Difference between revisions of "cpp/algorithm/min"

Latest revision as of 01:13, 9 April 2024

Defined in header `<algorithm>`
template< class T > const T& min( const T& a, const T& b );	(1)	(constexpr since C++14)
template< class T, class Compare > const T& min( const T& a, const T& b, Compare comp );	(2)	(constexpr since C++14)
template< class T > T min( std::initializer_list<T> ilist );	(3)	(since C++11) (constexpr since C++14)
template< class T, class Compare > T min( std::initializer_list<T> ilist, Compare comp );	(4)	(since C++11) (constexpr since C++14)

Returns the smaller of the given values.

1,2) Returns the smaller of a and b.

1) Uses operator< to compare the values.

If T is not LessThanComparable, the behavior is undefined.

2) Use the comparison function comp to compare the values.

3,4) Returns the smallest of the values in initializer list ilist.

If ilist.size() is zero, or T is not CopyConstructible, the behavior is undefined.

3) Uses operator< to compare the values.

If T is not LessThanComparable, the behavior is undefined.

4) Use the comparison function comp to compare the values.

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.

[edit] 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.

[edit] Complexity

1) Exactly one comparison using operator<.

2) Exactly one application of the comparison function comp.

3,4) Given

N

as ilist.size():

3) Exactly

N-1

comparisons using operator<.

4) Exactly

N-1

applications of the comparison function comp.

[edit] Possible implementation

min (1)
template<class T> const T& min(const T& a, const T& b) { return (b < a) ? b : a; }
min (2)
template<class T, class Compare> const T& min(const T& a, const T& b, Compare comp) { return (comp(b, a)) ? b : a; }
min (3)
template<class T> T min(std::initializer_list<T> ilist) { return *std::min_element(ilist.begin(), ilist.end()); }
min (4)
template<class T, class Compare> T min(std::initializer_list<T> ilist, Compare comp) { return *std::min_element(ilist.begin(), ilist.end(), comp); }

[edit] Notes

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

[edit] Example

Run this code

#include <algorithm>
#include <iostream>
#include <string_view>
 
int main()
{
    std::cout << "smaller of 10 and 010 is " << std::min(10, 010) << '\n'
              << "smaller of 'd' and 'b' is '" << std::min('d', '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 10 and 010 is 8
smaller of 'd' and 'b' is 'b'
shortest of "foo", "bar", and "hello" is "foo"

[edit] 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 281	C++98	`T` was required to be CopyConstructible for overloads (1,2)	not required

[edit] See also

max	returns the greater of the given values (function template) [edit]
minmax (C++11)	returns the smaller and larger of two elements (function template) [edit]
min_element	returns the smallest element in a range (function template) [edit]
clamp (C++17)	clamps a value between a pair of boundary values (function template) [edit]
ranges::min (C++20)	returns the smaller of the given values (niebloid)[edit]

