripled check that hash function and comparison function. Connect and share knowledge within a single location that is structured and easy to search. Ace your interviews with this free course, where you will practice confidently tackling behavioral interview questions. Create a fresh key-value pair. For the action callable object we could use filesystem::path, rather than string. @cached - you have accepted an answer that says your code above is OK. So which is it - does the code you asked the question about fail, or does it work? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The type of m_Records is either boost::unordered_map
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