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Difference between revisions of "cpp/algorithm/mismatch"

From cppreference.com
< cpp‎ | algorithm
m (Text replace - "{{returns}}" to "===Return value===")
m (Mathjax update.)
 
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{{cpp/title|mismatch}}
 
{{cpp/title|mismatch}}
−
{{cpp/algorithm/sidebar}}
+
{{cpp/algorithm/navbar}}
−
{{ddcl list begin}}
+
{{dcl begin}}
−
{{ddcl list header | algorithm}}
+
{{dcl header|algorithm}}
−
{{ddcl list item | num=1 |
+
{{dcla|num=1|notes={{mark constexpr since c++20}}|
−
template< class InputIterator1, class InputIterator2 >
+
template< class InputIt1, class InputIt2 >
−
std::pair< InputIterator1, InputIterator2 >
+
std::pair<InputIt1, InputIt2>
−
     mismatch( InputIterator1 first1,
+
     mismatch( InputIt1 first1, InputIt1 last1,
−
              InputIterator1 last1,
+
               InputIt2 first2 );
−
               InputIterator2 first2 );
+
 
}}
 
}}
−
{{ddcl list item | num=2 |
+
{{dcl|num=2|since=c++17|
−
template< class InputIterator1, class InputIterator2, class BinaryPredicate >
+
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >
−
std::pair< InputIterator1, InputIterator2 >
+
std::pair<ForwardIt1, ForwardIt2>
−
     mismatch( InputIterator1 first1,
+
     mismatch( ExecutionPolicy&& policy,
−
               InputIterator1 last1,
+
               ForwardIt1 first1, ForwardIt1 last1,
−
               InputIterator2 first2,
+
               ForwardIt2 first2 );
−
              BinaryPredicate p );
+
 
}}
 
}}
−
{{ddcl list end}}
+
{{dcla|num=3|notes={{mark constexpr since c++20}}|
 +
template< class InputIt1, class InputIt2, class BinaryPred >
 +
std::pair<InputIt1, InputIt2>
 +
    mismatch( InputIt1 first1, InputIt1 last1,
 +
              InputIt2 first2, BinaryPred p );
 +
}}
 +
{{dcl|num=4|since=c++17|
 +
template< class ExecutionPolicy,
 +
          class ForwardIt1, class ForwardIt2, class BinaryPred >
 +
std::pair<ForwardIt1, ForwardIt2>
 +
    mismatch( ExecutionPolicy&& policy,
 +
              ForwardIt1 first1, ForwardIt1 last1,
 +
              ForwardIt2 first2, BinaryPred p );
 +
}}
 +
{{dcla|num=5|since=c++14|notes={{mark constexpr since c++20}}|
 +
template< class InputIt1, class InputIt2 >
 +
std::pair<InputIt1, InputIt2>
 +
    mismatch( InputIt1 first1, InputIt1 last1,
 +
              InputIt2 first2, InputIt2 last2 );
 +
}}
 +
{{dcl|num=6|since=c++17|
 +
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >
 +
std::pair<ForwardIt1, ForwardIt2>
 +
    mismatch( ExecutionPolicy&& policy,
 +
              ForwardIt1 first1, ForwardIt1 last1,
 +
              ForwardIt2 first2, ForwardIt2 last2 );
 +
}}
 +
{{dcla|num=7|since=c++14|notes={{mark constexpr since c++20}}|
 +
template< class InputIt1, class InputIt2, class BinaryPred >
 +
std::pair<InputIt1, InputIt2>
 +
    mismatch( InputIt1 first1, InputIt1 last1,
 +
              InputIt2 first2, InputIt2 last2, BinaryPred p );
 +
}}
 +
{{dcl|num=8|since=c++17|
 +
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 );
 +
}}
 +
{{dcl end}}
 +
 
 +
Returns a pair of iterators to the first mismatching of elements from {{range|first1|last1}} and a range starting from {{c|first2}}:
 +
* For overloads {{v|1-4}}, the second range has {{c|std::distance(first1, last1)}} elements.
 +
* For overloads {{v|5-8}}, the second range is {{range|first2|last2}}.
 +
:* If {{c|std::distance(first1, last1)}} and {{c|std::distance(first2, last2)}} are different, the comparison stops when {{c|last1}} or {{c|last2}} is reached.
 +
 
 +
@1,5@ Elements are compared using {{c/core|1=operator==}}.
 +
@3,7@ Elements are compared using the given binary predicate {{c|p}}.
  
