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      std::mismatch

      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 InputIt1,class InputIt2>

      std::pair<InputIt1, InputIt2>
          mismatch( InputIt1 first1, InputIt1 last1,

                    InputIt2 first2);
      		 (1)(constexpr since C++20)
      template<class ExecutionPolicy,class ForwardIt1,class ForwardIt2>

      std::pair<ForwardIt1, ForwardIt2>
          mismatch( ExecutionPolicy&& policy,
                    ForwardIt1 first1, ForwardIt1 last1,

                    ForwardIt2 first2);
      		 (2)(since C++17)
      template<class InputIt1,class InputIt2,class BinaryPred>

      std::pair<InputIt1, InputIt2>
          mismatch( InputIt1 first1, InputIt1 last1,

                    InputIt2 first2, BinaryPred p);
      		 (3)(constexpr since C++20)
      template<class ExecutionPolicy,

               class ForwardIt1,class ForwardIt2,class BinaryPred>
      std::pair<ForwardIt1, ForwardIt2>
          mismatch( ExecutionPolicy&& policy,
                    ForwardIt1 first1, ForwardIt1 last1,

                    ForwardIt2 first2, BinaryPred p);
      		 (4)(since C++17)
      template<class InputIt1,class InputIt2>

      std::pair<InputIt1, InputIt2>
          mismatch( InputIt1 first1, InputIt1 last1,

                    InputIt2 first2, InputIt2 last2);
      		 (5)(since C++14)
      (constexpr since C++20)
      template<class ExecutionPolicy,class ForwardIt1,class ForwardIt2>

      std::pair<ForwardIt1, ForwardIt2>
          mismatch( ExecutionPolicy&& policy,
                    ForwardIt1 first1, ForwardIt1 last1,

                    ForwardIt2 first2, ForwardIt2 last2);
      		 (6)(since C++17)
      template<class InputIt1,class InputIt2,class BinaryPred>

      std::pair<InputIt1, InputIt2>
          mismatch( InputIt1 first1, InputIt1 last1,

                    InputIt2 first2, InputIt2 last2, BinaryPred p);
      		 (7)(since C++14)
      (constexpr since C++20)
      template<class ExecutionPolicy,

               class ForwardIt1,class ForwardIt2,class BinaryPred>
      std::pair<ForwardIt1, ForwardIt2>
          mismatch( ExecutionPolicy&& policy,
                    ForwardIt1 first1, ForwardIt1 last1,

                    ForwardIt2 first2, ForwardIt2 last2, BinaryPred p);
      		 (8)(since C++17)

      Returns a pair of iterators to the first mismatching of elements from[first1, last1) and a range starting fromfirst2:

      • For overloads(1-4), the second range hasstd::distance(first1, last1) elements.
      • For overloads(5-8), the second range is[first2, last2).
      1,5) Elements are compared usingoperator==.
      3,7) Elements are compared using the given binary predicatep.
      2,4,6,8) Same as(1,3,5,7), 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

      first1, last1 - the pair of iterators defining the firstrange of elements to compare
      first2, last2 - the pair of iterators defining the secondrange of elements to compare
      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 typesInputIt1 andInputIt2 can be dereferenced and then implicitly converted toType1 andType2 respectively.​

      Type requirements
      -
      InputIt1 must meet the requirements ofLegacyInputIterator.
      -
      InputIt2 must meet the requirements ofLegacyInputIterator.
      -
      ForwardIt1 must meet the requirements ofLegacyForwardIterator.
      -
      ForwardIt2 must meet the requirements ofLegacyForwardIterator.
      -
      BinaryPred must meet the requirements ofBinaryPredicate.

      [edit]Return value

      std::pair with iterators to the first two non-equal elements.

      Iflast1 is reached, the second iterator in the pair is thestd::distance(first1, last1)th iterator afterfirst2.

      For overloads(5-8), iflast2 is reached, the first iterator in the pair is thestd::distance(first2, last2)th iterator afterfirst1.

      [edit]Complexity

      Given\(\scriptsize N_1\)N1 asstd::distance(first1, last1) and\(\scriptsize N_2\)N2 asstd::distance(first2, last2):

      1,2) At most\(\scriptsize N_1\)N1 comparisons usingoperator==.
      3,4) At most\(\scriptsize N_1\)N1 applications of the predicatep.
      5,6) At most\(\scriptsize \min(N_1,N_2)\)min(N1,N2) comparisons usingoperator==.
      7,8) At most\(\scriptsize \min(N_1,N_2)\)min(N1,N2) 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

      mismatch (1)
      template<class InputIt1,class InputIt2>std::pair<InputIt1, InputIt2>    mismatch(InputIt1 first1, InputIt1 last1, InputIt2 first2){while(first1!= last1&&*first1==*first2)++first1,++first2; returnstd::make_pair(first1, first2);}
      mismatch (3)
      template<class InputIt1,class InputIt2,class BinaryPred>std::pair<InputIt1, InputIt2>    mismatch(InputIt1 first1, InputIt1 last1, InputIt2 first2, BinaryPred p){while(first1!= last1&& p(*first1,*first2))++first1,++first2; returnstd::make_pair(first1, first2);}
      mismatch (5)
      template<class InputIt1,class InputIt2>std::pair<InputIt1, InputIt2>    mismatch(InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2){while(first1!= last1&& first2!= last2&&*first1==*first2)++first1,++first2; returnstd::make_pair(first1, first2);}
      mismatch (7)
      template<class InputIt1,class InputIt2,class BinaryPred>std::pair<InputIt1, InputIt2>    mismatch(InputIt1 first1, InputIt1 last1,             InputIt2 first2, InputIt2 last2, BinaryPred p){while(first1!= last1&& first2!= last2&& p(*first1,*first2))++first1,++first2; returnstd::make_pair(first1, first2);}

      [edit]Example

      This program determines the longest substring that is simultaneously found at the very beginning of the given string and at the very end of it, in reverse order (possibly overlapping).

      Run this code
      #include <algorithm>#include <iostream>#include <string> std::string mirror_ends(conststd::string& in){returnstd::string(in.begin(),                       std::mismatch(in.begin(), in.end(), in.rbegin()).first);} int main(){std::cout<< mirror_ends("abXYZba")<<'\n'<< mirror_ends("abca")<<'\n'<< mirror_ends("aba")<<'\n';}

      Output:

      abaaba

      [edit]See also

      determines if two sets of elements are the same
      (function template)[edit]
      finds the first element satisfying specific criteria
      (function template)[edit]
      returnstrue if one range is lexicographically less than another
      (function template)[edit]
      searches for the first occurrence of a range of elements
      (function template)[edit]
      finds the first position where two ranges differ
      (algorithm function object)[edit]
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