std::max

 

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Technical Specifications

 

Algorithm library

Execution policies (C++17)
is_execution_policy	execution::seqexecution::parexecution::par_unseq	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policy
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_3way (C++20)
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17)	uninitialized_copy_n (C++11) uninitialized_move_n (C++17)	uninitialized_fill	uninitialized_fill_n
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is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
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is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
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lower_bound	upper_bound	binary_search	equal_range
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merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
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is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
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max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17) compare_3way (C++20)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
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iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

 

Defined in header <algorithm>
	(1)
template<class T > const T& max(const T& a, const T& b );			(until C++14)
template<class T > constexprconst 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 > constexprconst 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.

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); The signature does not need to have const&, but the function object must not modify the objects passed to it. 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 if one of the parameters is rvalue produces a dangling reference if that parameter is returned:

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

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"}, [](conststd::string& s1, conststd::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

min	returns the smaller of the given values (function template)
minmax (C++11)	returns the smaller and larger of two elements (function template)
max_element	returns the largest element in a range (function template)