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Difference between revisions of "cpp/algorithm/min element"

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< cpp‎ | algorithm
m (→‎See also: + std::ranges version)
(Added LWG issue #212 DR (part 2/2).)
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{{cpp/algorithm/navbar}}
 
{{cpp/algorithm/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
−
{{dcl header | algorithm}}
+
{{dcl header|algorithm}}
−
{{dcl rev multi | num=1
+
{{dcl rev multi|num=1
−
| until1=c++17 | dcl1=
+
|until1=c++17|dcl1=
 
template< class ForwardIt >  
 
template< class ForwardIt >  
 
ForwardIt min_element( ForwardIt first, ForwardIt last );
 
ForwardIt min_element( ForwardIt first, ForwardIt last );
−
| dcl2=
+
|dcl2=
 
template< class ForwardIt >  
 
template< class ForwardIt >  
 
constexpr ForwardIt min_element( ForwardIt first, ForwardIt last );
 
constexpr ForwardIt min_element( ForwardIt first, ForwardIt last );
 
}}
 
}}
−
{{dcl | since=c++17 | num= 2 |1=
+
{{dcl|since=c++17|num=2|1=
 
template< class ExecutionPolicy, class ForwardIt >  
 
template< class ExecutionPolicy, class ForwardIt >  
 
ForwardIt min_element( ExecutionPolicy&& policy,  
 
ForwardIt min_element( ExecutionPolicy&& policy,  
 
                       ForwardIt first, ForwardIt last );
 
                       ForwardIt first, ForwardIt last );
 
}}
 
}}
−
{{dcl rev multi | num=3
+
{{dcl rev multi|num=3
−
| until1=c++17 | dcl1=
+
|until1=c++17|dcl1=
 
template< class ForwardIt, class Compare >
 
template< class ForwardIt, class Compare >
 
ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );
 
ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );
−
| dcl2=
+
|dcl2=
 
template< class ForwardIt, class Compare >
 
template< class ForwardIt, class Compare >
−
constexpr ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );
+
constexpr ForwardIt min_element( ForwardIt first, ForwardIt last,
 +
                                Compare comp );
 
}}
 
}}
−
{{dcl | since=c++17 | num= 4 |1=
+
{{dcl|since=c++17|num=4|1=
 
template< class ExecutionPolicy, class ForwardIt, class Compare >
 
template< class ExecutionPolicy, class ForwardIt, class Compare >
 
ForwardIt min_element( ExecutionPolicy&& policy,  
 
ForwardIt min_element( ExecutionPolicy&& policy,  
Line 34: Line 35:
  
 
@1@ Elements are compared using {{tt|operator<}}.
 
@1@ Elements are compared using {{tt|operator<}}.
−
@3@ Elements are compared using the given binary comparison function {{tt|comp}}.
+
@3@ Elements are compared using the given binary comparison function {{c|comp}}.
−
@2,4@ Same as {{v|1,3}}, but executed according to {{tt|policy}}. {{cpp/algorithm/parallel overload precondition|plural=true}}
+
@2,4@ Same as {{v|1,3}}, but executed according to {{c|policy}}. {{cpp/algorithm/parallel overload precondition|plural=true}}
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | first, last | forward iterators defining the range to examine}}
+
{{par|first, last|forward iterators defining the range to examine}}
 
{{par exec pol}}
 
{{par exec pol}}
−
{{par cmp | comp | p1=ForwardIt | {{tt|a}} is ''less'' than {{tt|b}}}}  
+
{{par cmp|comp|p1=ForwardIt|{{tt|a}} is ''less'' than {{tt|b}}}}  
 
{{par hreq}}
 
{{par hreq}}
−
{{par req named | ForwardIt | ForwardIterator}}
+
{{par req named|ForwardIt|ForwardIterator}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
Iterator to the smallest element in the range {{tt|[first, last)}}. If several elements in the range are equivalent to the smallest element, returns the iterator to the first such element. Returns {{tt|last}} if the range is empty.
+
Iterator to the smallest element in the range {{tt|[first, last)}}. If several elements in the range are equivalent to the smallest element, returns the iterator to the first such element. Returns {{c|last}} if the range is empty.
  
 
===Complexity===
 
===Complexity===
−
Exactly {{math|max(N-1,0)}} comparisons, where {{c|N {{=}} std::distance(first, last)}}.
+
Exactly {{math|max(N-1,0)}} comparisons, where {{c|1=N = std::distance(first, last)}}.
  
 
===Exceptions===
 
===Exceptions===
−
{{cpp/algorithm/parallel_exceptions_reporting_behavior|singular=no}}
+
{{cpp/algorithm/parallel exceptions reporting behavior|singular=no}}
  
 
===Possible implementation===
 
===Possible implementation===
 
{{eq fun
 
{{eq fun
−
| 1=
+
|1=
 
template<class ForwardIt>
 
template<class ForwardIt>
 
ForwardIt min_element(ForwardIt first, ForwardIt last)
 
ForwardIt min_element(ForwardIt first, ForwardIt last)
 
{
 
{
−
     if (first == last) return last;
+
     if (first == last)
 +
        return last;
  
 
     ForwardIt smallest = first;
 
     ForwardIt smallest = first;
 
     ++first;
 
