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Difference between revisions of "cpp/algorithm/max"

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< cpp‎ | algorithm
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{{cpp/title|max}}
 
{{cpp/title|max}}
−
{{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++14}}|
−
template< class T >  
+
template< class T >
 
const T& max( const T& a, const T& b );
 
const T& max( const T& a, const T& b );
 
}}
 
}}
−
{{ddcl list item | num=2 |
+
{{dcla|num=2|notes={{mark constexpr since c++14}}|
 
template< class T, class Compare >
 
template< class T, class Compare >
 
const T& max( const T& a, const T& b, Compare comp );
 
const T& max( const T& a, const T& b, Compare comp );
 
}}
 
}}
−
{{ddcl list end}}
+
{{dcla|num=3|notes={{mark constexpr since c++14}}|since=c++11|
 +
template< class T >
 +
T max( std::initializer_list<T> ilist );
 +
}}
 +
{{dcla|num=4|notes={{mark constexpr since c++14}}|since=c++11|
 +
template< class T, class Compare >
 +
T max( std::initializer_list<T> ilist, Compare comp );
 +
}}
 +
{{dcl end}}
 +
 
 +
Returns the greater of the given values.
 +
 
 +
@1,2@ Returns the greater 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.
  
−
Returns the greater of two values. The first version uses {{cpp|operator<}} to compare the values, the second version uses the given comparison function {{tt|comp}}.
+
@3,4@ Returns the greatest 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.
 +
:@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===
 
===Parameters===
−
{{param list begin}}
+
{{par begin}}
−
{{param list item | a, b | the values to compare}}
+
{{par|a, b|the values to compare}}
−
{{param list cmp | cmp | t1=T | if {{tt|a}} is ''less'' than {{tt|b}}}}  
+
{{par|ilist|initializer list with the values to compare}}
−
{{param list end}}
+
{{par cmp|comp|t1=T|{{c|a}} is ''less'' than {{c|b}}}}  
 +
{{par end}}
  
 
===Return value===
 
===Return value===
−
The greater of {{tt|a}} and {{tt|b}}.
+
@1,2@ The greater of {{c|a}} and {{c|b}}. If they are equivalent, returns {{c|a}}.
 +
 
 +
@3,4@ The greatest value in {{c|ilist}}. If several values are equivalent to the greatest, returns the leftmost one.
  
 
===Complexity===
 
===Complexity===
−
{{complex constant}}
+
@1@ Exactly one comparison using {{c/core|operator<}}.
  
−
===Equivalent function===
+
@2@ Exactly one application of the comparison function {{c|comp}}.
−
{{eq fun cpp
+
 
−
| 1=
+
@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 impl
 +
|title1=max (1)|ver1=1|1=
 
template<class T>  
 
template<class T>  
 
const T& max(const T& a, const T& b)
 
const T& max(const T& a, const T& b)
Line 35: Line 63:
 
     return (a < b) ? b : a;
 
     return (a < b) ? b : a;
 
}
 
}
−
| 2=
+
|title2=max (2)|ver2=2|2=
 
template<class T, class Compare>  
 
template<class T, class Compare>  
 
const T& max(const T& a, const T& b, Compare comp)
 
const T& max(const T& a, const T& b, Compare comp)
 
{
 
{
 
     return (comp(a, b)) ? b : a;
 
     return (comp(a, b)) ? b : a;
 +
}
 +
|title3=max (3)|ver3=3|3=
 +
template<class T>
 +
T max(std::initializer_list<T> ilist)
 +
{
 +
    return *std::max_element(ilist.begin(), ilist.end());
 +
}
 +
|title4=max (4)|ver4=4|4=
 +
template<class T, class Compare>
 +
T max(std::initializer_list<T> ilist, Compare comp)
 +
{
 +
    return *std::max_element(ilist.begin(), ilist.end(), comp);
 
