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Difference between revisions of "cpp/algorithm/min"

From cppreference.com
< cpp‎ | algorithm
m (fmt; + legacy strlen does not create temporaries (sso-optimized strings))
(→‎Example: target C++17)
Line 110: Line 110:
 
#include <algorithm>
 
#include <algorithm>
 
#include <iostream>
 
#include <iostream>
−
#include <cstring>
+
#include <string_view>
  
 
int main()
 
int main()
Line 118: Line 118:
 
               << "shortest of \"foo\", \"bar\", and \"hello\" is \""
 
               << "shortest of \"foo\", \"bar\", and \"hello\" is \""
 
               << std::min({ "foo", "bar", "hello" },
 
               << std::min({ "foo", "bar", "hello" },
−
                           [](const char* s1, const char* s2) {
+
                           [](const std::string_view s1, const std::string_view s2) {
−
                               return std::strlen(s1) < std::strlen(s2);
+
                               return s1.size() < s2.size();
 
                           }) << "\"\n";
 
                           }) << "\"\n";
 
}
 
}

Revision as of 17:30, 29 July 2020

 
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
min
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
(1)
template< class T >
const T& min( const T& a, const T& b );
 (until C++14)
template< class T >
constexpr const T& min( const T& a, const T& b );
 (since C++14)
(2)
template< class T, class Compare >
const T& min( const T& a, const T& b, Compare comp );
 (until C++14)
template< class T, class Compare >
constexpr const T& min( const T& a, const T& b, Compare comp );
 (since C++14)
(3)
template< class T >
T min( std::initializer_list<T> ilist );
 (since C++11)
(until C++14)
template< class T >
constexpr T min( std::initializer_list<T> ilist );
 (since C++14)
(4)
template< class T, class Compare >
T min( std::initializer_list<T> ilist, Compare comp );
 (since C++11)
(until C++14)
template< class T, class Compare >
constexpr T min( std::initializer_list<T> ilist, Compare comp );
 (since C++14)

Returns the smaller of the given values.

1-2) Returns the smaller of a and b.
3-4) Returns the smallest of the values in initializer list ilist.

The (1,3) versions use operator< to compare the values, the (2,4) versions use the given comparison function comp.

Contents

Parameters

a, b - the values to compare
ilist - initializer list with the values to compare
cmp - 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 T can be implicitly converted to both of them.

Type requirements
-
T must meet the requirements of LessThanComparable in order to use overloads (1,3).
-
T must meet the requirements of CopyConstructible in order to use overloads (3,4).

Return value

1-2) The smaller of a and b. If the values are equivalent, returns a.
3-4) The smallest value in ilist. If several values are equivalent to the smallest, returns the leftmost such value.

Complexity

1-2) Exactly one comparison
3-4) Exactly ilist.size() - 1 comparisons

Possible implementation

First version 
template<class T> 
const T& min(const T& a, const T& b)
{
    return (b < a) ? b : a;
}
Second version 
template<class T, class Compare> 
const T& min(const T& a, const T& b, Compare comp)
{
    return (comp(b, a)) ? b : a;
}
Third version 
template<class T>
T min( std::initializer_list<T> ilist)
{
    return *std::min_element(ilist.begin(), ilist.end());
}
Fourth version 
template<class T, class Compare>
T min(std::initializer_list<T> ilist, Compare comp)
{
    return *std::min_element(ilist.begin(), ilist.end(), comp);
}

Warning

Capturing the result of std::min by reference produces a dangling reference if one of the parameters is a temporary and that parameter is returned: 

int n = -1;
const int& r = std::min(n + 2, n * 2); // r is dangling

Example

Run this code
#include <algorithm>
#include <iostream>
#include <string_view>
 
int main()
{
    std::cout << "smaller of 1 and 9999 is " << std::min(1, 9999) << '\n'
              << "smaller of 'a', and 'b' is '" << std::min('a', 'b') << "'\n"
              << "shortest of \"foo\", \"bar\", and \"hello\" is \""
              << std::min({ "foo", "bar", "hello" },
                          [](const std::string_view s1, const std::string_view s2) {
                              return s1.size() < s2.size();
                          }) << "\"\n";
}

Output: 

smaller of 1 and 9999 is 1
smaller of 'a', and 'b' is 'a'
shortest of "foo", "bar", and "hello" is "foo"

See also

 returns the greater of the given values
(function template) [edit]
(C++11)
 returns the smaller and larger of two elements
(function template) [edit]
returns the smallest element in a range
(function template) [edit]
(C++17)
 clamps a value between a pair of boundary values
(function template) [edit]
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