How to search for an element in an stl list

Question

Is there a find   function for list as there was in vector   Is there a way to do that in list

User · Answer

No  find   method is not a member of std  list  Instead  use std  find from  lt algorithm gt       std    list  lt  int  gt  l      std    list  lt  int  gt     iterator pos       l push back 1       l push back 2       l push back 3       l push back 4       l push back 5       l push back 6        int elem   3         pos   find l begin     l end     elem       if pos    l end             std    cout  lt  lt   Element is present    lt  lt std    endl      else         std    cout  lt  lt   Element is not present    lt  lt std    endl

User · Answer

You use std  find from  lt algorithm gt   which works equally well for std  list and std  vector  std  vector does not have its own search find function    include  lt list gt   include  lt algorithm gt   int main         std  list lt int gt  ilist      ilist push back 1       ilist push back 2       ilist push back 3        std  list lt int gt   iterator findIter   std  find ilist begin    ilist end    1       Note that this works for built-in types like int as well as standard library types like std  string by default because they have operator   provided for them  If you are using using std  find on a container of a user-defined type  you should overload operator   to allow std  find to work properly  EqualityComparable concept

User · Answer

No  not directly in the std  list template itself  You can however use std  find algorithm like that  std  list lt int gt  my list        int some value   12  std  list lt int gt   iterator iter   std  find  my list begin    my list end    some value      now variable iter either represents valid iterator pointing to the found element     or it will be equal to my list end

User · Answer

Besides using std  find  from algorithm   you can also use std  find if  which is  IMO  better than std  find   or other find algorithm from this list   include  lt list gt   include  lt algorithm gt   include  lt iostream gt   int main         std  list lt int gt  myList  5  19  34  3  33              auto it   std  find if  std  begin  myList                                std  end  myList                                  amp    const int v    return 0      v   17                      if   myList end      it                 std  cout  lt  lt   quot item not found quot   lt  lt  std  endl            else               const int pos   std  distance  myList begin    it     1          std  cout  lt  lt   quot item divisible by 17 found at position  quot   lt  lt  pos  lt  lt  std  endl

User · Answer

What you can do and what you should do are different matters   If the list is very short  or you are only ever going to call find once then use the linear approach above   However linear-search is one of the biggest evils I find in slow code  and consider using an ordered collection  set or multiset if you allow duplicates   If you need to keep a list for other reasons eg using an LRU technique or you need to maintain the insertion order or some other order  create an index for it  You can actually do that using a std  set of the list iterators  or multiset  although you need to maintain this any time your list is modified

[c++] How to search for an element in an stl list?

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