}
 
}
 
}}
 
}}
 +
 +
===Notes===
 +
{{cpp/algorithm/minmax danger note|max}}
  
 
===Example===
 
===Example===
−
{{example cpp
+
{{example
−
|
+
|code=
−
| code=
+
 
#include <algorithm>
 
#include <algorithm>
 +
#include <iomanip>
 
#include <iostream>
 
#include <iostream>
−
+
#include <string_view>
 +
 
 
int main()
 
int main()
 
{
 
{
−
     std::cout << "larger of 1 and 9999: " << std::max(1, 9999) << std::endl;
+
    auto longest = [](const std::string_view s1, const std::string_view s2)
−
    std::cout << "larger of 'a' and 'b': " << std::max('a', 'b') << std::endl;
+
                  {
−
    std::cout << "larger of 3.14 and 2.71: " << std::max(3.14, 2.71) << std::endl;
+
                      return s1.size() < s2.size();
−
+
                  };
−
    return 0;
+
   
 +
     std::cout << "Larger of 69 and 96 is " << std::max(69, 96) << "\n"
 +
                "Larger of 'q' and 'p' is '" << std::max('q', 'p') << "'\n"
 +
                "Largest of 010, 10, 0X10, and 0B10 is "
 +
              << std::max({010, 10, 0X10, 0B10}) << '\n'
 +
              << R"(Longest of "long", "short", and "int" is )"
 +
              << std::quoted(std::max({"long", "short", "int"}, longest)) << '\n';
 
}
 
}
−
| output=
+
|output=
−
larger of 1 and 9999: 9999
+
Larger of 69 and 96 is 96
−
larger of 'a' and 'b': b
+
Larger of 'q' and 'p' is 'q'
−
larger of 3.14 and 2.71: 3.14
+
Largest of 010, 10, 0X10, and 0B10 is 16
 +
Longest of "long", "short", and "int" is "short"
 
}}
 
}}
 +
 +
===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===
 
===See also===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/algorithm/dcl list min}}
+
{{dsc inc|cpp/algorithm/dsc min}}
−
{{dcl list template | cpp/algorithm/dcl list minmax}}
+
{{dsc inc|cpp/algorithm/dsc minmax}}
−
{{dcl list template | cpp/algorithm/dcl list max_element}}
+
{{dsc inc|cpp/algorithm/dsc max_element}}
−
{{dcl list end}}
+
{{dsc inc|cpp/algorithm/dsc clamp}}
 +
{{dsc inc|cpp/algorithm/ranges/dsc max}}
 +
{{dsc end}}
 +
 
 +
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 00:14, 9 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)

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

Returns the greater of the given values.

1,2) Returns the greater 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 greatest 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.

Contents

[edit] Parameters

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

[edit] Return value

1,2) The greater of a and b. If they are equivalent, returns a.
3,4) The greatest value in ilist. If several values are equivalent to the greatest, returns the leftmost one.

[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

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

[edit] Notes

Capturing the result of std::max 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::max(n + 2, n * 2); // r is dangling

[edit] Example

Run this code
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <string_view>
 
int main()
{
    auto longest = [](const std::string_view s1, const std::string_view s2)
                   {
                       return s1.size() < s2.size();
                   };
 
    std::cout << "Larger of 69 and 96 is " << std::max(69, 96) << "\n"
                 "Larger of 'q' and 'p' is '" << std::max('q', 'p') << "'\n"
                 "Largest of 010, 10, 0X10, and 0B10 is "
              << std::max({010, 10, 0X10, 0B10}) << '\n'
              << R"(Longest of "long", "short", and "int" is )"
              << std::quoted(std::max({"long", "short", "int"}, longest)) << '\n';
}

Output: 

Larger of 69 and 96 is 96
Larger of 'q' and 'p' is 'q'
Largest of 010, 10, 0X10, and 0B10 is 16
Longest of "long", "short", and "int" is "short"

[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

 returns the smaller of the given values
(function template) [edit]
(C++11)
 returns the smaller and larger of two elements
(function template) [edit]
returns the largest element in a range
(function template) [edit]
(C++17)
 clamps a value between a pair of boundary values
(function template) [edit]
(C++20)
 returns the greater of the given values
(niebloid)[edit]
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