@@ Line 2: / Line 2: @@
 {{cpp/algorithm/navbar}}
 {{dcl begin}}
-{{dcl header | algorithm}}
+{{dcl header|algorithm}}
-{{dcl rev begin|num=1}}
+{{dcla|num=1|notes={{mark constexpr since c++14}}|
-{{dcl | until=c++14 |
+template< class T >
-template< class T >
 const T& min( const T& a, const T& b );
 }}
-{{dcl | since=c++14 |
+{{dcla|num=2|notes={{mark constexpr since c++14}}|
-template< class T >
-constexpr const T& min( const T& a, const T& b );
-}}
-{{dcl rev end}}
-{{dcl rev begin|num=2}}
-{{dcl | until=c++14 |
 template< class T, class Compare >
 const T& min( const T& a, const T& b, Compare comp );
 }}
-{{dcl | since=c++14 |
+{{dcla|num=3|notes={{mark constexpr since c++14}}|since=c++11|
-template< class T, class Compare >
-constexpr const T& min( const T& a, const T& b, Compare comp );
-}}
-{{dcl rev end}}
-{{dcl rev begin|num=3}}
-{{dcl | since=c++11| until=c++14 |
 template< class T >
 T min( std::initializer_list<T> ilist );
 }}
-{{dcl | since=c++14 |
+{{dcla|num=4|notes={{mark constexpr since c++14}}|since=c++11|
-template< class T >
-constexpr T min( std::initializer_list<T> ilist );
-}}
-{{dcl rev end}}
-{{dcl rev begin|num=4}}
-{{dcl | since=c++11 | until=c++14 |
 template< class T, class Compare >
 T min( std::initializer_list<T> ilist, Compare comp );
 }}
-{{dcl | since=c++14 |
-template< class T, class Compare >
-constexpr T min( std::initializer_list<T> ilist, Compare comp );
-}}
-{{dcl rev end}}
 {{dcl end}}
 Returns the smaller of the given values.
-@1-2@ Returns the smaller of {{tt|a}} and {{tt|b}}.
+@1,2@ Returns the smaller of {{c|a}} and {{c|b}}.
+:@1@ Uses {{c/core|operator<}} to compare the values.
+:@@ If {{tt|T}} is not {{named req|LessThanComparable}}, the behavior is undefined.
+:@2@ Use the comparison function {{c|comp}} to compare the values.
-@3-4@ Returns the smallest of the values in initializer list {{tt|ilist}}.
+@3,4@ Returns the smallest of the values in initializer list {{c|ilist}}.
+@@ If {{c|ilist.size()}} is zero, or {{tt|T}} is not {{named req|CopyConstructible}}, the behavior is undefined.
-The {{v|1,3}} versions use {{c|operator<}} to compare the values, the {{v|2,4}} versions use the given comparison function {{tt|comp}}.
+:@3@ Uses {{c/core|operator<}} to compare the values.
+:@@ If {{tt|T}} is not {{named req|LessThanComparable}}, the behavior is undefined.
+:@4@ Use the comparison function {{c|comp}} to compare the values.
 ===Parameters===
 {{par begin}}
-{{par | a, b | the values to compare}}
+{{par|a, b|the values to compare}}
-{{par | ilist | initializer list with the values to compare}}
+{{par|ilist|initializer list with the values to compare}}
-{{par cmp | cmp | t1=T | if {{tt|a}} is ''less'' than {{tt|b}}}}
+{{par cmp|cmp|t1=T|{{c|a}} is ''less'' than {{c|b}}}}
-{{par hreq}}
-{{par req named | T | LessThanComparable | overloads=1,3}}
-{{par req named | T | CopyConstructible | overloads=3,4}}
 {{par end}}
 ===Return value===
-@1-2@ The smaller of {{tt|a}} and {{tt|b}}. If the values are equivalent, returns {{tt|a}}.
+@1,2@ The smaller of {{c|a}} and {{c|b}}. If the values are equivalent, returns {{c|a}}.
-@3-4@ The smallest value in {{tt|ilist}}. If several values are equivalent to the smallest, returns the leftmost such value.
+@3,4@ The smallest value in {{c|ilist}}. If several values are equivalent to the smallest, returns the leftmost such value.
 ===Complexity===
-@1-2@ Exactly one comparison
+@1@ Exactly one comparison using {{c/core|operator<}}.
-@3-4@ Exactly {{tt|ilist.size() - 1}} comparisons