−
Returns the first mismatching pair of elements from two ranges: one defined by {{tt|[first1, last1)}} and another starting at {{tt|first2}}. The first version of the function uses {{tt|operator{{==}}}} to compare the elements, the second version uses the given binary predicate {{tt|p}}.
+
@2,4,6,8@ Same as {{v|1,3,5,7}}, but executed according to {{c|policy}}.
 +
@@ {{cpp/algorithm/parallel overload precondition|plural=yes}}
  
−
<!-- ======== -->
 
 
===Parameters===
 
===Parameters===
−
{{param list begin}}
+
{{par begin}}
−
{{param list item | first1, last1 | the first range of the elements}}
+
{{par|first1, last1|the first range of the elements}}
−
{{param list item | first2 | the beginning of the second range of the elements}}
+
{{par|first2, last2|the second range of the elements}}
−
{{param list pred2 eq | p | p1=InputIterator1 | p2=InputIterator2}}
+
{{par exec pol}}
−
{{param list end}}
+
{{par pred2 eq|p|p1=InputIt1|p2=InputIt2}}
 +
{{par hreq}}
 +
{{par req named|InputIt1|InputIterator}}
 +
{{par req named|InputIt2|InputIterator}}
 +
{{par req named|ForwardIt1|ForwardIterator}}
 +
{{par req named|ForwardIt2|ForwardIterator}}
 +
{{par req named|BinaryPred|BinaryPredicate}}
 +
{{par end}}
  
−
<!-- ======== -->
 
 
===Return value===
 
===Return value===
 +
{{lc|std::pair}} with iterators to the first two non-equal elements.
  
−
{{cpp|std::pair}} with iterators to the first two non-equivalent elements, or, if no different elements found, pair with {{tt|last1}} and the corresponding iterator from the second range.
+
If {{c|last1}} is reached, the second iterator in the pair is the {{c|std::distance(first1, last1)}}{{su|b=th}} iterator after {{c|first2}}.
  
−
<!-- ======== -->
+
For overloads {{v|5-8}}, if {{c|last2}} is reached, the first iterator in the pair is the {{c|std::distance(first2, last2)}}{{su|b=th}} iterator after {{c|first1}}.
−
{{complex}}
+
  
−
linear in the distance between {{tt|first1}} and {{tt|last1}}
+
===Complexity===
 +
Given {{mathjax-or|\(\scriptsize N_1\)|N{{su|b=1}}}} as {{c|std::distance(first1, last1)}} and {{mathjax-or|\(\scriptsize N_2\)|N{{su|b=2}}}} as {{c|std::distance(first2, last2)}}:
 +
@1,2@ At most {{mathjax-or|\(\scriptsize N_1\)|N{{su|b=1}}}} comparisons using {{c/core|1=operator==}}.
 +
@3,4@ At most {{mathjax-or|\(\scriptsize N_1\)|N{{su|b=1}}}} applications of the predicate {{c|p}}.
 +
@5,6@ At most {{mathjax-or|\(\scriptsize \min(N_1,N_2)\)|min(N{{su|b=1}},N{{su|b=2}})}} comparisons using {{c/core|1=operator==}}.
 +
@7,8@ At most {{mathjax-or|\(\scriptsize \min(N_1,N_2)\)|min(N{{su|b=1}},N{{su|b=2}})}} applications of the predicate {{c|p}}.
  
−
<!-- ======== -->
+
===Exceptions===
−
{{eq fun}}
+
{{cpp/algorithm/parallel exceptions reporting behavior|singular=no}}
−
{{eq fun cpp
+
 
−
| 1=
+
===Possible implementation===
−
template<class InputIterator1, class InputIterator2>
+
{{eq impl
−
std::pair<InputIterator1, InputIterator2>
+
|title1=mismatch (1)|ver1=1|1=
−
     mismatch(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2)
+
template<class InputIt1, class InputIt2>
 +
std::pair<InputIt1, InputIt2>
 +
     mismatch(InputIt1 first1, InputIt1 last1, InputIt2 first2)
 
{
 
{
−
     for (; first1 != last1; ++first1, ++first2) {
+
     while (first1 != last1 && *first1 == *first2)
−
        if (*first1 != *first2) {
+
        ++first1, ++first2;
−
            return std::make_pair(first1, first2);
+
      
−
        }
+
−
     }
+
 
     return std::make_pair(first1, first2);
 
     return std::make_pair(first1, first2);
 
