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      std::find_first_of

      From cppreference.com
      <cpp‎ |algorithm
       
       
      Algorithm library
      Constrained algorithms and algorithms on ranges(C++20)
      Constrained algorithms, e.g.ranges::copy,ranges::sort, ...
      Execution policies(C++17)
      Sorting and related operations
      Partitioning operations
      Sorting operations
      Binary search operations
      (on partitioned ranges)
      Set operations (on sorted ranges)
      Merge operations (on sorted ranges)
      Heap operations
      Minimum/maximum operations
      (C++11)
      (C++17)
      Lexicographical comparison operations
      Permutation operations
      C library
      Numeric operations
      Operations on uninitialized memory
       
      Defined in header<algorithm>
      template<class InputIt,class ForwardIt>

      InputIt find_first_of( InputIt first, InputIt last,

                             ForwardIt s_first, ForwardIt s_last);
      		 (1)(constexpr since C++20)
      template<class ExecutionPolicy,class ForwardIt1,class ForwardIt2>

      ForwardIt1 find_first_of( ExecutionPolicy&& policy,
                                ForwardIt1 first, ForwardIt1 last,

                                ForwardIt2 s_first, ForwardIt2 s_last);
      		 (2)(since C++17)
      template<class InputIt,class ForwardIt,class BinaryPred>

      InputIt find_first_of( InputIt first, InputIt last,
                             ForwardIt s_first, ForwardIt s_last,

                             BinaryPred p);
      		 (3)(constexpr since C++20)
      template<class ExecutionPolicy,

               class ForwardIt1,class ForwardIt2,class BinaryPred>
      ForwardIt1 find_first_of( ExecutionPolicy&& policy,
                                ForwardIt1 first, ForwardIt last,
                                ForwardIt2 s_first, ForwardIt2 s_last,

                                BinaryPred p);
      		 (4)(since C++17)

      Searches the range[first, last) for any of the elements in the range[s_first, s_last).

      1) Elements are compared usingoperator==.
      3) Elements are compared using the given binary predicatep.
      2,4) Same as(1,3), but executed according topolicy.
      These overloads participate in overload resolution only if all following conditions are satisfied:

      std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> istrue.

      		(until C++20)

      std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> istrue.

      		(since C++20)

      Contents

      [edit]Parameters

      first, last - the pair of iterators defining therange of elements to examine
      s_first, s_last - the pair of iterators defining therange of elements to search for
      policy - theexecution policy to use
      p - binary predicate which returns ​true if the elements should be treated as equal.

      The signature of the predicate function should be equivalent to the following:

       bool pred(const Type1&a,const Type2&b);

      While the signature does not need to haveconst&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const)Type1 andType2 regardless ofvalue category (thus,Type1& is not allowed, nor isType1 unless forType1 a move is equivalent to a copy(since C++11)).
      The typesType1 andType2 must be such that objects of typesForwardIt1 andForwardIt2 can be dereferenced and then implicitly converted toType1 andType2 respectively.​

      Type requirements
      -
      InputIt must meet the requirements ofLegacyInputIterator.
      -
      ForwardIt must meet the requirements ofLegacyForwardIterator.
      -
      ForwardIt1 must meet the requirements ofLegacyForwardIterator.
      -
      ForwardIt2 must meet the requirements ofLegacyForwardIterator.
      -
      BinaryPred must meet the requirements ofBinaryPredicate.

      [edit]Return value

      Iterator to the first element in the range[first, last) that is equal to an element from the range[s_first, s_last).

      If[s_first, s_last) is empty or if no such element is found,last is returned.

      [edit]Complexity

      Given\(\scriptsize N\)N asstd::distance(first, last) and\(\scriptsize S\)S asstd::distance(s_first, s_last):

      1,2) At most\(\scriptsize N\cdot S\)N·S comparisons usingoperator==.
      3,4) At most\(\scriptsize N\cdot S\)N·S applications of the predicatep.

      [edit]Exceptions

      The overloads with a template parameter namedExecutionPolicy report errors as follows:

      • If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard policies,std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined.
      • If the algorithm fails to allocate memory,std::bad_alloc is thrown.

      [edit]Possible implementation

      find_first_of (1)
      template<class InputIt,class ForwardIt>InputIt find_first_of(InputIt first, InputIt last,                      ForwardIt s_first, ForwardIt s_last){for(; first!= last;++first)for(ForwardIt it= s_first; it!= s_last;++it)if(*first==*it)return first;return last;}
      find_first_of (3)
      template<class InputIt,class ForwardIt,class BinaryPred>InputIt find_first_of(InputIt first, InputIt last,                      ForwardIt s_first, ForwardIt s_last,                      BinaryPred p){for(; first!= last;++first)for(ForwardIt it= s_first; it!= s_last;++it)if(p(*first,*it))return first;return last;}

      [edit]Example

      The following code searches for any of specified integers in a vector of integers:

      Run this code
      #include <algorithm>#include <iostream>#include <vector> auto print_sequence=[](constauto id,constauto& seq,int pos=-1){std::cout<< id<<"{ ";for(int i{};autoconst& e: seq){constbool mark{i== pos};std::cout<<(i++?", ":"");std::cout<<(mark?"[ ":"")<< e<<(mark?" ]":"");}std::cout<<" }\n";}; int main(){conststd::vector<int> v{0,2,3,25,5};constauto t1={19,10,3,4};constauto t2={1,6,7,9}; auto find_any_of=[](constauto& v,constauto& t){constauto result= std::find_first_of(v.begin(), v.end(),                                               t.begin(), t.end());if(result== v.end()){std::cout<<"No elements of v are equal to any element of ";            print_sequence("t = ", t);            print_sequence("v = ", v);}else{constauto pos=std::distance(v.begin(), result);std::cout<<"Found a match ("<<*result<<") at position "<< pos;            print_sequence(", where t = ", t);            print_sequence("v = ", v, pos);}};     find_any_of(v, t1);    find_any_of(v, t2);}

      Output:

      Found a match (3) at position 2, where t = { 19, 10, 3, 4 }v = { 0, 2, [ 3 ], 25, 5 }No elements of v are equal to any element of t = { 1, 6, 7, 9 }v = { 0, 2, 3, 25, 5 }

      [edit]Defect reports

      The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

      DRApplied toBehavior as publishedCorrect behavior
      LWG 576C++98first andlast needed to beLegacyForwardIteratorsthey only need to be
      LegacyInputIterators
      LWG 1205C++98the return value was unclear if[s_first, s_last) is emptyreturnslast in this case

      [edit]See also

      finds the first element satisfying specific criteria
      (function template)[edit]
      searches for any one of a set of elements
      (algorithm function object)[edit]
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