+@2@ Exactly one application of the comparison function {{c|comp}}.
+@3,4@ Given {{mathjax-or|\(\scriptsize N\)|N}} as {{c|ilist.size()}}:
+:@3@ Exactly {{mathjax-or|\(\scriptsize N-1\)|N-1}} comparisons using {{c/core|operator<}}.
+:@4@ Exactly {{mathjax-or|\(\scriptsize N-1\)|N-1}} applications of the comparison function {{c|comp}}.
 ===Possible implementation===
-{{eq fun
+{{eq impl
- | 1=
+|title1=min (1)|ver1=1|1=
 template<class T>
 const T& min(const T& a, const T& b)
 {
      return (b < a) ? b : a;
 }
- | 2=
+|title2=min (2)|ver2=2|2=
 template<class T, class Compare>
 const T& min(const T& a, const T& b, Compare comp)
 {
      return (comp(b, a)) ? b : a;
 }
- | 3=
+|title3=min (3)|ver3=3|3=
 template<class T>
-T min( std::initializer_list<T> ilist)
+T min(std::initializer_list<T> ilist)
 {
      return *std::min_element(ilist.begin(), ilist.end());
 }
- | 4=
+|title4=min (4)|ver4=4|4=
 template<class T, class Compare>
 T min(std::initializer_list<T> ilist, Compare comp)
@@ Line 101: / Line 83: @@
 }}
-===Warning===
+===Notes===
-{{cpp/algorithm/minmax_danger_note|min}}
+{{cpp/algorithm/minmax danger note|min}}
 ===Example===
 {{example
- |
+|code=
- | code=
 #include <algorithm>
 #include <iostream>
-#include <string>
+#include <string_view>
 int main()
 {
-     std::cout << "smaller of 1 and 9999: " << std::min(1, 9999) << '\n'
+     std::cout << "smaller of 10 and 010 is " << std::min(10, 010) << '\n'
-               << "smaller of 'a', and 'b': " << std::min('a', 'b') << '\n'
+               << "smaller of 'd' and 'b' is '" << std::min('d', 'b') << "'\n"
-               << "shortest of \"foo\", \"bar\", and \"hello\": " <<
+               << "shortest of \"foo\", \"bar\", and \"hello\" is \""
-                  std::min( { "foo", "bar", "hello" },
+              << std::min({"foo", "bar", "hello"},
-                            [](const std::string& s1, const std::string& s2) {
+                          [](const std::string_view s1, const std::string_view s2)
-                                 return s1.size() < s2.size();
+                          {
-                             }) << '\n';
+                              return s1.size() < s2.size();
+                          }) << "\"\n";
 }
- | output=
+|output=
-smaller of 1 and 9999: 1
+smaller of 10 and 010 is 8
-smaller of 'a', and 'b': a
+smaller of 'd' and 'b' is 'b'
-shortest of "foo", "bar", and "hello": foo
+shortest of "foo", "bar", and "hello" is "foo"
 }}
+===Defect reports===
+{{dr list begin}}
+{{dr list item|wg=lwg|dr=281|std=C++98|before={{tt|T}} was required to be {{named req|CopyConstructible}} for overloads {{v|1,2}}|after=not required}}
+{{dr list end}}
 ===See also===
 {{dsc begin}}
-{{dsc inc | cpp/algorithm/dsc max}}
+{{dsc inc|cpp/algorithm/dsc max}}
-{{dsc inc | cpp/algorithm/dsc minmax}}
+{{dsc inc|cpp/algorithm/dsc minmax}}
-{{dsc inc | cpp/algorithm/dsc min_element}}
+{{dsc inc|cpp/algorithm/dsc min_element}}
+{{dsc inc|cpp/algorithm/dsc clamp}}
+{{dsc inc|cpp/algorithm/ranges/dsc min}}
 {{dsc end}}
-[[de:cpp/algorithm/min]]
+{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
-[[es:cpp/algorithm/min]]
-[[fr:cpp/algorithm/min]]
-[[it:cpp/algorithm/min]]
-[[ja:cpp/algorithm/min]]
-[[pt:cpp/algorithm/min]]
-[[ru:cpp/algorithm/min]]
-[[zh:cpp/algorithm/min]]

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Difference between revisions of "cpp/algorithm/min"

Latest revision as of 01:13, 9 April 2024

Contents

[edit] Parameters