NAME¶

std::max - std::max

Synopsis¶

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

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.

Parameters¶

a, b - the values to compare
ilist - initializer list with the values to compare
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);
comp -
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 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);
}

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-1, n+1);
// r is dangling

Example¶

// Run this code

#include <algorithm>
#include <iostream>
#include <string_view>

int main()
{
std::cout << "larger of 1 and 9999 is " << std::max(1, 9999) << '\n'
<< "larger of 'a', and 'b' is '" << std::max('a', 'b') << "'\n"
<< "largest of 1, 10, 50, and 200 is " << std::max({1, 10, 50, 200}) << '\n'
<< "longest of \"foo\", \"bar\", and \"hello\" is \""
<< std::max({ "foo", "bar", "hello" },
[](const std::string_view s1, const std::string_view s2) {
return s1.size() < s2.size();
}) << "\"\n";
}

Output:¶

larger of 1 and 9999 is 9999
larger of 'a', and 'b' is 'b'
largest of 1, 10, 50, and 200 is 200
longest of "foo", "bar", and "hello" is "hello"

See also¶

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