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Difference between revisions of "cpp/algorithm/max"

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< cpp‎ | algorithm
(lwg 2350 (constexpr))
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{{par cmp | comp | t1=T | if {{tt|a}} is ''less'' than {{tt|b}}}}  
 
{{par cmp | comp | t1=T | if {{tt|a}} is ''less'' than {{tt|b}}}}  
 
{{par hreq}}
 
{{par hreq}}
−
{{par req concept | T | LessThanComparable | notes=for the overloads (1) and (3)}}
+
{{par req concept | T | LessThanComparable | overloads=1,3}}
−
{{par req concept | T | CopyConstructible | notes=for the overloads (3) and (4)}}
+
{{par req concept | T | CopyConstructible | overloads=3,4}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
1-2) The greater of {{tt|a}} and {{tt|b}}. If they are equivalent, returns {{tt|a}}.
+
@1-2@ The greater of {{tt|a}} and {{tt|b}}. If they are equivalent, returns {{tt|a}}.
  
−
3-4) The greatest value in {{tt|ilist}}. If several values are equivalent to the greatest, returns the leftmost one.
+
@3-4@ The greatest value in {{tt|ilist}}. If several values are equivalent to the greatest, returns the leftmost one.
  
 
===Complexity===
 
===Complexity===
−
1-2) Constant
+
@1-2@ Exactly one comparison
  
−
3-4) Linear in {{tt|ilist.size()}}
+
@3-4@ Exactly {{tt|ilist.size() - 1}} comparisons
  
 
===Possible implementation===
 
===Possible implementation===

Revision as of 10:00, 23 May 2015

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

Returns the greater of the given values.

1-2) Returns the greater of a and b.
3-4) Returns the greatest 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
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if 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

Template:par req concept Template:par req concept

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.

Complexity

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

Possible implementation

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

Example

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

Output: 

larger of 1 and 9999: 9999
larger of 'a', and 'b': b
longest of "foo", "bar", and "hello": hello

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]
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