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# std::max

From cppreference.com
< cpp‎ | algorithm

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`.

### [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 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).

### [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

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

### [edit] See also

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

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