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std::max

From cppreference.com
< cpp‎ | algorithm
 
 
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)
Permutations
Numeric operations
C library
 
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

[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. ​

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).

[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

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

[edit] 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);
}

[edit] Notes

Capturing the result of std::max by reference if one of the parameters is rvalue produces a dangling reference if that parameter is returned:

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

[edit] Example

#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

[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]