     ++first;
−
     for (; first != last; ++first) {
+
   
−
         if (*first < *smallest) {
+
     for (; first != last; ++first)
 +
         if (*first < *smallest)
 
             smallest = first;
 
             smallest = first;
−
        }
+
      
−
     }
+
 
     return smallest;
 
     return smallest;
 
}
 
}
−
| 2=
+
|2=
 
template<class ForwardIt, class Compare>
 
template<class ForwardIt, class Compare>
 
ForwardIt min_element(ForwardIt first, ForwardIt last, Compare comp)
 
ForwardIt min_element(ForwardIt first, ForwardIt last, Compare comp)
 
{
 
{
−
     if (first == last) return last;
+
     if (first == last)
 +
        return last;
 
      
 
      
 
     ForwardIt smallest = first;
 
     ForwardIt smallest = first;
 
     ++first;
 
     ++first;
−
     for (; first != last; ++first) {
+
   
−
         if (comp(*first, *smallest)) {
+
     for (; first != last; ++first)
 +
         if (comp(*first, *smallest))
 
             smallest = first;
 
             smallest = first;
−
        }
+
      
−
     }
+
 
     return smallest;
 
     return smallest;
 
}
 
}
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===Example===
 
===Example===
 
{{example
 
{{example
−
|
+
|
−
| code=
+
|code=
 
#include <algorithm>
 
#include <algorithm>
 
#include <iostream>
 
#include <iostream>
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     std::cout << "min element at: " << std::distance(v.begin(), result);
 
     std::cout << "min element at: " << std::distance(v.begin(), result);
 
}
 
}
−
| output=
+
|output=
 
min element at: 1
 
min element at: 1
 
}}
 
}}
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=212|std=C++98|before=the return value was not specified if {{c|1=first == last}}|after=returns {{c|last}} in this case}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/algorithm/dsc max_element}}
+
{{dsc inc|cpp/algorithm/dsc max_element}}
−
{{dsc inc | cpp/algorithm/dsc minmax_element}}
+
{{dsc inc|cpp/algorithm/dsc minmax_element}}
−
{{dsc inc | cpp/algorithm/dsc min}}
+
{{dsc inc|cpp/algorithm/dsc min}}
−
{{dsc inc | cpp/algorithm/ranges/dsc min_element}}
+
{{dsc inc|cpp/algorithm/ranges/dsc min_element}}
 
{{dsc end}}
 
{{dsc end}}
  
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
 
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Revision as of 01:23, 10 October 2022

 
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)

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)
min_element
(C++11)

Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
(1)
template< class ForwardIt >
ForwardIt min_element( ForwardIt first, ForwardIt last );
 (until C++17)
template< class ForwardIt >
constexpr ForwardIt min_element( ForwardIt first, ForwardIt last );
 (since C++17)
template< class ExecutionPolicy, class ForwardIt >

ForwardIt min_element( ExecutionPolicy&& policy,

                       ForwardIt first, ForwardIt last );
 (2) (since C++17)
(3)
template< class ForwardIt, class Compare >
ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );
 (until C++17)
template< class ForwardIt, class Compare >

constexpr ForwardIt min_element( ForwardIt first, ForwardIt last,

                                 Compare comp );
 (since C++17)
template< class ExecutionPolicy, class ForwardIt, class Compare >

ForwardIt min_element( ExecutionPolicy&& policy,

                       ForwardIt first, ForwardIt last, Compare comp );
 (4) (since C++17)

Finds the smallest element in the range [first, last).

1) Elements are compared using operator<.
3) Elements are compared using the given binary comparison function comp.
2,4) Same as (1,3), 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

Parameters

first, last - forward iterators defining the range to examine
policy - the execution policy to use. See execution policy for details.
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if a is less than b.

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

bool cmp(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 an object of type ForwardIt can be dereferenced and then implicitly converted to both of them.

Type requirements
-
ForwardIt must meet the requirements of LegacyForwardIterator.

Return value

Iterator to the smallest element in the range [first, last). If several elements in the range are equivalent to the smallest element, returns the iterator to the first such element. Returns last if the range is empty.

Complexity

Exactly max(N-1,0) comparisons, where N = std::distance(first, last).

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.

Possible implementation

First version 
template<class ForwardIt>
ForwardIt min_element(ForwardIt first, ForwardIt last)
{
    if (first == last)
        return last;
 
    ForwardIt smallest = first;
    ++first;
 
    for (; first != last; ++first)
        if (*first < *smallest)
            smallest = first;
 
    return smallest;
}
Second version 
template<class ForwardIt, class Compare>
ForwardIt min_element(ForwardIt first, ForwardIt last, Compare comp)
{
    if (first == last)
        return last;
 
    ForwardIt smallest = first;
    ++first;
 
    for (; first != last; ++first)
        if (comp(*first, *smallest))
            smallest = first;
 
    return smallest;
}

Example

Run this code
#include <algorithm>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v{3, 1, 4, 1, 5, 9};
 
    std::vector<int>::iterator result = std::min_element(v.begin(), v.end());
    std::cout << "min element at: " << std::distance(v.begin(), result);
}

Output: 

min element at: 1

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 212 C++98 the return value was not specified if first == last returns last in this case

See also

 returns the largest element in a range
(function template) [edit]
(C++11)
 returns the smallest and the largest elements in a range
(function template) [edit]
returns the smaller of the given values
(function template) [edit]
(C++20)
 returns the smallest element in a range
(niebloid)[edit]
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