}
 
}
−
| 2=
+
|title2=mismatch (3)|ver2=3|2=
−
template<class InputIterator1, class InputIterator2, class BinaryPredicate>
+
template<class InputIt1, class InputIt2, class BinaryPred>
−
std::pair<InputIterator1, InputIterator2>
+
std::pair<InputIt1, InputIt2>
−
     mismatch(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, BinaryPredicate p)
+
     mismatch(InputIt1 first1, InputIt1 last1, InputIt2 first2, BinaryPred p)
 
{
 
{
−
     for (; first1 != last1; ++first1, ++first2) {
+
     while (first1 != last1 && p(*first1, *first2))
−
        if (!p(*first1, *first2)) {
+
        ++first1, ++first2;
−
            return std::make_pair(first1, first2);
+
   
−
        }
+
    return std::make_pair(first1, first2);
−
     }
+
}
 +
|title3=mismatch (5)|ver3=5|3=
 +
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;
 +
   
 +
    return std::make_pair(first1, first2);
 +
}
 +
|title4=mismatch (7)|ver4=7|4=
 +
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;
 +
      
 
     return std::make_pair(first1, first2);
 
     return std::make_pair(first1, first2);
 
}
 
}
 
}}
 
}}
  
−
<!-- ======== -->
 
 
===Example===
 
===Example===
 +
{{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).
 +
|code=
 +
#include <algorithm>
 +
#include <iostream>
 +
#include <string>
 +
 +
std::string mirror_ends(const std::string& in)
 +
{
 +
    return std::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=
 +
ab
 +
a
 +
aba
 +
}}
  
−
{{todo}}
+
===See also===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/algorithm/dsc equal}}
 +
{{dsc inc|cpp/algorithm/dsc find}}
 +
{{dsc inc|cpp/algorithm/dsc lexicographical_compare}}
 +
{{dsc inc|cpp/algorithm/dsc search}}
 +
{{dsc inc|cpp/algorithm/ranges/dsc mismatch}}
 +
{{dsc end}}
  
−
<!-- ======== -->
+
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
−
{{see also}}
+
−
{{dcl list begin}}
+
−
{{dcl list template | cpp/algorithm/dcl list equal}}
+
−
{{dcl list template | cpp/algorithm/dcl list find}}
+
−
{{dcl list template | cpp/algorithm/dcl list lexicographical_compare}}
+
−
{{dcl list template | cpp/algorithm/dcl list search}}
+
−
{{dcl list end}}
+

Latest revision as of 01:37, 3 April 2024

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)
mismatch

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(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
(C++20)
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 from first2:

  • For overloads (1-4), the second range has std::distance(first1, last1) elements.
  • For overloads (5-8), the second range is [first2, last2).
  • If std::distance(first1, last1) and std::distance(first2, last2) are different, the comparison stops when last1 or last2 is reached.
1,5) Elements are compared using operator==.
3,7) Elements are compared using the given binary predicate p.
2,4,6,8) Same as (1,3,5,7), but executed according to policy.
These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)

Contents

[edit] Parameters

first1, last1 - the first range of the elements
first2, last2 - the second range of the elements
policy - the execution policy to use. See execution policy for details.
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 have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).
The types Type1 and Type2 must be such that objects of types InputIt1 and InputIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively. ​

Type requirements
-
InputIt1 must meet the requirements of LegacyInputIterator.
-
InputIt2 must meet the requirements of LegacyInputIterator.
-
ForwardIt1 must meet the requirements of LegacyForwardIterator.
-
ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
BinaryPred must meet the requirements of BinaryPredicate.

[edit] Return value

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

If last1 is reached, the second iterator in the pair is the std::distance(first1, last1)th iterator after first2.

For overloads (5-8), if last2 is reached, the first iterator in the pair is the std::distance(first2, last2)th iterator after first1.

[edit] Complexity

Given N1 as std::distance(first1, last1) and N2 as std::distance(first2, last2):

1,2) At most N1 comparisons using operator==.
3,4) At most N1 applications of the predicate p.
5,6) At most min(N1,N2) comparisons using operator==.
7,8) At most min(N1,N2) applications of the predicate p.

[edit] Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, 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;
 
    return std::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;
 
    return std::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;
 
    return std::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;
 
    return std::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(const std::string& in)
{
    return std::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: 

ab
a
aba

[edit] See also

 determines if two sets of elements are the same
(function template) [edit]
(C++11)
 finds the first element satisfying specific criteria
(function template) [edit]
returns true if one range is lexicographically less than another
(function template) [edit]
searches for the first occurrence of a range of elements
(function template) [edit]
(C++20)
 finds the first position where two ranges differ
(niebloid)[edit]
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