NAME

std::min - std::min

Synopsis

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

Returns the smaller of the given values.

1-2) Returns the smaller of a and b.
3-4) Returns the smallest 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);
cmp -
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 smaller of a and b. If the values are equivalent, returns a.
3-4) The smallest value in ilist. If several values are equivalent to the smallest,
returns the leftmost such value.

Complexity

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

Possible implementation

First version

template<class T>
const T& min(const T& a, const T& b)
{
return (b < a) ? b : a;
}

Second version

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

Notes

Capturing the result of std::min 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::min(n-1, n+1);
// r is dangling

Example

// Run this code

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

int main()
{
std::cout << "smaller of 1 and 9999 is " << std::min(1, 9999) << '\n'
<< "smaller of 'a', and 'b' is '" << std::min('a', 'b') << "'\n"
<< "shortest of \"foo\", \"bar\", and \"hello\" is \""
<< std::min({ "foo", "bar", "hello" },
[](const std::string_view s1, const std::string_view s2) {
return s1.size() < s2.size();
}) << "\"\n";
}

Output:

smaller of 1 and 9999 is 1
smaller of 'a', and 'b' is 'a'
shortest of "foo", "bar", and "hello" is "foo"